title: Role of constitutively activated and insulin-like growth factor-stimulated ERK1/2 signaling in human hepatoma cell proliferation and apoptosis: evidence for heterogeneity of tumor cell lines.
abstract: Enhanced insulin-like growth factor II (IGF-II) and type I IGF receptor (IGF-IR) gene expression in liver tumors and the development of liver tumors in transgenic mice overexpressing IGF-II in the liver suggest that the IGFs and underlying signaling cascades may play auto/paracrine roles in the control of hepatocarcinoma (HCC) cell proliferation and in their protection against apoptosis. We have focused on the role of mitogen-activated protein kinase (ERK1/2) signaling on human HepG2 and Huh-7 hepatoma cell proliferation and on the protection of these cells against drug-induced apoptosis. Physiological concentrations of IGF-I stimulated DNA replication in HepG2 cells (1.5-fold) but not in Huh-7 cells, and this effect was abolished by PD98059 (MEK-1 inhibitor). Doxorubicin or cisplatin treatment induced apoptosis (caspase-dependent poly[ADP-ribose]polymerase cleavage) in both cell lines, but dose-dependent reversion of drug-induced apoptosis (57-84%) by IGF-I was only observed in HepG2 cells. The very low level of IGF-IR at the plasma membrane of Huh-7 cells may account for their unresponsiveness to IGF-I. We have shown that drug treatment enhanced (17-fold) or did not modify constitutive ERK1/2 activity in cultured HepG2 or Huh-7 cells, respectively. In both cell lines, inhibition of constitutive and drug-induced ERK1/2 activity by PD98059 yielded a complete inhibition of drug-induced apoptosis. Altogether, our data demonstrate the heterogeneous response of human hepatoma cells to an IGF stimulus and suggest (1) that auto/paracrine effects of IGF-I/-II might contribute to the proliferation of HCC cells and to their protection against apoptosis in vivo and (2) that drug-induced activation of ERK1/2 plays a role in drug-induced apoptosis in human hepatoma cells.
authors.affiliation: Institut National de la Sané et de la Recherche Médicale U481, Faculté de Médecine Xavier Bichat, 16 rue Henri Huchard, BP 416, 75870 Paris Cédex 18, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Alexia
authors.forename: Malika
authors.initials: M
authors.lastname: Lasfer
authors.forename: André
authors.initials: A
authors.lastname: Groyer
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000473:pathology*; D002455:Cell Division; D045744:Cell Line, Tumor; D004261:DNA Replication / Q000187:drug effects; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D008113:Liver Neoplasms / Q000201:enzymology / Q000473:pathology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D020928:Mitogen-Activated Protein Kinases