Showing papers on "Cell growth published in 2004"
TL;DR: In this article, the authors identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts.
Abstract: MDM2 binds the p53 tumor suppressor protein with high affinity and negatively modulates its transcriptional activity and stability. Overexpression of MDM2, found in many human tumors, effectively impairs p53 function. Inhibition of MDM2-p53 interaction can stabilize p53 and may offer a novel strategy for cancer therapy. Here, we identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes. These compounds bind MDM2 in the p53-binding pocket and activate the p53 pathway in cancer cells, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts in nude mice.
4,397 citations
TL;DR: Mucins — large extracellular proteins that are heavily glycosylated with complex oligosaccharides — establish a selective molecular barrier at the epithelial surface and engage in morphogenetic signal transduction.
Abstract: Mucins — large extracellular proteins that are heavily glycosylated with complex oligosaccharides — establish a selective molecular barrier at the epithelial surface and engage in morphogenetic signal transduction. Alterations in mucin expression or glycosylation accompany the development of cancer and influence cellular growth, differentiation, transformation, adhesion, invasion and immune surveillance. Mucins are used as diagnostic markers in cancer, and are under investigation as therapeutic targets for cancer.
1,657 citations
TL;DR: This review examines the evidence of cellular oxidants' involvement in the carcinogenesis process, and focuses on the mechanisms for production, cellular damage produced, and the role of signaling cascades by reactive oxygen species.
Abstract: ▪ Abstract Chemical carcinogenesis follows a multistep process involving both mutation and increased cell proliferation. Oxidative stress can occur through overproduction of reactive oxygen and nitrogen species through either endogenous or exogenous insults. Important to carcinogenesis, the unregulated or prolonged production of cellular oxidants has been linked to mutation (induced by oxidant-induced DNA damage), as well as modification of gene expression. In particular, signal transduction pathways, including AP-1 and NFκB, are known to be activated by reactive oxygen species, and they lead to the transcription of genes involved in cell growth regulatory pathways. This review examines the evidence of cellular oxidants' involvement in the carcinogenesis process, and focuses on the mechanisms for production, cellular damage produced, and the role of signaling cascades by reactive oxygen species.
1,487 citations
TL;DR: It is shown that mTOR inhibition by hypoxia requires the TSC1/TSC2 tumor suppressor complex and the Hypoxia-inducible gene REDD1/RTP801 to be inhibited, and that down-regulation of mTOR activity by hyp oxia requires de novo mRNA synthesis and correlates with increased expression of the hypoxIA-Inducible REDD 1 gene.
Abstract: Mammalian target of rapamycin (mTOR) is a central regulator of protein synthesis whose activity is modulated by a variety of signals. Energy depletion and hypoxia result in mTOR inhibition. While energy depletion inhibits mTOR through a process involving the activation of AMP-activated protein kinase (AMPK) by LKB1 and subsequent phosphorylation of TSC2, the mechanism of mTOR inhibition by hypoxia is not known. Here we show that mTOR inhibition by hypoxia requires the TSC1/TSC2 tumor suppressor complex and the hypoxia-inducible gene REDD1/RTP801. Disruption of the TSC1/TSC2 complex through loss of TSC1 or TSC2 blocks the effects of hypoxia on mTOR, as measured by changes in the mTOR targets S6K and 4E-BP1, and results in abnormal accumulation of Hypoxia-inducible factor (HIF). In contrast to energy depletion, mTOR inhibition by hypoxia does not require AMPK or LKB1. Down-regulation of mTOR activity by hypoxia requires de novo mRNA synthesis and correlates with increased expression of the hypoxia-inducible REDD1 gene. Disruption of REDD1 abrogates the hypoxia-induced inhibition of mTOR, and REDD1 overexpression is sufficient to down-regulate S6K phosphorylation in a TSC1/TSC2-dependent manner. Inhibition of mTOR function by hypoxia is likely to be important for tumor suppression as TSC2-deficient cells maintain abnormally high levels of cell proliferation under hypoxia.
1,299 citations
TL;DR: TOR is emerging as a novel antitumor target, since the TOR inhibitor rapamycin appears to be effective against tumors resulting from aberrantly high PI3K signaling.
Abstract: Cell growth (an increase in cell mass and size through macromolecular biosynthesis) and cell cycle progression are generally tightly coupled, allowing cells to proliferate continuously while maintaining their size. The target of rapamycin (TOR) is an evolutionarily conserved kinase that integrates signals from nutrients (amino acids and energy) and growth factors (in higher eukaryotes) to regulate cell growth and cell cycle progression coordinately. In mammals, TOR is best known to regulate translation through the ribosomal protein S6 kinases (S6Ks) and the eukaryotic translation initiation factor 4E-binding proteins. Consistent with the contribution of translation to growth, TOR regulates cell, organ, and organismal size. The identification of the tumor suppressor proteins tuberous sclerosis1 and 2 (TSC1 and 2) and Ras-homolog enriched in brain (Rheb) has biochemically linked the TOR and phosphatidylinositol 3-kinase (PI3K) pathways, providing a mechanism for the crosstalk that occurs between these pathways. TOR is emerging as a novel antitumor target, since the TOR inhibitor rapamycin appears to be effective against tumors resulting from aberrantly high PI3K signaling. Not only may inhibition of TOR be effective in cancer treatment, but rapamycin is an FDA-approved immunosuppressive and cardiology drug. We review here what is known (and not known) about the function of TOR in cellular and animal physiology.
1,206 citations
TL;DR: Junctional structures maintain the integrity of the endothelium and might transfer intracellular signals that regulate contact-induced inhibition of cell growth, apoptosis, gene expression and new vessel formation.
Abstract: Junctional structures maintain the integrity of the endothelium Recent studies have shown that, as well as promoting cell–cell adhesion, junctions might transfer intracellular signals that regulate contact-induced inhibition of cell growth, apoptosis, gene expression and new vessel formation Moreover, modifications of the molecular organization and intracellular signalling of junctional proteins might have complex effects on vascular homeostasis
1,157 citations
TL;DR: An increasingly complex and coherent view of G1 signalling networks, which coordinate cell growth, proliferation, stress management and survival, is helping to define the roots of malignancies and shows promise for the development of better cancer therapies.
Abstract: Before replicating DNA during their reproductive cycle, our cells enter a phase called G1 during which they interpret a flood of signals that influence cell division and cell fate. Mistakes in this process lead to cancer. An increasingly complex and coherent view of G1 signalling networks, which coordinate cell growth, proliferation, stress management and survival, is helping to define the roots of malignancies and shows promise for the development of better cancer therapies.
1,148 citations
TL;DR: It is reported that mTOR inhibition induced apoptosis of epithelial cells and the complete reversal of a neoplastic phenotype in the prostate of mice expressing human AKT1 in the ventral prostate, and that clinical resistance to mTOR inhibitors may emerge through BCL2 expression and/or upregulation of HIF-1α activity.
Abstract: Loss of PTEN function leads to activation of phosphoinositide 3-kinase (PI3K) signaling and Akt. Clinical trials are now testing whether mammalian target of rapamycin (mTOR) inhibition is useful in treating PTEN-null cancers. Here, we report that mTOR inhibition induced apoptosis of epithelial cells and the complete reversal of a neoplastic phenotype in the prostate of mice expressing human AKT1 in the ventral prostate. Induction of cell death required the mitochondrial pathway, as prostate-specific coexpression of BCL2 blocked apoptosis. Thus, there is an mTOR-dependent survival signal required downstream of Akt. Bcl2 expression, however, only partially restored intraluminal cell growth in the setting of mTOR inhibition. Expression profiling showed that Hif-1 alpha targets, including genes encoding most glycolytic enzymes, constituted the dominant transcriptional response to AKT activation and mTOR inhibition. These data suggest that the expansion of AKT-driven prostate epithelial cells requires mTOR-dependent survival signaling and activation of HIF-1 alpha, and that clinical resistance to mTOR inhibitors may emerge through BCL2 expression and/or upregulation of HIF-1 alpha activity.
929 citations
TL;DR: Preliminary data indicate that HIF plays a critical role in pVHL-defective tumor formation, raising the possibility that drugs directed against HIF or its downstream targets (such as vascular endothelial growth factor) might one day play a role in the treatment of hemangioblastoma and renal cell carcinoma.
Abstract: Germline inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene causes the von Hippel-Lindau hereditary cancer syndrome, and somatic mutations of this gene have been linked to the development of sporadic hemangioblastomas and clear-cell renal carcinomas. The VHL tumor suppressor protein (pVHL), through its oxygen-dependent polyubiquitylation of hypoxia-inducible factor (HIF), plays a central role in the mammalian oxygen-sensing pathway. This interaction between pVHL and HIF is governed by post-translational prolyl hydroxylation of HIF in the presence of oxygen by a conserved family of Egl-nine (EGLN) enzymes. In the absence of pVHL, HIF becomes stabilized and is free to induce the expression of its target genes, many of which are important in regulating angiogenesis, cell growth, or cell survival. Moreover, preliminary data indicate that HIF plays a critical role in pVHL-defective tumor formation, raising the possibility that drugs directed against HIF or its downstream targets (such as vascular endothelial growth factor) might one day play a role in the treatment of hemangioblastoma and renal cell carcinoma. On the other hand, clear genotype-phenotype correlations are emerging in VHL disease and can be rationalized if pVHL has functions separate from its control of HIF.
908 citations
TL;DR: It is demonstrated that, as for the regulation of cell growth and cell size, the S6K1 and 4E-BP1/eIF4E pathways each represent critical mediators of mTOR-dependent cell cycle control.
Abstract: The mammalian target of rapamycin (mTOR) integrates nutrient and mitogen signals to regulate cell growth (increased cell mass and cell size) and cell division. The immunosuppressive drug rapamycin inhibits cell cycle progression via inhibition of mTOR; however, the signaling pathways by which mTOR regulates cell cycle progression have remained poorly defined. Here we demonstrate that restoration of mTOR signaling (by using a rapamycin-resistant mutant of mTOR) rescues rapamycin-inhibited G1-phase progression, and restoration of signaling along the mTOR-dependent S6K1 or 4E-BP1/eukaryotic translation initiation factor 4E (eIF4E) pathways provides partial rescue. Furthermore, interfering RNA-mediated reduction of S6K1 expression or overexpression of mTOR-insensitive 4E-BP1 isoforms that block eIF4E activity inhibit G1-phase progression individually and additively. Thus, the activities of both the S6K1 and 4E-BP1/eIF4E pathways are required for and independently mediate mTOR-dependent G1-phase progression. In addition, overexpression of constitutively active mutants of S6K1 or wild-type eIF4E accelerates serum-stimulated G1-phase progression, and stable expression of wild-type S6K1 confers a proliferative advantage in low-serum-containing media, suggesting that the activity of each of these pathways is limiting for cell proliferation. These data demonstrate that, as for the regulation of cell growth and cell size, the S6K1 and 4E-BP1/eIF4E pathways each represent critical mediators of mTOR-dependent cell cycle control.
829 citations
TL;DR: It is shown that Fbw7, a component of the SCFFbw 7 ubiquitin ligase and a tumor suppressor, promotes proteasome-dependent c-Myc turnover in vivo and c- myc ubiquitination in vitro.
Abstract: Myc proteins regulate cell growth and division and are implicated in a wide range of human cancers. We show here that Fbw7, a component of the SCFFbw7 ubiquitin ligase and a tumor suppressor, promotes proteasome-dependent c-Myc turnover in vivo and c-Myc ubiquitination in vitro. Phosphorylation of c-Myc on threonine-58 (T58) by glycogen synthase kinase 3 regulates the binding of Fbw7 to c-Myc as well as Fbw7-mediated c-Myc degradation and ubiquitination. T58 is the most frequent site of c-myc mutations in lymphoma cells, and our findings suggest that c-Myc activation is one of the key oncogenic consequences of Fbw7 loss in cancer. Because Fbw7 mediates the degradation of cyclin E, Notch, and c-Jun, as well as c-Myc, the loss of Fbw7 is likely to elicit profound effects on cell proliferation during tumorigenesis.
TL;DR: The results indicate that D-type cyclin-dependent kinases are not essential for cell cycle entry and suggest the existence of alternative mechanisms to initiate cell proliferation upon mitogenic stimulation.
TL;DR: It is shown that mice deficient for S 6K1 or S6K2 are born at the expected Mendelian ratio, and analysis of S6 phosphorylation in the cytoplasm and nucleoli of cells derived from the distinct S7K genotypes suggests that both kinases are required for full S6osphorylation but that S6k2 may be more prevalent in contributing to this response.
Abstract: Recent studies showed that the 40S ribosomal protein S6 kinase (S6K) p70S6K/p85S6K, termed S6K1 (51), is a major effector of cell growth. This conclusion stems from gene deletion studies with Drosophila (39) and with mice (51) as well as recent studies with cell cultures (11). The loss of the Drosophila S6K (dS6K) gene is semilethal, with the few surviving adults having a severely reduced body size. The larvae of such flies exhibit a long developmental delay, consistent with a twofold increase in cell cycle doubling times. The few surviving adults are quite lethargic, living no longer than 2 weeks, and females are sterile. Surprisingly, the reduction in mass is strictly due to a decrease in cell size rather than to a decrease in cell number (39).
In mice, removal of this kinase is not lethal, but the mice are approximately 20% smaller at birth (51). Such mice exhibit normal fasting glucose levels but are mildly glucose intolerant due to markedly reduced levels of circulating insulin (42). Reduced insulin levels are caused by a reduction in pancreatic endocrine mass and an impairment of insulin secretion, which can be traced to a selective reduction in β-cell size. Unexpectedly, the effects on body mass and hypoinsulinemia do not appear to be attributable to a reduction in S6 phosphorylation, as this response proved to be largely intact in S6K1-deficient animals (51). However, S6 phosphorylation in such animals was still sensitive to the bacterial macrolide rapamycin (51), which inhibits the mammalian target of rapamycin (mTOR) (1, 7, 16, 48), the upstream S6K1 kinase (4, 8, 18), suggesting the existence of a second S6K. Subsequent searches of expressed sequence tag databases and biochemical studies led to the identification of S6K2, which exhibited overall homology of over 80% with S6K1 in the highly conserved kinase and linker domains (17, 47, 51). In all tissues examined from S6K1-deficient mice, S6K2 transcripts were upregulated (51). From this observation, it was reasoned that S6K1 and S6K2 functions were redundant and that a deletion of the S6K1 gene led to a compensatory increase in the expression of S6K2.
In parallel studies, it was demonstrated that rapamycin suppressed the serum-induced translational upregulation of a family of mRNAs which contain a polypyrimidine tract at their 5′ end (5′-terminal oligopyrimidine [5′TOP] mRNAs) (20, 55). These mRNAs largely code for components of the translational apparatus, most notably, ribosomal proteins (37). Earlier studies had shown that the translation of such transcripts is under selective translational control (22) and requires an intact 5′TOP tract (19, 49). In addition, a dominant interfering allele of S6K1 inhibited the mitogen-induced translational upregulation of 5′TOP mRNAs to the same extent as rapamycin, whereas an activated allele of S6K1, which exhibits a substantial degree of rapamycin resistance, largely protected these transcripts from the inhibitory effects of rapamycin (19, 49).
Seemingly consistent with these arguments, in embryonic stem (ES) cells from which S6K1 had been homologously deleted by selection with high doses of G418, serum no longer had an effect on the upregulation of 5′TOP mRNAs, nor was there a redistribution of 5′TOP mRNAs from polysomes to nonpolysomes in the presence of rapamycin (24). However, S6 phosphorylation was initially reported to be abolished in these cells (24), despite the fact that it was largely intact in cells and tissues derived from S6K1−/− mice (51). This difference seemed to be resolved in subsequent studies, where S6 phosphorylation was detected in these same S6K1−/− ES cells and S6K2 was present and active (31, 60). Despite these observations, it was again recently reported that S6 phosphorylation was absent from these same cells (53). Furthermore, it was also claimed in the latter study that S6K activation, S6 phosphorylation, and rapamycin had little impact on 5′TOP mRNA translation in PC12 cells (53), although others working with these same cells had reported earlier that rapamycin treatment abolished the selective recruitment of these transcripts from small to large polysomes (44).
Obviously, cells lacking both S6K1 and S6K2 would facilitate such studies. Therefore, we set out to delete the S6K2 gene from mice and to determine whether we could generate S6K1−/−/S6K2−/− mice. Here we report on the deletion of the S6K2 gene and the effects of deleting both S6K1 and S6K2 on animal growth and viability as well as on S6 phosphorylation, cell proliferation, and 5′TOP mRNA translation.
Journal Article•
TL;DR: In this article, the authors used oligonucleotide-based DNA microarrays to analyze transcriptional changes resulting from constitutive Ras signaling and found that Ras signaling leads to a significant induction of Interleukin-8 (IL-8) mRNA, which is accompanied by a corresponding increase in protein levels.
Abstract: 1749 Ras proteins are important regulators of cell proliferation and their constitutive activation is a key event in cancer development. To discover novel effector pathways that might contribute to the oncogenic properties of Ras, we used oligonucleotide-based DNA microarrays to analyze transcriptional changes resulting from constitutive Ras signaling. We performed the expression analyses with HeLa stable cell lines expressing activated RasG12→V transgenes under a tetracycline responsive promoter (Tet-Off™ Expression System). This system not only mediates tight on/off regulation of gene expression; it also permits the titration of protein levels on a single cell basis allowing the study of dose dependent aspects of gene activity. Ras signaling leads to a significant induction of Interleukin-8 (IL-8) mRNA, which is accompanied by a corresponding increase in protein levels. IL-8 is a chemotactic factor for leukocytes and closely associated with the initiation of an acute inflammatory response. Analysis of signal transduction pathways that link Ras to IL-8 up-regulation suggests a direct effect of Ras on the IL-8 promoter, mediated by the synergistic activation of both MAPK-cascades and the PI3K > NFκB pathway. In addition, the Ras-induced accumulation of IL-8 protein is dependent on the activation of p38 MAP-kinase through a post-transcriptional mechanism involving an increase in IL-8 mRNA stability. Investigation of the functional importance of IL-8 in the context of tumorigenesis shows that IL-8 plays a decisive role in RasV12-mediated acceleration of tumor growth in a nude mouse xenograft model. Ablation of IL-8 function is accompanied by a significant reduction in tumor size. This effect is not due to decreased cell proliferation rates, since we observe no change in the mitogenic index of tumors after inhibition of IL-8. However, tumors devoid of functional IL-8 show a marked reduction in vascularization accompanied by vast tissue necrosis. These observations can be correlated with an IL-8-mediated initiation of an early inflammatory reaction in developing neoplasms that triggers tumor vascularization. In addition, IL-8 may act directly to support angiogenesis by promoting endothelial cell proliferation and migration. These results provide a novel mechanism by which tumor cells harboring oncogenic Ras can appropriate inflammatory mediators to recruit immune cells to the tumor site and facilitate neo-angiogenesis, thus setting the stage for subsequent progression to malignancy.
TL;DR: In vivo treatment of tumors in C57BL/6 and BALB/c mice resulted in significant slowing of tumor growth and extensive destruction of tumor cells within 3-6 days, demonstrating the potential applicability of the described electric fields as a novel therapeutic modality for malignant tumors.
Abstract: Low-intensity, intermediate-frequency (100–300 kHz), alternating electric fields, delivered by means of insulated electrodes, were found to have a profound inhibitory effect on the growth rate of a variety of human and rodent tumor cell lines (Patricia C, U-118, U-87, H-1299, MDA231, PC3, B16F1, F-98, C-6, RG2, and CT-26) and malignant tumors in animals. This effect, shown to be nonthermal, selectively affects dividing cells while quiescent cells are left intact. These fields act in two modes: arrest of cell proliferation and destruction of cells while undergoing division. Both effects are demonstrated when such fields are applied for 24 h to cells undergoing mitosis that is oriented roughly along the field direction. The first mode of action is manifested by interference with the proper formation of the mitotic spindle, whereas the second results in rapid disintegration of the dividing cells. Both effects, which are frequency dependent, are consistent with the computed directional forces exerted by these specific fields on charges and dipoles within the dividing cells. In vivo treatment of tumors in C57BL/6 and BALB/c mice (B16F1 and CT-26 syngeneic tumor models, respectively), resulted in significant slowing of tumor growth and extensive destruction of tumor cells within 3–6 days. These findings demonstrate the potential applicability of the described electric fields as a novel therapeutic modality for malignant tumors.
TL;DR: It is provocatively suggested that adult cancer results from rounds of disordered and unscheduled necrotic cell death, subsequent epithelial proliferation and the resulting suppressed immunity, rather than from a process that is dictated solely by cell growth.
Abstract: In children, cancer probably arises from a combination of inherited genetic mutations and genetic alterations that are acquired during the rapid cellular expansion that occurs during embryogenesis, and it is rarely associated with immune cell infiltrates. Conversely, in adults, cancer is frequently preceded by a long period of subclinical inflammatory disease and micronecrosis that provides a setting in which the epigenetic regulation of genes, cell death, cell proliferation and mutagenesis occurs. Here, we provocatively suggest that adult cancer results from rounds of disordered and unscheduled necrotic cell death, subsequent epithelial proliferation and the resulting suppressed immunity, rather than from a process that is dictated solely by cell growth. This paradigm shift regarding the development of cancer and this 'sixth sense' of the immune system indicates new strategies for cancer prevention and therapy.
TL;DR: Deletion of the C-terminal six amino acids of mTOR, which are essential for kinase activity, resulted in reduced cell size and proliferation arrest in embryonic stem cells, and showed that mTOR controls both cell Size and proliferation in early mouse embryos and embryonicstem cells.
Abstract: TOR is a serine-threonine kinase that was originally identified as a target of rapamycin in Saccharomyces cerevisiae and then found to be highly conserved among eukaryotes. In Drosophila melanogaster, inactivation of TOR or its substrate, S6 kinase, results in reduced cell size and embryonic lethality, indicating a critical role for the TOR pathway in cell growth control. However, the in vivo functions of mammalian TOR (mTOR) remain unclear. In this study, we disrupted the kinase domain of mouse mTOR by homologous recombination. While heterozygous mutant mice were normal and fertile, homozygous mutant embryos died shortly after implantation due to impaired cell proliferation in both embryonic and extraembryonic compartments. Homozygous blastocysts looked normal, but their inner cell mass and trophoblast failed to proliferate in vitro. Deletion of the C-terminal six amino acids of mTOR, which are essential for kinase activity, resulted in reduced cell size and proliferation arrest in embryonic stem cells. These data show that mTOR controls both cell size and proliferation in early mouse embryos and embryonic stem cells.
TL;DR: It is found that MM cells are irreversibly committed to cell death within few hours of incubation with SAHA, which highlights the pleiotropic antitumor effects of HDAC inhibition, and provides the framework for future clinical applications of SAHA to improve patient outcome in MM.
Abstract: Histone deacetylases (HDACs) affect cell growth at the transcriptional level by regulating the acetylation status of nucleosomal histones. HDAC inhibition induces differentiation and/or apoptosis in transformed cells. We recently showed that HDAC inhibitors, such as suberoylanilide hydroxamic acid (SAHA), potently induce apoptosis of human multiple myeloma (MM) cells. In this study, we focused on MM as a model to study the transcriptional profile of HDAC inhibitor treatment on tumor cells and to address their pathophysiological implications with confirmatory mechanistic and functional assays. We found that MM cells are irreversibly committed to cell death within few hours of incubation with SAHA. The molecular profile of MM cells before their commitment to SAHA-induced cell death is hallmarked by a constellation of antiproliferative and/or proapoptotic molecular events, including down-regulation of transcripts for members of the insulin-like growth factor (IGF)/IGF-1 receptor (IGF-1R) and IL-6 receptor (IL-6R) signaling cascades, antiapoptotic molecules (e.g., caspase inhibitors), oncogenic kinases, DNA synthesis/repair enzymes, and transcription factors (e.g., XBP-1, E2F-1) implicated in MM pathophysiology. Importantly, SAHA treatment suppresses the activity of the proteasome and expression of its subunits, and enhances MM cell sensitivity to proteasome inhibition by bortezomib (PS-341). SAHA also enhances the anti-MM activity of other proapoptotic agents, including dexamethasone, cytotoxic chemotherapy, and thalidomide analogs. These findings highlight the pleiotropic antitumor effects of HDAC inhibition, and provide the framework for future clinical applications of SAHA to improve patient outcome in MM.
TL;DR: HKI-272 is a potent inhibitor ofHER-2 and is highly active against HER-2-overexpressing human breast cancer cell lines in vitro and in vivo, and has been selected as a candidate for additional development as an antitumor agent in breast and other HER- 2-dependent cancers.
Abstract: HER-2 belongs to the ErbB family of receptor tyrosine kinases, which has been implicated in a variety of cancers. Overexpression of HER-2 is seen in 25-30% of breast cancer patients and predicts a poor outcome in patients with primary disease. Trastuzumab (Herceptin), a monoclonal antibody to HER-2, is specifically approved for HER-2-positive breast cancer but is active only in a subset of these tumors. Blocking HER-2 function by a small molecule kinase inhibitor, therefore, represents an attractive alternate strategy to inhibit the growth of HER-2-positive tumors. HKI-272 is a potent inhibitor of HER-2 and is highly active against HER-2-overexpressing human breast cancer cell lines in vitro. It also inhibits the epidermal growth factor receptor (EGFR) kinase and the proliferation of EGFR-dependent cells. HKI-272 reduces HER-2 receptor autophosphorylation in cells at doses consistent with inhibition of cell proliferation and functions as an irreversible binding inhibitor, most likely by targeting a cysteine residue in the ATP-binding pocket of the receptor. In agreement with the predicted effects of HER-2 inactivation, HKI-272 treatment of cells results in inhibition of downstream signal transduction events and cell cycle regulatory pathways. This leads to arrest at the G(1)-S (Gap 1/DNA synthesis)-phase transition of the cell division cycle, ultimately resulting in decreased cell proliferation. In vivo, HKI-272 is active in HER-2- and EGFR-dependent tumor xenograft models when dosed orally on a once daily schedule. On the basis of its favorable preclinical pharmacological profile, HKI-272 has been selected as a candidate for additional development as an antitumor agent in breast and other HER-2-dependent cancers.
TL;DR: It is demonstrated that HIF‐1α induces cell cycle arrest by functionally counteracting Myc, thereby derepressing p21cip1, and proposed that Myc is an integral part of a novel HIF-1α pathway, which regulates a distinct group of Myc target genes in response to hypoxia.
Abstract: Hypoxia induces angiogenesis and glycolysis for cell growth and survival, and also leads to growth arrest and apoptosis. HIF-1α, a basic helix–loop–helix PAS transcription factor, acts as a master regulator of oxygen homeostasis by upregulating various genes under low oxygen tension. Although genetic studies have indicated the requirement of HIF-1α for hypoxia-induced growth arrest and activation of p21cip1, a key cyclin-dependent kinase inhibitor controlling cell cycle checkpoint, the mechanism underlying p21cip1 activation has been elusive. Here we demonstrate that HIF-1α, even in the absence of hypoxic signal, induces cell cycle arrest by functionally counteracting Myc, thereby derepressing p21cip1. The HIF-1α antagonism is mediated by displacing Myc binding from p21cip1 promoter. Neither HIF-1α transcriptional activity nor its DNA binding is essential for cell cycle arrest, indicating a divergent role for HIF-1α. In keeping with its antagonism of Myc, HIF-1α also downregulates Myc-activated genes such as hTERT and BRCA1. Hence, we propose that Myc is an integral part of a novel HIF-1α pathway, which regulates a distinct group of Myc target genes in response to hypoxia.
TL;DR: It is shown that apoptotic cells express the secretory factors wingless (wg) and decapentaplegic (dpp) and that the DIAP1 antagonists reaper and hid can activate the JNK pathway and that this pathway is required for inducing wg and cell proliferation.
TL;DR: The findings show clear links between each PPAR isotype and carcinogenesis and what is the relevance of these findings to human pathology and therapy?
Abstract: Peroxisome-proliferator-activated receptors (PPARs) are nuclear hormone receptors that mediate the effects of fatty acids and their derivatives at the transcriptional level Through these pathways, PPARs can regulate cell proliferation, differentiation and survival, so controlling carcinogenesis in various tissues But what are the links between each PPAR isotype and carcinogenesis and what is the relevance of these findings to human pathology and therapy?
TL;DR: Senescence of CSCs and myocytes conditions the development of an aging myopathy, and IGF-1 enhanced nuclear phospho-Akt and telomerase delaying cellular aging and death.
Abstract: To determine whether cellular aging leads to a cardiomyopathy and heart failure, markers of cellular senescence, cell death, telomerase activity, telomere integrity, and cell regeneration were measured in myocytes of aging wild-type mice (WT). These parameters were similarly studied in insulin-like growth factor-1 (IGF-1) transgenic mice (TG) because IGF-1 promotes cell growth and survival and may delay cellular aging. Importantly, the consequences of aging on cardiac stem cell (CSC) growth and senescence were evaluated. Gene products implicated in growth arrest and senescence, such as p27Kip1, p53, p16INK4a, and p19ARF, were detected in myocytes of young WT mice, and their expression increased with age. IGF-1 attenuated the levels of these proteins at all ages. Telomerase activity decreased in aging WT myocytes but increased in TG, paralleling the changes in Akt phosphorylation. Reduction in nuclear phospho-Akt and telomerase resulted in telomere shortening and uncapping in WT myocytes. Senescence and death of CSCs increased with age in WT impairing the growth and turnover of cells in the heart. DNA damage and myocyte death exceeded cell formation in old WT, leading to a decreased number of myocytes and heart failure. This did not occur in TG in which CSC-mediated myocyte regeneration compensated for the extent of cell death preventing ventricular dysfunction. IGF-1 enhanced nuclear phospho-Akt and telomerase delaying cellular aging and death. The differential response of TG mice to chronological age may result from preservation of functional CSCs undergoing myocyte commitment. In conclusion, senescence of CSCs and myocytes conditions the development of an aging myopathy.
TL;DR: It is demonstrated that ERβ-selective estrogens may lack breast cancer promoting properties exhibited by estrogens in hormone replacement regimens and may be useful for chemoprevention of breast cancer.
Abstract: Studies indicate that estrogen receptor (ER) α mediates breast cancer-promoting effects of estrogens. The role of ERβ in breast cancer is unknown. Elucidating the role of ERβ in the pathogenesis of breast cancer is important because many human breast tumors express both ERα and ERβ. We show that adenovirus-mediated expression of ERβ changes the phenotype of ERα-positive MCF-7 cells. Estradiol increases cell proliferation and causes tumor formation of MCF-7 cells expressing only ERα. In contrast, introducing ERβ into MCF-7 cells causes an inhibition of proliferation in vitro and prevents tumor formation in a mouse xenograft model in response to estradiol. ERβ inhibits proliferation by repressing c-myc, cyclin D1, and cyclin A gene transcription, and increasing the expression of p21Cip1 and p27Kip1, which leads to a G2 cell cycle arrest. These results demonstrate that ERα and ERβ produce opposite effects in MCF-7 cells on cell proliferation and tumor formation. Natural or synthetic ERβ-selective estrogens may lack breast cancer promoting properties exhibited by estrogens in hormone replacement regimens and may be useful for chemoprevention of breast cancer.
TL;DR: This article showed that glucagon-like peptides (GLP-1 and GLP-2) directly regulate signaling pathways coupled to cell proliferation and apoptosis, which may be mediated by direct or indirect effects on target cells.
Abstract: Gut peptides exert diverse effects regulating satiety, gastrointestinal motility and acid secretion, epithelial integrity, and both nutrient absorption and disposal. These actions are initiated by activation of specific G protein-coupled receptors and may be mediated by direct or indirect effects on target cells. More recent evidence demonstrates that gut peptides, exemplified by glucagon-like peptides-1 and 2 (GLP-1 and GLP-2), directly regulate signaling pathways coupled to cell proliferation and apoptosis. GLP-1 receptor activation enhances beta-cell proliferation and promotes islet neogenesis via activation of pdx-1 expression. The proliferative effects of GLP-1 appear to involve multiple intracellular pathways, including stimulation of Akt, activation of protein kinase Czeta, and transactivation of the epidermal growth factor receptor through the c-src kinase. GLP-1 receptor activation also promotes cell survival in beta-cells and neurons via increased levels of cAMP leading to cAMP response element binding protein activation, enhanced insulin receptor substrate-2 activity and, ultimately, activation of Akt. These actions of GLP-1 are reflected by expansion of beta-cell mass and enhanced resistance to beta-cell injury in experimental models of diabetes in vivo. GLP-2 also promotes intestinal cell proliferation and confers resistance to cellular injury in a variety of cell types. Administration of GLP-2 to animals with experimental intestinal injury promotes regeneration of the gastrointestinal epithelial mucosa and confers resistance to apoptosis in an indirect manner via yet-to-be identified GLP-2 receptor-dependent regulators of mucosal growth and cell survival. These proliferative and antiapoptotic actions of GLP-1 and GLP-2 may contribute to protective and regenerative actions of these peptides in human subjects with diabetes and intestinal disorders, respectively.
TL;DR: It is shown that muscles of juvenile Pax7(−/−) mice at P11 contain a reduced but substantial number of satellite cells, indicating an essential function of Pax7 for renewal and maintenance of muscle stem cells and exclude an exclusive role of Pax8 in satellite cell specification.
Abstract: The paired-box transcription factor Pax7 has been claimed to specify the muscle stem cell lineage since inactivation of Pax7 led to a failure to detect muscle satellite cells. Here we show that muscles of juvenile Pax7(−/−) mice at P11 contain a reduced but substantial number of satellite cells. Neither juvenile nor adult Pax7(−/−) mice displayed a significant reduction in the number and size of myotubes, indicating that the remaining number of satellite cells sufficed to allow normal postnatal muscle growth. The number of satellite cells in Pax7 mutant mice declined strongly during postnatal development, although single satellite cells were readily identified in adult Pax7 mutant mice. Muscle regeneration was impaired in adult Pax7 mutant mice. Our results clearly indicate an essential function of Pax7 for renewal and maintenance of muscle stem cells and exclude an exclusive role of Pax7 in satellite cell specification.
TL;DR: The current state of knowledge on the mode of action of minoxidil on hair growth is reviewed, and lines of future research are indicated that may be relevant to hair growth.
Abstract: Summary
We have known for over 30 years that minoxidil stimulates hair growth, yet our understanding of its mechanism of action on the hair follicle is very limited. In animal studies, topical minoxidil shortens telogen, causing premature entry of resting hair follicles into anagen, and it probably has a similar action in humans. Minoxidil may also cause prolongation of anagen and increases hair follicle size. Orally administered minoxidil lowers blood pressure by relaxing vascular smooth muscle through the action of its sulphated metabolite, minoxidil sulphate, as an opener of sarcolemmal KATP channels. There is some evidence that the stimulatory effect of minoxidil on hair growth is also due to the opening of potassium channels by minoxidil sulphate, but this idea has been difficult to prove and to date there has been no clear demonstration that KATP channels are expressed in the hair follicle. A number of in vitro effects of minoxidil have been described in monocultures of various skin and hair follicle cell types including stimulation of cell proliferation, inhibition of collagen synthesis, and stimulation of vascular endothelial growth factor and prostaglandin synthesis. Some or all of these effects may be relevant to hair growth, but the application of results obtained in cell culture studies to the complex biology of the hair follicle is uncertain. In this article we review the current state of knowledge on the mode of action of minoxidil on hair growth and indicate lines of future research.
TL;DR: The mTOR gene is disrupted and embryonic development of homozygous mTOR − / − mice appears to be arrested at E5.5; such embryos are severely runted and display an aberrant developmental phenotype, consistent with the inability to establish embryonic stem cells from mTOR +/ − embryos.
Abstract: The mammalian target of rapamycin (mTOR) is a key component of a signaling pathway which integrates inputs from nutrients and growth factors to regulate cell growth. Recent studies demonstrated that mice harboring an ethylnitrosourea-induced mutation in the gene encoding mTOR die at embryonic day 12.5 (E12.5). However, others have shown that the treatment of E4.5 blastocysts with rapamycin blocks trophoblast outgrowth, suggesting that the absence of mTOR should lead to embryonic lethality at an earlier stage. To resolve this discrepancy, we set out to disrupt the mTOR gene and analyze the outcome in both heterozygous and homozygous settings. Heterozygous mTOR (mTOR(+/-)) mice do not display any overt phenotype, although mouse embryonic fibroblasts derived from these mice show a 50% reduction in mTOR protein levels and phosphorylation of S6 kinase 1 T389, a site whose phosphorylation is directly mediated by mTOR. However, S6 phosphorylation, raptor levels, cell size, and cell cycle transit times are not diminished in these cells. In contrast to the situation in mTOR(+/-) mice, embryonic development of homozygous mTOR(-/-) mice appears to be arrested at E5.5; such embryos are severely runted and display an aberrant developmental phenotype. The ability of these embryos to implant corresponds to a limited level of trophoblast outgrowth in vitro, reflecting a maternal mRNA contribution, which has been shown to persist during preimplantation development. Moreover, mTOR(-/-) embryos display a lesion in inner cell mass proliferation, consistent with the inability to establish embryonic stem cells from mTOR(-/-) embryos.
TL;DR: In this paper, it was shown that high omega-6/omega-3 ratio promotes pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases, whereas increased levels of omega-3 PUFA exert suppressive effects.
Abstract: Several sources of information suggest that human beings evolved on a diet with a ratio of omega-6 to omega-3 essential fatty acids (EFA) of ∼1 whereas in Western diets the ratio is 15/1–16.7/1. Western diets are deficient in omega-3 fatty acids, and have excessive amounts of omega-6 fatty acids compared with the diet on which human beings evolved and their genetic patterns were established. Excessive amounts of omega-6 polyunsaturated fatty acids (PUFA) and a very high omega-6/omega-3 ratio, as is found in today's Western diets, promote the pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases, whereas increased levels of omega-3 PUFA (a lower omega-6/omega-3 ratio), exert suppressive effects. In the secondary prevention of cardiovascular disease, a ratio of 4/1 was associated with a 70% decrease in total mortality. A ratio of 2.5/1 reduced rectal cell proliferation in patients with colorectal cancer, whereas a ratio of 4/1 with the sam...
TL;DR: The hypothesis that certain breast cancer cells rely on NF-κB for aberrant cell proliferation and simultaneously avoid apoptosis is substantiated, thus implicating activated NF-kkB as a therapeutic target for distinctive subclasses of ER-negative breast cancers.
Abstract: Lack of molecular targets in estrogen receptor-negative (ER-negative) breast cancer is a major therapeutic hurdle. We studied NF-κB activation in human breast tumors and in carcinoma cell lines. Activated NF-κB was detected predominantly in ER-negative vs. ER-positive breast tumors and mostly in ER-negative and ErbB2-positive tumors (86%). These in vivo results demonstrate association of activated NF-κB with a subgroup of human breast tumors and are consistent with previously reported in vitro observations using similar classes of human breast cancer cell lines. Finding such an association suggested functional and biological significance. Immunofluorescence demonstrated increased nuclear p65, a component of the active NF-κB complex, in cytokeratin 19 (CK19)-positive epithelial cells of ER-negative/ErbB2-positive tumor samples. In contrast, nuclear NF-κB was detected mostly in stroma of ER-negative and ErbB2-negative tumors, suggesting a role of activated NF-κB in intercellular signaling between epithelial and stromal cells in this type of breast cancers. To elucidate roles of activated NF-κB, we used an ER-negative and ErbB2-positive human breast tumor cell line (SKBr3). The polypeptide heregulin β1 stimulated, and herceptin, the anti-ErbB2 antibody, inhibited, NF-κB activation in SKBr3 cells. The NF-κB essential modulator (NEMO)-binding domain (NBD) peptide, an established selective inhibitor of IκB-kinase (IKK), blocked heregulin-mediated activation of NF-κB and cell proliferation, and simultaneously induced apoptosis only in proliferating and not resting cells. These results substantiate the hypothesis that certain breast cancer cells rely on NF-κB for aberrant cell proliferation and simultaneously avoid apoptosis, thus implicating activated NF-κB as a therapeutic target for distinctive subclasses of ER-negative breast cancers.