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Showing papers on "Cell growth published in 1995"


Journal ArticleDOI
10 Mar 1995-Science
TL;DR: In multicellular organisms, homeostasis is maintained through a balance between cell proliferation and cell death, and recent evidence suggests that alterations in cell survival contribute to the pathogenesis of a number of human diseases.
Abstract: In multicellular organisms, homeostasis is maintained through a balance between cell proliferation and cell death. Although much is known about the control of cell proliferation, less is known about the control of cell death. Physiologic cell death occurs primarily through an evolutionarily conserved form of cell suicide termed apoptosis. The decision of a cell to undergo apoptosis can be influenced by a wide variety of regulatory stimuli. Recent evidence suggests that alterations in cell survival contribute to the pathogenesis of a number of human diseases, including cancer, viral infections, autoimmune diseases, neurodegenerative disorders, and AIDS (acquired immunodeficiency syndrome). Treatments designed to specifically alter the apoptotic threshold may have the potential to change the natural progression of some of these diseases.

6,462 citations


Journal ArticleDOI
10 Nov 1995-Science
TL;DR: Although CTLA-4-deficient T cells proliferated spontaneously and strongly when stimulated through the T cell receptor, they were sensitive to cell death induced by cross-linking of the Fas receptor and by gamma irradiation, and is vital for the control of lymphocyte homeostasis.
Abstract: The role of the cell-surface molecule CTLA-4 in the regulation of T cell activation has been controversial. Here, lymph nodes and spleens of CTLA-4-deficient mice accumulated T cell blasts with up-regulated activation markers. These blast cells also infiltrated liver, heart, lung, and pancreas tissue, and amounts of serum immunoglobulin were elevated. The mice invariably became moribund by 3 to 4 weeks of age. Although CTLA-4-deficient T cells proliferated spontaneously and strongly when stimulated through the T cell receptor, they were sensitive to cell death induced by cross-linking of the Fas receptor and by gamma irradiation. Thus, CTLA-4 acts as a negative regulator of T cell activation and is vital for the control of lymphocyte homeostasis.

2,742 citations


Journal ArticleDOI
TL;DR: Data show that metastases remain dormant when tumour cell proliferation is balanced by an equivalent rate of cell death and suggest that angiogenesis inhibitors control metastatic growth by indirectly increasing apoptosis in tumour cells.
Abstract: In cancer patients, dormant micrometastases are often asymptomatic and clinically undetectable, for months or years, until relapse. We have studied dormant lung metastases under angiogenesis suppression in mice. The metastases exhibited rapid growth when the inhibition of angiogenesis was removed. Tumour cell proliferation, as measured by bromodeoxyuridine incorporation and immunohistochemical staining proliferating cell nuclear antigen, was not significantly different in dormant and growing metastases. However, tumour cells of dormant metastases exhibited a more than threefold higher incidence of apoptosis. These data show that metastases remain dormant when tumour cell proliferation is balanced by an equivalent rate of cell death and suggest that angiogenesis inhibitors control metastatic growth by indirectly increasing apoptosis in tumour cells.

1,859 citations


Journal ArticleDOI
23 Feb 1995-Nature
TL;DR: It is reported that mice lacking SF/HGF fail to complete development and die in utero, and the mutation affects the embryonic liver, which is reduced in size and shows extensive loss of parenchymal cells.
Abstract: Polypeptide growth factors are important effectors of cell growth and differentiation in vitro and are thought to be critical for processes such as specification of cell fate, tissue growth and organogenesis in vivo. Scatter factor/hepatocyte growth factor (SF/HGF) is the prototype of an emerging family of growth factors that resemble in their domain structure and mechanism of activation the blood proteinase plasminogen. The cellular responses of SF/HGF are mediated by the c-Met tyrosine kinase receptor. Here we report that mice lacking SF/HGF fail to complete development and die in utero. The mutation affects the embryonic liver, which is reduced in size and shows extensive loss of parenchymal cells. In addition, development of the placenta, particularly of trophoblast cells, is impaired. Thus, SF/HGF is essential for the development of several epithelial organs.

1,405 citations


Journal ArticleDOI
01 Jul 1995-Immunity
TL;DR: Data demonstrating that CD28 costimulation enhances the in vitro survival of activated T cells and suggesting that an important role of CD28costimulation is to augment T cell survival during antigen activation is suggested.

1,245 citations


Journal ArticleDOI
TL;DR: A wide variety of normal and malignant cell types generate and release superoxide or hydrogen peroxide in vitro either in response to specific cytokine/growth factor stimulus or constitutively in the case of tumour cells.

1,185 citations


Journal ArticleDOI
TL;DR: It is shown that normal tissue expression of p21 to high levels is not dependent on p53 and confirm that induction of p23 by DNA-damaging agents does require p53, and p53 appears to play a critical role in p21 induction following DNA damage.
Abstract: Expression of p21 has been shown to be up-regulated by the p53 tumor suppressor gene in vitro in response to DNA-damaging agents. However, p21 expression can be regulated independently of p53, and here we show that expression of p21 in various tissues during development and in the adult mouse occurs in the absence of p53 function. However, most tissues tested did require p53 for p21 induction following exposure of the whole animal to gamma irradiation. These results show that normal tissue expression of p21 to high levels is not dependent on p53 and confirm that induction of p21 by DNA-damaging agents does require p53. p21 is expressed upon differentiation of p53-deficient murine erythroleukemia (MEL) cells, and the kinetics of induction of p21 in this system suggest that it may be involved in the growth arrest that precedes terminal differentiation. The gene is up-regulated in mouse fibroblasts in response to serum restimulation but the kinetics and levels of induction differ between wild-type and mutant cells. Expression of p21 message following serum restimulation is superinducible by cycloheximide in wild-type but not in p53-deficient cells. The increases in p21 mRNA are reflected in changes in p21 protein levels. p21 expression also appears to be regulated at the post-transcriptional level because moderate increases in mRNA expression, during differentiation of MEL cells and upon serum restimulation of fibroblasts, are followed by large increases in protein levels. Regulation of the mouse p21 promoter by p53 depends on two critical p53-binding sites located 1.95 and 2.85 kb upstream from the transcriptional initiation site. The sequences mediating serum responsiveness of the promoter map to a region containing the proximal p53 site. p53 appears to play a critical role in p21 induction following DNA damage. Moreover, p21 can be regulated independently of p53 in several situations including during normal tissue development, following serum stimulation, and during cellular differentiation.

1,098 citations


Journal ArticleDOI
17 Feb 1995-Science
TL;DR: The expression pattern of mouse p21 correlated with terminal differentiation of multiple cell lineages including skeletal muscle, cartilage, skin, and nasal epithelium in a p53-independent manner, demonstrating that p21 expression does not require these transcription factors.
Abstract: Terminal differentiation is coupled to withdrawal from the cell cycle. The cyclin-dependent kinase inhibitor (CKI) p21Cip1 is transcriptionally regulated by p53 and can induce growth arrest. CKIs are therefore potential mediators of developmental control of cell proliferation. The expression pattern of mouse p21 correlated with terminal differentiation of multiple cell lineages including skeletal muscle, cartilage, skin, and nasal epithelium in a p53-independent manner. Although the muscle-specific transcription factor MyoD is sufficient to activate p21 expression in 10T1/2 cells, p21 was expressed in myogenic cells of mice lacking the genes encoding MyoD and myogenin, demonstrating that p21 expression does not require these transcription factors. The p21 protein may function during development as an inducible growth inhibitor that contributes to cell cycle exit and differentiation.

1,082 citations


Journal ArticleDOI
27 Jul 1995-Nature
TL;DR: It is found that EGF-R-/- mice survive for up to 8 days after birth and suffer from impaired epithelial development in several organs, including skin, lung and gastrointestinal tract.
Abstract: Since the discovery that epidermal growth factor (EGF) can accelerate opening of the eyelids, the EGF receptor (EGF-R) has been extensively studied and is now considered to be a prototype tyrosine kinase receptor. Binding of EGF or of transforming growth factor-alpha (TGF-alpha) or other related factors activates the receptor and induces cell proliferation and differentiation. Although it is not found on haematopoietic cells, the EGF-R is widely expressed in mammals and has been implicated in various stages of embryonic development. Here we investigate the developmental and physiological roles of this receptor and its ligands by inactivating the gene encoding EGF-R. We find that EGF-R-/- mice survive for up to 8 days after birth and suffer from impaired epithelial development in several organs, including skin, lung and gastrointestinal tract.

1,036 citations


Journal ArticleDOI
TL;DR: The results show that the growth modulating actions of ANG II depend on the type of angiotensin receptor present on a given cell, and in coronary endothelial cells, the antiproliferative actions of the AT2-receptor offset the growth promoting effects mediated by the AT1- receptor.
Abstract: Angiotensin II (ANG II) is known to be a potent growth promoting factor for vascular smooth muscle cells and fibroblasts but little is known about its influence on growth in endothelial cells. We studied the effects of ANG II on endothelial growth and the role of the angiotensin receptor subtypes involved. Proliferation of rat coronary endothelial cells (CEC) and rat vascular smooth muscle cells (VSMC) was determined by [3H]thymidine incorporation, the MTT-test and by directly counting cells in a coulter counter. Angiotensin AT1- and AT2-receptors were demonstrated by binding studies and by the presence of their respective mRNA through reverse transcription polymerase chain reaction (RT-PCR). In contrast to VSMC, which in culture only express the AT1-receptor, CEC express both, AT1- and AT2-receptors simultaneously up to the third passage. Whereas ANG II stimulated growth of quiescent VSMC, an effect abolished by pretreatment with the AT1-receptor antagonist, losartan, ANG II did not induce proliferation in quiescent CEC. However, after pretreatment of quiescent endothelial cells (< passage 4) with the AT2-receptor antagonist, PD 123177, ANG II induced proliferation. This effect was reversed by additional pretreatment with losartan. ANG II significantly inhibited the proliferation of bFGF-stimulated CEC in a dose-dependent manner by maximally 50%. This effect was prevented by PD 123177 while losartan was ineffective. The AT2-receptor agonist, CGP 42112, mimicked the antiproliferative actions of ANG II, confirming the specificity of the effect. Our results show that the growth modulating actions of ANG II depend on the type of angiotensin receptor present on a given cell. In coronary endothelial cells, the antiproliferative actions of the AT2-receptor offset the growth promoting effects mediated by the AT1-receptor.

917 citations


Journal ArticleDOI
TL;DR: The results strongly suggest that the FKBP12-rapamycin complex interacts with homologous ligands in yeast and mammalian cells and that the loss of mTOR function is directly related to the inhibitory effect of rapamycin on G1- to S-phase progression in T-lymphocytes and other sensitive cell types.

Journal ArticleDOI
TL;DR: It is suggested that rapamycin, but not FK520, inhibits vascular smooth muscle cell proliferation by reducing cell-cycle kinase activity.
Abstract: Multiple growth factors can stimulate quiescent vascular smooth muscle cells to exit from G0 and reenter the cell cycle. The macrolide antibiotic rapamycin, bound to its cytosolic receptor FKBP, is an immunosuppressant and a potent inhibitor of cellular proliferation. In the present study, the antiproliferative effects of rapamycin on human and rat vascular smooth muscle cells were examined and compared with the effects of a related immunosuppressant, FK520. In vascular smooth muscle cells, rapamycin, at concentrations as low as 1 ng/mL, inhibited DNA synthesis and cell growth. FK520, an analogue of the immunosuppressant FK506, is structurally related to rapamycin and binds to FKBP but did not inhibit vascular smooth muscle cell growth. Molar excesses of FK520 blocked the antiproliferative effects of rapamycin, indicating that the effects of rapamycin required binding to FKBP. Rapamycin-FKBP inhibited retinoblastoma protein phosphorylation at the G1/S transition. This inhibition of retinoblastoma protein phosphorylation was associated with a decrease in p33cdk2 kinase activity. These observations suggest that rapamycin, but not FK520, inhibits vascular smooth muscle cell proliferation by reducing cell-cycle kinase activity.

Journal ArticleDOI
TL;DR: It is proposed that after partial hepatectomy, hepatocytes enter a state of replicative competence (“priming”) before they can fully respond to growth factors and the activity of stimulatory and inhibitory growth factors is low in normal livers but that the expression of both types of factors increase during liver regeneration.
Abstract: During liver regeneration quiescent hepatocytes undergo one or two rounds of replication and then return to a nonproliferative state. Growth factors regulate this process by providing both stimulatory and inhibitory signals for cell proliferation. EGF, TGF alpha, and HGF stimulate DNA synthesis in hepatocytes in vivo and in culture but the sensitivity of cultured hepatocytes to the mitogenic effects of these factors is much higher than that of quiescent hepatocytes in intact livers. We have proposed that after partial hepatectomy, hepatocytes enter a state of replicative competence ("priming") before they can fully respond to growth factors. The priming step is an initiating event in liver regeneration that involves the activation and DNA binding of NF-kappa B and other transcription factors, which could be induced by TNF or other cytokines. EGF, TGF alpha, and HGF have major effects on liver growth. TGF alpha expression correlates with hepatocyte DNA synthesis during liver development and growth and the constitutive expression of the factor confers proliferative activity to adult hepatocytes in vivo and in culture. The data indicate that the activity of stimulatory and inhibitory growth factors such as TGF beta 1 and activin is low in normal livers but that the expression of both types of factors increase during liver regeneration.

Journal ArticleDOI
TL;DR: It is suggested that BRCA1 may normally serve as a negative regulator of mammary epithelial cell growth whose function is compromised in breast cancer either by direct mutation or alterations in gene expression.
Abstract: We have characterized expression of the familial breast and ovarian cancer gene, BRCA1, in cases of non-hereditary (sporadic) breast cancer and analyzed the effect of antisense inhibition of BRCA1 on the proliferative rate of mammary epithelial cells. BRCA1 mRNA levels are markedly decreased during the transition from carcinoma in situ to invasive cancer. Experimental inhibition of BRCA1 expression with antisense oligonucleotides produced accelerated growth of normal and malignant mammary cells, but had no effect on non-mammary epithelial cells. These studies suggest that BRCA1 may normally serve as a negative regulator of mammary epithelial cell growth whose function is compromised in breast cancer either by direct mutation or alterations in gene expression.

Journal ArticleDOI
TL;DR: It is demonstrated that both TNFα and bFGF induce ROS production, and that this is a common signaling event involved in the stimulation of c-fos gene expression in chondrocytes, the first report directly demonstrating ROS production upon stimulation with a growth factor.

Journal ArticleDOI
TL;DR: In addition to its inhibitory effect on basal endometrial cancer cell proliferation, lycopene also suppressed insulin-like growth factor-I-stimulated growth, which are major autocrine/paracrine regulators of mammary and endometrian cancer cell growth.
Abstract: The antiproliferative properties of lycopene, the major tomato carotenoid, were compared with those of alpha- and beta-carotene. Lycopene, delivered in cell culture medium from stock solutions in tetrahydrofuran, strongly inhibited proliferation of endometrial (Ishikawa), mammary (MCF-7), and lung (NCI-H226) human cancer cells with half-maximal inhibitory concentration of 1-2 microM; alpha- and beta-carotene were far less effective inhibitors. For example, in Ishikawa cells, a 4-fold higher concentration of alpha-carotene or a 10-fold higher concentration of beta-carotene was needed for the same order of growth suppression. The inhibitory effect of lycopene was detected after 24 hours of incubation, and it was maintained for at least three days. In contrast to cancer cells, human fibroblasts were less sensitive to lycopene, and the cells gradually escaped growth inhibition over time. In addition to its inhibitory effect on basal endometrial cancer cell proliferation, lycopene also suppressed insulin-like growth factor-I-stimulated growth. Insulin-like growth factors are major autocrine/paracrine regulators of mammary and endometrial cancer cell growth. Therefore, lycopene interference in this major autocrine/paracrine system may open new avenues for research on the role of lycopene in the regulation of endometrial cancer and other tumors.

Journal ArticleDOI
TL;DR: The role of calcium in cell proliferation is highlighted by the increasing number of anticancer therapies and immunosuppressant drugs directed towards this calcium signalling pathway.
Abstract: The orderly sequence of events that constitutes the cell cycle is carefully regulated. A part of this regulation depends upon the ubiquitous calcium signalling system. Many growth factors utilize the messenger inositol trisphosphate (InsP3) to set up prolonged calcium signals, often organized in an oscillatory pattern. These repetitive calcium spikes require both the entry of external calcium and its release from internal stores. One function of this calcium signal is to activate the immediate early genes responsible for inducing resting cells (G0) to re-enter the cell cycle. It may also promote the initiation of DNA synthesis at the G1/S transition. Finally, calcium contributes to the completion of the cell cycle by stimulating events at mitosis. The role of calcium in cell proliferation is highlighted by the increasing number of anticancer therapies and immunosuppressant drugs directed towards this calcium signalling pathway.

Journal Article
TL;DR: The apoptotic response to sulindac sulfide and sulfone was both time- and dose-dependent and involved a mechanism independent of their inhibitory effect on cell cycle progression, suggesting that apoptosis is responsible for the cell growth inhibitory activity of sulindafiltration and represents a potential mechanism for the antineoplastic activity of these drugs.
Abstract: The nonsteroidal anti-inflammatory drug sulindac is known to inhibit chemical carcinogenesis in rodent models and cause regression of adenomas in patients with adenomatous polyposis coli. Sulindac is a prodrug that is metabolized to a pharmacologically active sulfide derivative that potently inhibits prostaglandin synthesis. Recent studies, however, have shown that a sulfone derivative of sulindac, which essentially lacks prostaglandin synthesis inhibitory activity, also inhibits chemical carcinogenesis, suggesting that reduction of prostaglandin levels is not necessary for the antineoplastic activity of this class of drugs. Both sulindac sulfide and the sulfone inhibit the growth of cultured tumor cells, although the cellular mechanism(s) responsible for the antineoplastic activity of sulindac derivatives is unknown. In this study, we investigated the effects of sulindac sulfide and sulfone on the proliferation, differentiation, and apoptosis of HT-29 human colon carcinoma cells. Sulindac sulfide and sulfone significantly reduced cell number in both preconfluent and confluent cultures of HT-29 cells with the sulfide showing approximately 4-fold greater potency. In addition to HT-29 cells, both drugs inhibited the growth of a variety of tumor cell lines derived from other tissues, as well as normal epithelial cells and fibroblasts. Neither sulindac sulfide nor sulfone inhibited cell proliferation under conditions where the drugs were growth inhibitory. Only under specific conditions involving mitogenic stimulation did sulindac sulfide and sulfone cause cell cycle arrest. Neither sulindac sulfide nor the sulfone induced differentiation of HT-29 cells, but both drugs strongly induced apoptosis. The apoptotic response to sulindac sulfide and sulfone was both time- and dose-dependent and involved a mechanism independent of their inhibitory effect on cell cycle progression. These data suggest that apoptosis is responsible for the cell growth inhibitory activity of sulindac sulfide and sulfone and represents a potential mechanism for the antineoplastic activity of these drugs.

Journal ArticleDOI
TL;DR: Evidence is found that apoptosis and cell proliferation coincide to some degree and the interleukin-1 beta converting enzyme (ICE) family of cysteine proteases is now known to play a key role in apoptosis but has no discernible role in the cell cycle, arguing that the two processes are discrete.

Journal ArticleDOI
TL;DR: The activation of the sphingomyelinase/ceramide pathway in HDF is due to senescence and supports the hypotheses that senescENCE represents a distinct program of cell development that can be differentiated from quiescence.

Journal ArticleDOI
TL;DR: Elucidation of the genetic and biochemical controls of these cellular responses may provide insights into ways to induce cell death and thus hopefully suggest new targets for improving therapeutic index in the treatment of malignancies.
Abstract: Cellular proliferation depends on the rates of both cell division and cell death. Tumors frequently have decreased cell death as a primary mode of increased cell proliferation. Genetic changes resulting in loss of programmed cell death (apoptosis) are likely to be critical components of tumorigenesis. Many of the gene products which appear to control apoptotic tendencies are regulators of cell cycle progression; thus, cell cycle control and cell death appear to be tightly linked processes. P53 protein is an example of a gene product which affects both cell cycle progression and apoptosis. The ability of p53 overexpression to induce apoptosis may be a major reason why tumor cells frequently disable p53 during the transformation process. Unfortunately, the same genetic changes which cause loss of apoptosis during tumor development, may also result in tumor cell resistance to anti-neoplastic therapies which kill tumor cells by apoptosis. Elucidation of the genetic and biochemical controls of these cellular responses may provide insights into ways to induce cell death and thus hopefully suggest new targets for improving therapeutic index in the treatment of malignancies.

Journal ArticleDOI
TL;DR: A mathematical model for the growth of a multicellular spheroid that comprises a central core of necrotic cells surrounded by an outer annulus of proliferating cells is presented in this article.
Abstract: A mathematical model is presented for the growth of a multicellular spheroid that comprises a central core of necrotic cells surrounded by an outer annulus of proliferating cells. The model distinguishes two mechanisms for cell loss: apoptosis and necrosis. Cell loss due to apoptosis is defined to be programmed cell death, occurring, for example, when a cell exceeds its natural lifespan, whereas cell death due to necrosis is induced by changes in the cell's microenvironment, occurring, for example, in nutrient-depleted regions. Mathematically, the problem involves tracking two free boundaries, one for the outer tumor radius, the other for the inner necrotic radius. Numerical simulations of the model are presented in an inhibitor-free setting and an inhibitor-present setting for various parameter values. The effects of nutrients and inhibitors on the existence and stability of the time-independent solutions of the model are studied using a combination of numerical and asymptotic techniques.

Journal ArticleDOI
TL;DR: It is shown that, in plants, the developmental controls defining shape can act independently from cell division rates, and Morphogenesis, histogenesis and developmental timing were unaffected.
Abstract: Because plant cells do not move and are surrounded by a rigid cell wall, cell division rates and patterns are believed to be directly responsible for generating new structures throughout development. To study the relationship between cell division and morphogenesis, transgenic tobacco and Arabidopsis plants were constructed expressing dominant mutations in a key regulator of the Arabidopsis cell cycle, the Cdc2a kinase. Plants constitutively overproducing the wild-type Cdc2a or the mutant form predicted to accelerate the cell cycle did not exhibit a significantly altered development. In contrast, a mutation expected to arrest the cell cycle abolished cell division when expressed in Arabidopsis, whereas some tobacco plants constitutively producing this mutant protein were recovered. These plants had a reduced histone H1 kinase activity and contained considerably fewer cells. These cells were, however, much larger and underwent normal differentiation. Morphogenesis, histogenesis and developmental timing were unaffected. The results indicate that, in plants, the developmental controls defining shape can act independently from cell division rates.

Journal ArticleDOI
TL;DR: E2F1 can induce events leading to S phase but that the process is not normal and appears to result from the activation of a cell death pathway, which leads to massive cell death that is characteristic of apoptosis.
Abstract: Various experiments have demonstrated a role for the E2F transcription factor in the regulation of cell growth during the G0/G1/S phase transition. Indeed, overexpression of the E2F1 product, a component of the cellular E2F activity, induces DNA synthesis in quiescent fibroblasts. To provide an approach to a more detailed biochemical analysis of these events, we have made use of a recombinant adenovirus containing the E2F1 cDNA in order to efficiently express the E2F1 product in an entire population of cells. We demonstrate an induction of DNA synthesis when quiescent cells are infected with the E2F1 recombinant virus. However, we also find that the induction does not lead to a complete replication of the cellular genome, as revealed by flow cytometry. The incomplete nature of cellular DNA replication is due, at least in part, to the fact that E2F1 overexpression leads to massive cell death that is characteristic of apoptosis. This E2F1-mediated induction of apoptosis is largely dependent on endogenous wild-type p53 activity and can be subverted by introducing mutant forms of p53 into these cells or by overexpressing E2F1 in fibroblasts derived from p53-null mouse embryos. We conclude that E2F1 can induce events leading to S phase but that the process is not normal and appears to result from the activation of a cell death pathway.

Journal Article
TL;DR: It is shown that in vivo neutralization of IL-12 eliminates the NK cell cytotoxic response and IFN-gamma production by lymph node cells from 2-day L. major-infected C3H mice, and that even when IL- 12 is induced, Th1 cell development may be interrupted by simultaneous production of inhibitory cytokines.
Abstract: Infection of mice with the protozoan Leishmania major is an established in vivo model for the definition of factors that contribute to CD4+ T helper cell subset development In the current study, a central role for IL-12 in directing both the innate and adaptive immune responses to L major is established We show that in vivo neutralization of IL-12 eliminates the NK cell cytotoxic response and IFN-gamma production by lymph node cells from 2-day L major-infected C3H mice Moreover, anti-IL-12 treatment abrogated Th1 cell development and enhanced Th2 cell development Consistent with these results, elevated IL-12 p40 production and an increase in the number of IL-12 p40-producing cells were observed within 1 day of infection in C3H mice Because BALB/c mice lack an early NK cell response or a Th1-type immune response after L major infection, we investigated the possibility that they had a defect in the ability to produce IL-12 Surprisingly, L major infection stimulated IL-12 p40 production in BALB/c mice early after infection Further studies suggest that BALB/c mice are unable to generate an early IFN-gamma response because of the simultaneous production of IL-12 and cytokines that inhibit IL-12 function, such as TGF-beta, IL-4, and IL-10 Together, these data show that IL-12 regulates the immune response to L major, but that even when IL-12 is induced, Th1 cell development may be interrupted by simultaneous production of inhibitory cytokines

Journal ArticleDOI
13 Jan 1995-Science
TL;DR: Ectopic expression of p16INK4 blocked entry into S phase of the cell cycle induced by oncogenic Ha-Ras, and this block was relieved by coexpression of a catalytically inactive CDK4 mutant, providing direct evidence that p16ink4 can inhibit cell growth.
Abstract: The cyclin-dependent kinase 4 (CDK4) regulates progression through the G1 phase of the cell cycle. The activity of CDK4 is controlled by the opposing effects of the D-type cyclin, an activating subunit, and p16INK4, an inhibitory subunit. Ectopic expression of p16INK4 blocked entry into S phase of the cell cycle induced by oncogenic Ha-Ras, and this block was relieved by coexpression of a catalytically inactive CDK4 mutant. Expression of p16INK4 suppressed cellular transformation of primary rat embryo fibroblasts by oncogenic Ha-Ras and Myc, but not by Ha-Ras and E1a. Together, these observations provide direct evidence that p16INK4 can inhibit cell growth.

Journal ArticleDOI
TL;DR: It is demonstrated that adenovirus-mediated over-expression of human p21 inhibits growth factor-stimulated VSMC proliferation in vitro by efficiently arresting VSMCs in the G1 phase of the cell cycle, and suggested a novel cytostatic gene therapy approach for restenosis and related vascular proliferative disorders.
Abstract: Vascular smooth muscle cell (VSMC) proliferation after arterial injury is important in the pathogenesis of a number of vascular proliferative disorders, including atherosclerosis and restenosis after balloon angioplasty. Thus, a better understanding of the molecular mechanisms underlying VSMC proliferation in response to arterial injury would have important therapeutic implications for patients with atherosclerotic vascular disease. The p21 protein is a negative regulator of mammalian cell cycle progression that functions both by inhibiting cyclin dependent kinases (CDKs) required for the initiation of S phase, and by binding to and inhibiting the DNA polymerase delta co-factor, proliferating cell nuclear antigen (PCNA). In this report, we show that adenovirus-mediated over-expression of human p21 inhibits growth factor-stimulated VSMC proliferation in vitro by efficiently arresting VSMCs in the G1 phase of the cell cycle. This p21-associated cell cycle arrest is associated both with significant inhibition of the phosphorylation of the retinoblastoma gene product (Rb) and with the formation of complexes between p21 and PCNA in VSMCs. In addition, we demonstrate that localized arterial infection with a p21-encoding adenovirus at the time of balloon angioplasty significantly reduced neointimal hyperplasia in the rat carotid artery model of restenosis. Taken together, these studies demonstrate the important role of p21 in regulating Rb phosphorylation and cell cycle progression in VSMC, and suggest a novel cytostatic gene therapy approach for restenosis and related vascular proliferative disorders.

Journal ArticleDOI
TL;DR: The morphology of cells undergoing apoptosis is similar to cells undergoing both normal mitosis and an aberrant form of mitosis called mitotic catastrophe, suggesting that the underlying biochemical changes also may be related.
Abstract: Programmed cell death, or apoptosis, is a highly regulated process used to eliminate unwanted or damaged cells from multicellular organisms. The morphology of cells undergoing apoptosis is similar to cells undergoing both normal mitosis and an aberrant form of mitosis called mitotic catastrophe. During each of these processes, cells release substrate attachments, lose cell volume, condense their chromatin, and disassemble the nuclear lamina. The morphological similarities among cells undergoing these processes suggest that the underlying biochemical changes also may be related. The susceptibility of cells to apoptosis frequently depends on the differentiation state of the cell. Additionally, cell cycle checkpoints appear to link the cell cycle to apoptosis. Deregulation of the cell cycle components has been shown to induce mitotic catastrophe and also may be involved in triggering apoptosis. Some apoptotic cells express abnormal levels of cell cycle proteins and often contain active Cdc2, the primary kinase active during mitosis. Although cell cycle components may not be involved in all forms of apoptosis, in many instances cell proliferation and cell death may share common pathways.

Journal ArticleDOI
TL;DR: The secondary hyperparathyroidism of 5/6 nephrectomized rats was characterized by an increase in PTH mRNA levels and PT cell proliferation which were both markedly decreased by a low phosphate diet, and the number of PCNA positive cells was increased by a high phosphate diet.
Abstract: Secondary hyperparathyroidism is characterized by an increase in parathyroid (PT) cell number, and parathyroid hormone (PTH) synthesis and secretion. It is still unknown as to what stimuli regulate PT cell proliferation and how they do this. We have studied rats with dietary-induced secondary hyper- and hypoparathyroidism, rats given 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and rats after 5/6 nephrectomy for the presence of PT cell proliferation and apoptosis. PT cell proliferation has been measured by staining for proliferating cell nuclear antigen (PCNA) and apoptosis by in situ detection of nuclear DNA fragmentation and correlated with serum biochemistry and PTH mRNA levels. A low calcium diet led to increased levels of PTH mRNA and a 10-fold increase in PT cell proliferation. A low phosphate diet led to decreased levels of PTH mRNA and the complete absence of PT cell proliferation. 1,25 (OH)2D3 (25 pmol/d x 3) led to a decrease in PTH mRNA levels and unlike the hypophosphatemic rats there was no decrease in cell proliferation. There were no cells undergoing apoptosis in any of the experimental conditions. The secondary hyperparathyroidism of 5/6 nephrectomized rats was characterized by an increase in PTH mRNA levels and PT cell proliferation which were both markedly decreased by a low phosphate diet. The number of PCNA positive cells was increased by a high phosphate diet. Therefore hypocalcemia, hyperphosphatemia and uremia lead to PT cell proliferation, and hypophosphatemia completely abolishes this effect. Injected 1,25 (OH)2D3 had no effect. These findings emphasize the importance of a normal phosphate and calcium in the prevention of PT cell hyperplasia.

Journal ArticleDOI
TL;DR: Glycosphingolipids, cell type-specific markers which change dramatically during ontogenesis and oncogenesis, have been implicated as playing major roles in cellular interactions and control of cell proliferation in multicellular organisms.
Abstract: Glycosphingolipids (GSLs), cell type-specific markers which change dramatically during ontogenesis and oncogenesis, have been implicated as playing major roles in cellular interactions and control of cell proliferation in multicellular organisms. These functional roles have been partially clarified through two types of studies: (i) Studies of cell recognition mediated by (a) GSL-GSL interaction, (b) GSL-lectin interaction, and (c) GSL-dependent modulation of integrin receptor function. (ii) Studies on control of transmembrane signaling by GSLs and/or sphingosine (Sph) derivatives, with emphasis on effects of these compounds on: (a) signaling pathways initiated by tyrosine kinase-linked receptors; (b) signaling systems mediated by protein kinase C, MAP kinase, other kinases, or cytosolic Ca2+ concentration, leading to changes in cellular phenotypes such as motility, proliferation, differentiation, and apoptosis.