Browsing by Subject "Hepatoma"
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Item Open Access Lithium-mediated downregulation of PKB/Akt and cyclin E with growth inhibition in hepatocellular carcinoma cells(Wiley-Liss, Inc, 2005) Erdal, E.; Ozturk, N.; Cagatay, T.; Eksioglu-Demiralp, E.; Ozturk, M.We studied in vitro effects of glycogen synthase kinase 3β (GSK3β)-inhibitor lithium on the growth of hepatocellular carcinoma (HCC) cells. Lithium induced strong growth inhibition (>70%) in 75% (n = 9 of 12) of cell lines, apparently independent from the status of major genes that are mutated in HCC including p53, p16INK4a, β-catenin and Axin1. Comparative studies with a growth-sensitive Huh7 and growth-resistant Hep40 cell lines showed that lithium induces growth arrest in Huh7 cells but not in Hep40 cells. Lithium induced the accumulation of N-terminally phosphorylated inactive form of GSK3β with concomitant increase in β-catenin and β-catenin/TCF transcriptional activity in both cell lines. This suggests that lithium-mediated HCC growth inhibition is independent of its well-known stimulatory effect on Wnt-β-catenin signaling. The main differences between Huh7 and Hep40 responses to lithium treatment were observed at the levels PKB/Akt and cyclin E proteins. Lithium induced depletion of both proteins in growth-sensitive Huh7, but not in growth-resistant Hep40 cells. PKB/Akt and Cyclin E are 2 major proteins that are known to be constitutively active in HCC. The targeting of both proteins with lithium may be the main reason why most HCC cells are responsive to lithium-mediated growth inhibition, independent of their p53, retinoblastoma and Wnt-β-catenin pathways. The exploration of molecular mechanisms involved in lithium-mediated growth inhibition in relation with PKB/Akt and cyclin E downregulation may provide new insights for therapy of liver tumors. © 2005 Wiley-Liss, Inc.Item Open Access p53 but not p16(INK4a) induces growth arrest in retinoblastoma-deficient hepatocellular carcinoma cells(Elsevier, 2000-08) Morel, A. P.; Unsal, K.; Cagatay, T.; Ponchel, F.; Carr, B.; Ozturk, M.Background/Aim: Both p16(INK4a) and p53 proteins are negative regulators of the cell cycle. In human hepatocellular carcinomas (HCC), the loss of function of p53, retinoblastoma (pRb) and p16(INK4a) genes by different mechanisms has been largely documented, but their hepatocellular effects are poorly known. We compared the growth-inhibitory effects of p16(INK4a)and p53 proteins in Hep3B cell line-derived clones. Methods: Cells were transfected with inducible p16(INK4a) and p53 expression vectors, and stable clones were analyzed for transgene expression by Western blotting and immunoperoxidase staining. Effects on cell growth were analyzed by in vitro growth assay, thymidine incorporation and flow cytometry. Biochemical effects of p53 were tested by Northern blotting of p21(Cip1) transcripts and by Western blotting of p21(Cip1) mdm-2, bax, cyclin-dependent kinase 2 and cyclin E proteins. The pRb protein was studied by Western blotting and immnunoprecipitation assays. Results: The induction of p16(INK4a) protein expression did not affect in vitro growth of cells. In contrast, p53 protein in its wild-type conformation provoked a growth arrest accompanied by transactivation of p21(Cip1) gene and accumulation of p21(Cip1), bax and mdm-2 proteins, p53-induced growth arrest was due to a cell cycle arrest at the GI/S transition, probably mediated by p21(Cip1) protein, which inhibits cyclin-dependent kinase 2/cyclin E complexes. Conclusions: The lack of detectable pRb protein and resistance of cells to p16(INK4a) strongly suggest that p53 is able to arrest the growth of HCC cells by a mechanism independent of 'p53-retinoblastoma pathway'. These findings are applicable to HCC with abberrations of both p53 and pRb genes, and may not represent the universal effects of p53 in hepatic cells.