title: Downregulation of ERK2 is essential for the inhibition of radiation-induced cell death in HSP25 overexpressed L929 cells.
abstract: We previously reported that overexpression of HSP25 delayed cell growth, increased the level of p21(waf), reduced the levels of cyclin D1, cyclin A and cdc2, and induced radioresistance in L929 cells. In this study, we demonstrated that HSP25 induced-radioresistance was abolished by transfection with plasmids containing antisense hsp25 cDNA. Extracellular regulated kinase (ERK) and MAP kinase/ERK kinase (MEK) expressions as well as their activation (phospho-forms) were inhibited by hsp25 overexpression. Furthermore, when control vector transfected cells were treated with PD98059, MEK inhibitor, they became resistant to radiation, suggesting that inhibition of ERK1/2 activities was essential for radioresistance in L929 cells. To confirm the relationship between ERK1/2 and hsp25-mediated radioresistance, ERK1 or ERK2 cDNA was transiently transfected into the hsp25 overexpressed cells and their radioresistance was examined. HSP25-mediated radioresistance was abolished by overexpression of ERK2, but not by overexpression of ERK1. Alteration of cell cycle distribution and cell cycle related protein expressions (cyclin D, cyclin A and cdc2) by hsp25 overexpression were also recovered by ERK2 cDNA transfection. Increase in Bcl-2 protein by hsp25 gene transfection was also reduced by subsequent ERK2 cDNA-transfection. Taken together, these results suggest that downregulation of ERK2 is essential for the inhibition of radiation-induced cell death in HSP25 overexpressed cells.
authors.affiliation: Laboratory of Radiation Effect, Korea Cancer Center Hospital, 215-4 Gongneung-Dong, Nowon-Ku, Seoul 139-706, Korea.
authors.forename: H N
authors.initials: HN
authors.lastname: Cho
authors.forename: Y J
authors.initials: YJ
authors.lastname: Lee
authors.forename: C K
authors.initials: CK
authors.lastname: Cho
authors.forename: S J
authors.initials: SJ
authors.lastname: Lee
authors.forename: Y-S
authors.initials: YS
authors.lastname: Lee
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D002460:Cell Line; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression; D006360:Heat-Shock Proteins; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011836:Radiation Tolerance; D014162:Transfection
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D006360:Heat-Shock Proteins; C486113:Hsbp1 protein, mouse; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one