title: MAPK signaling in cisplatin-induced death: predominant role of ERK1 over ERK2 in human hepatocellular carcinoma cells.
abstract: Hepatocellular carcinoma treatment by arterial infusion of cis-diamminedichloroplatinum-II (cisplatin) exhibits certain therapeutic efficacy. However, optimizations are required and the mechanisms underlying cisplatin proapoptotic effect remain unclear. The mitogen-activated protein kinase (MAPK) pathway plays a key role in cell response to cisplatin and the functional specificity of the isoform MAPK/ERK kinase 1 and 2 (MEK1/2) and ERK1/2 could influence this response. The individual contribution of each kinase on cisplatin-induced death was thus analyzed after a transient or stable specific inhibition by RNA interference in the human hepatocellular carcinoma cells Huh-7 or in knockout mice. We demonstrated here that ERK1 played a predominant role over ERK2 in cisplatin-induced death, whereas MEK1 and MEK2 acted in a redundant manner. Indeed, at clinically relevant concentrations of cisplatin, ERK1 silencing alone was sufficient to protect cells from cisplatin-induced death both in vitro, in Huh-7 cells and ERK1(-/-) hepatocytes, and in vivo, in ERK1-deficient mice. Moreover, we showed that ERK1 activity correlated with the induction level of the proapoptotic BH3-only protein Noxa, a critical mediator of cisplatin toxicity. On the contrary, ERK2 inhibition upregulated ERK1 activity, favored Noxa induction and sensitized hepatocarcinoma cells to cisplatin. Our results point to a crucial role of ERK1 in cisplatin-induced proapoptotic signal and lead us to propose that ERK2-specific targeting could improve the efficacy of cisplatin therapy by increasing ERK1 prodeath functions.
authors.affiliation: Inserm U1085, Institut de Recherche sur la Santé l'Environnement et le Travail IRSET, Université de Rennes 1, Biosit,  F-35043 Rennes, France.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Guégan
authors.forename: Frédéric
authors.initials: F
authors.lastname: Ezan
authors.forename: Nathalie
authors.initials: N
authors.lastname: Théret
authors.forename: Sophie
authors.initials: S
authors.lastname: Langouët
authors.forename: Georges
authors.initials: G
authors.lastname: Baffet
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D016923:Cell Death / Q000187:drug effects*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D006801:Humans; D008113:Liver Neoplasms / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D020935:MAP Kinase Signaling System; D051379:Mice; D018345:Mice, Knockout
chemical_list: D000970:Antineoplastic Agents; D002945:Cisplatin