title: HSP70 deficiency results in activation of c-Jun N-terminal Kinase, extracellular signal-regulated kinase, and caspase-3 in hyperosmolarity-induced apoptosis.
abstract: In this study we examined the function of heat shock protein 70 (HSP70) in the hyperosmolarity-induced apoptotic pathway using hsp70.1-/-mouse embryonic fibroblasts (MEFs). When the cells were exposed to hyperosmotic stress, an absence of HSP70 negatively affected cell viability. Caspase-9 and caspase-3 were rapidly activated, and extensive cleavage occurred in focal adhesion and cytoskeletal molecules in the hsp70.1-/-MEFs. In contrast, hsp70.1+/+ MEFs exhibited no caspase-9 or caspase-3 activation and finally recovered intact cell morphology when cells were shifted back to an isosmotic state. Because HSP70 might be involved in the regulation of mitogen-activated protein kinase (MAPK) activities with regard to various cellular activities, we also monitored MAPK phosphorylation. The absence of HSP70 affected c-Jun N-terminal kinase phosphorylation. However, it had no effect on p38. Sustained phosphorylation of extracellular signal-regulated kinase (ERK) was observed during the hyperosmolarity-induced apoptosis of hsp70.1-/-MEFs. Inhibition of ERK activity by the treatment of PD98059 accelerated the apoptotic pathway. ERK phosphorylation was precisely correlated with shift of mitogen-activated protein kinase phosphatase-3 from the soluble to insoluble fraction. Our results demonstrate that the inhibitory effect of HSP70 on caspase-3 activation is sufficient to inhibit apoptosis and that HSP70 exhibits regulatory functions to c-Jun N-terminal kinase and ERK phosphorylation in hyperosmolarity-induced apoptosis.
authors.affiliation: ILCHUN Molecular Medicine Institute, Medical Research Center and Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine and BK21 Human Life Science, Seoul National University, Seoul, Korea. jeongsun@snu.ac.be
authors.forename: Jae-Seon
authors.initials: JS
authors.lastname: Lee
authors.forename: Je-Jung
authors.initials: JJ
authors.lastname: Lee
authors.forename: Jeong-Sun
authors.initials: JS
authors.lastname: Seo
mesh_terms: D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D054638:Dual Specificity Phosphatase 1; D004622:Embryo, Mammalian / Q000166:cytology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009997:Osmotic Pressure; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D014162:Transfection
chemical_list: D061945:Caspase Inhibitors; D018840:HSP70 Heat-Shock Proteins; C081884:heat-shock protein 70.1; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; C517020:Dusp1 protein, mouse; D017027:Protein Tyrosine Phosphatases; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases