Showing papers on "PI3K/AKT/mTOR pathway published in 1992"

Adiponectin inhibits colorectal cancer cell growth through the AMPK/mTOR pathway.

Abstract: Adiponectin is a peptide hormone secreted by adipose tissue. It is a key hormone responsible for insulin sensitization, and its circulating level is inversely associated with abdominal obesity. Recent studies have shown that a reduced plasma adiponectin level is significantly correlated with the risk of various cancers. However, there are few studies regarding the association of adiponectin and colorectal cancer. To address this issue, we investigated the effect of adiponectin on colorectal cancer cells. Three colorectal cancer cell lines express both AdipoR1 and AdipoR2 receptors. MTT assay revealed that adiponectin inhibited human colorectal cancer cell growth. Furthermore, Western blot analysis revealed that adiponectin activated adenosine monophosphate-activated protein kinase (AMPK) and suppressed mammalian target of rapamycin (mTOR) pathways. Selective AMPK inhibitor compound C abrogated the inhibitory effect of adiponectin on cell growth. Our results clearly demonstrate the novel findings that adiponectin inhibits colorectal cancer cell growth via activation of AMPK, thereby down-regulating the mTOR pathway.

Inhibition of Stearoyl-CoA Desaturase 1 expression in human lung adenocarcinoma cells impairs tumorigenesis.

Abstract: Saturated (SFA) and monounsaturated (MUFA) fatty acids, the most abundant fatty acid species, have many divergent biological effects including the regulation of cell proliferation, programmed cell death and lipid-mediated cytotoxicity. Their distribution is regulated by Stearoyl-CoA Desaturases (SCD), the enzymes that convert SFA into MUFA. A positive correlation between high levels of tissue MUFA and several types of cancer has been reported, but a causal relationship between the function of SCD1, the main human SCD isoform, and cancer development has not yet been firmly established. Here we report that the stable knockdown of SCD1 gene expression in A549 human lung adenocarcinoma cells decreased the ratio MUFA/SFA in total lipids and inhibited the incorporation of glucose into cell lipids. Cell proliferation and anchorage-independent growth were considerably decreased in SCD1-depleted cells, whereas the rate of apoptosis was elevated, with respect to control A549 cells. In addition, phosphorylation of Akt-Ser473 and GSK-3beta-Ser9 was found notably impaired in SCD1-ablated A549 cells. Interestingly, the effects of SCD1 blockade on Akt activation, cancer cell growth and apoptosis could not be reversed by exogenously added oleic acid. Remarkably, the reduction of SCD1 expression in lung cancer cells significantly delayed the formation of tumors and reduced the growth rate of tumor xenografts in mice. Our study demonstrates that SCD1 activity regulates Akt activation and determines the rate of cell proliferation, survival and invasiveness in A549 cancer cells and shows, for the first time, that SCD1 is a key factor in the regulation of tumorigenesis in vivo.

Targeted therapy of human osteosarcoma with 17AAG or rapamycin: characterization of induced apoptosis and inhibition of mTOR and Akt/MAPK/Wnt pathways.

Abstract: Osteosarcoma is highly resistant to current chemotherapy regimens. Novel therapeutic approaches, potentially involving targeting of specific survival pathways, are needed. We used 17-AAG to inhibit Hsp90 and rapamycin to inhibit mTOR, in the osteosarcoma cell lines, HOS and KHOS/NP. HOS and KHOS cells were treated for 24 and 48 h with 17-AAG or rapamycin and studied drug-induced apoptosis, cell cycle, mitochondrial membrane potential and levels of reduced glutathione (GSH), dephosphorylation of signal transduction proteins in the Akt/MAP kinase pathway and mTOR signaling. 17-AAG was a potent inducer of apoptosis, involving effective depletion of GSH and mitochondrial membrane (MM) depolarization, strong activation of caspase-8 and -9 and release of AIF from mitochondria to the cytosol. Furthermore, 17-AAG down-regulated pAkt, p44Erk, p-mTOR, p70S6, TSC1/2 and pGSK-3beta. Treatment with 17-AAG also caused down-regulation of cyclin D1, GADD45a, GADD34 and pCdc2 and upregulation of cyclin B1 and mitotic block. A decrease in Hsp90 and increase in Hsp70 and Hsp70 C-terminal fragments were also observed. Rapamycin was a less potent inducer of apoptosis, involving a small decrease in GSH and MM potential with no activation of caspases or release of AIF. Rapamycin strongly inhibited cell growth with an increase in G1 and a decrease in S-phase of the cell cycle concomitant with down-regulation of cyclin D1. Rapamycin also down-regulated the activity of p70S6, pAkt and p-mTOR, but had no effect on pGSK-3beta, p44Erk, pCdc2, TSC1/2 or Hsp70 or Hsp90. We conclude that Hsp90 inhibition merits further study in the therapy of osteosarcoma.

Advanced glycation end product (AGE)-induced proliferation of HEL cells via receptor for AGE-related signal pathways.

Abstract: This study investigated whether advanced glycation end products (AGE) and RAGE (receptor for AGE) are involved in the proliferation of leukemia cells. AGE strongly induced the proliferation of primary acute myeloid leukemia (AML) cells and cell lines. MAP kinase, PI3K and JAK/STAT pathways were involved in cellular proliferation of HEL cells by AGE. RAGE antisense S-ODN effectively inhibited cell growth, induced apoptosis and reversed AGE-induced expression of targeting molecules in HEL cells. The study demonstrated for the first time that AGE directly induced human AML cell proliferation via the MAPK, PI3K and JAK/STAT pathways.

Estrogen and progestin regulate metastasis through the PI3K/AKT pathway in human ovarian cancer

Abstract: Estrogen and progestin are involved in ovarian carcinogenesis. Change in nm23-H1 expression and the PIK3/AKT pathway are involved in carcinogenesis, development, invasion and metastasis of ovarian cancers. Therefore, it is critical to understand the signaling pathways that regulate hormone-induced cell migration and invasion in ovarian cancer. We investigated nm23-H1, AKT and pAKT expression by using immunohistochemical staining in ovarian clear cell adenocarcinoma, ovarian benign, borderline and malignant serous tumors and analyzed their relationship with prognostic factors. Using ES-2 and SKOV-3 ovarian cancer cell lines, we studied the modulation of estrogen and progestin on cell migration and invasion as well as their effect on AKT, pAKT and nm23-H1 expression. Furthermore, the signaling pathways were examined using pharmacological inhibitors (LY294002 and PD98059) or AKT siRNA combined with estrogen or progestin in the two cell lines. Weak nm23-H1 and high AKT and pAKT expression was observed in ovarian serous adeno-carcinoma and ovarian clear cell adenocarcinoma. Our data demonstrated that the expression of nm23-H1 was negatively correlated with tumor stage and grade and lymph node metastasis, whereas the expression of AKT/pAKT was positively correlated with these clinic factors. Estrogen up-regulated pAKT expression and reduced nm23-H1 expression, which ultimately resulted in increased cell migration and invasion. In contrast, progestin reduced pAKT expression and increased nm23-H1 expression, which inhibited cell migration. PIK3 kinase inhibitor LY294002 antagonized the effect of estrogen. On the other hand, it reinforced the effect of progestin. Our data suggest that AKT and pAKT are unfavorable prognostic factors for ovarian serous adenocarcinoma and clear cell carcinomas whereas nm23-H1 expression predicates favorable patient prognosis. Estrogen down-regulates nm23-H1 expression and promotes cell migration and invasion by activating the PIK3/AKT pathway. Progestin has an opposing effect.

SHIP2 phosphoinositol phosphatase positively regulates EGFR-Akt pathway, CXCR4 expression, and cell migration in MDA-MB-231 breast cancer cells.

Abstract: The phosphoinositol phosphatase SHIP2 is an important regulator of energy metabolism. SHIP2 dephosphorylates phosphatidylinositol 3,4,5 trisphosphates which are critical second messengers in signaling pathways induced by various extracellular stimuli including insulin. SHIP2 also regulates cytoskeleton remodeling, cell adhesion and spreading. In addition, endogenous SHIP2 in HeLa cells regulates receptor endocytosis and ligand-induced EGFR degradation. Further, SHIP2 in MDA-MB-231 breast cancer cells regulates EGFR levels and supports in vitro cell proliferation and in vivo tumor growth and spontaneous metastasis. Here we examine the role of SHIP2 in EGF signaling in breast cancer cells using RNA interference. Our results show that suppression of SHIP2 in MDA-MB-231 breast cancer cells alters EGF and EGFR internalization. Upon SHIP2 silencing, EGF-induced Akt activation was reduced causing decreased nuclear levels of activated Akt. Cytokine receptor CXCR4, a downstream element of EGFR-Akt pathway that plays an important role in metastasis, is down-regulated upon SHIP2 knockdown. Finally, cell adhesion and EGF-induced cell migration were suppressed in SHIP2 silenced cells. These results demonstrate a positive role of SHIP2 in EGF-induced Akt activation, CXCR4 expression, and cell migration in breast cancer cells.

Over-expression of ubiquitin carboxy terminal hydrolase-L1 induces apoptosis in breast cancer cells.

Abstract: Ubiquitin carboxy terminal hydrolase-L1 (UCH-L1) belongs to the UCH proteases family that deubiquitinates ubiquitin-protein conjugates in the ubiquitin-proteasome system. Previous research showed that UCH-L1 was expressed in mouse retinal cells and testicular germ cells, and its function was associated with apoptosis. But it is still unclear whether UCH-L1 is concerned with apoptosis in tumor cells. In order to clarify the role of UCH-L1 in tumor cells, multi-drug resistance (MDR) human breast carcinoma cell line MCF7/Adr, that expresses relatively high UCH-L1, and its parental cell line MCF7, that expresses relatively low UCH-L1, were chosen for this study. We transfected pcDNA3.1-UCH-L1 plasmid and UCH-L1 siRNA into MCF7 and MCF7/Adr cells, respectively. Using 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, western blot, Hoechst 33258 staining assay and flow cytometry, we found that over-expression of UCH-L1 in MCF7 cells induced apoptosis. On the other hand, silencing of UCH-L1 in MCF7/Adr cells led to the opposite effect. Moreover, to explore the mechanism underling these observations, we further investigated the expression of phospho-Akt and its downstream signal phospho-IkB-alpha and other signal molecules including Fas, Fas-L, Trail, DR4, DR5, Bax, cytochrome C, active caspase-3, phospho-p53, phospho-Mdm-2, Bcl-2, Bcl-xL, p21 and p27. The results indicated that the process of apoptosis triggered by UCH-L1 is, at least in part, probably through Phosphoinositide 3-kinase (PI3K)/Akt signal pathway. Our findings suggest that modulating the ubiquitination and deubiquitination pathway could be a novel method for tumor therapy.

uPA/uPAR downregulation inhibits radiation-induced migration, invasion and angiogenesis in IOMM-Lee meningioma cells and decreases tumor growth in vivo.

Abstract: Meningioma is a well-known tumor of the central nervous system, and is treated by surgical resection and/or radiation. Recently, ionizing radiation has been shown to enhance invasiveness of surviving tumor cells, and several proteolytic enzyme molecules, including urokinase plasminogen activator (uPA), seem to be upregulated after radiation. uPA and its receptor (uPAR) have been strongly implicated in tumor invasion, angiogenesis and progression. Hence, the tumor-associated uPA-uPAR system is considered a potential target for cancer therapy. In the present study, we show that radiation increases uPA levels in the IOMM-Lee meningioma cells, and subsequently, increases tumor invasion, migration and angiogenesis in vitro. Studies with signaling molecule inhibitors AG1478, U0126 and SB203580 (specific inhibitors of EGFR, MEK1/2 and p38 respectively) showed inhibition of uPA levels in both basal and irradiated-IOMM-Lee cells. The PI3K inhibitor (LY294002) and the AKT inhibitor (AKT inhibitor IV) also partially decreased uPA expression, whereas SP600125, a JNK inhibitor, did not affect uPA levels in either radiated or non-radiated cells. Further, a bicistronic plasmid construct with small interfering RNA (siRNA) against uPA and its receptor inhibited tumor invasion, migration and angiogenesis in radiation-treated IOMM-Lee cells. In addition, siRNA against uPA and its receptor inhibited subcutaneous tumor growth in athymic nude mice in combination with radiation in a synergistic manner. Thus, the specific targeting of proteases via RNA interference could augment the therapeutic effect of radiation and prevent the adverse effects resulting from tumor cells that receive sublethal doses of radiation within the tumor mass.

Sphingosine-1-phosphate inhibits the cytotoxic activity of NK cells via Gs protein-mediated signalling.

Abstract: Sphingosine-1-phosphate (S1P) is a bioactive phospholipid that transmits signals through G-protein-coupled receptors to control cellular differentiation, survival, and several functions of immune cells. S1P is a chemoattractant for NK cells, which are critical members of the immunological tumor surveillance machinery. In this study we analyzed the influence of S1P on the interaction of NK cells with tumor cells such as the human melanoma cell line Hs294T and the Burkitt's lymphoma cell line Raji. We found that S1P inhibited the cytotoxic activity of NK cells. Analysis of signal transduction pathways revealed that S1P induced common signalling pathways of chemotaxins such as Gi protein-dependent actin reorganization and activation of the phosphatidylinositol 3-kinase (PI3K) dependent signal molecules, protein kinase B (PKB/Akt) and glycogen synthase kinase-3beta (GSK-3beta). In contrast to most chemotaxins, S1P is also able to activate Gs-dependent signalling molecules. This signalling cascade involves increase of cAMP levels and protein kinase A (PKA) activation. Additionally, blocking the regulatory subunits of PKA I abrogated the inhibitory effect of S1P, whereas the catalytic subunits were not involved. Our data indicate that S1P may contributes to the tumor escape from NK cell-dependent immunological surveillance machinery.