title: Conditional expression of mitogen-activated protein kinase phosphatase-1, MKP-1, is cytoprotective against UV-induced apoptosis.
abstract: UV irradiation induces apoptosis in U937 human leukemic cells that is accompanied by the activation of both the stress-activated protein kinase (SAPK) and p38 mitogen-activated protein kinase (MAPK) signal transduction pathways. The MAPK phosphatase, MKP-1, is capable of inactivating both SAPK and p38 MAPK in vivo. To determine whether MKP-1-mediated inhibition of SAPK and/or p38 MAPK activity provided cytoprotection against UV-induced apoptosis, a U937 cell line conditionally expressing MKP-1 from the human metallothionein IIa promoter was established. Conditional expression of MKP-1 was found to abolish UV-induced SAPK and p38 MAPK activity, and inhibit UV-induced apoptosis as judged by both morphological criteria and DNA fragmentation. MKP-1 was also found to inhibit other biochemical events associated with apoptosis, including activation of caspase-3 and the proteolytic cleavage of the caspase-3 substrate, poly(ADP ribose) polymerase. These findings demonstrate that MKP-1 acts at a site upstream of caspase activation within the apoptotic program. The cytoprotective properties of MKP-1 do not appear to be mediated by its ability to inhibit p38 MAPK because the p38 MAPK specific inhibitor SB203580 had no effect on UV-induced apoptosis in U937 cells. Furthermore, by titrating the level of MKP-1 expression it was found that MKP-1 inhibited UV-induced SAPK activity, DNA fragmentation, and caspase-3 activation in a similar dose-dependent manner. The dual-specificity phosphatase, PAC1, which does not inhibit UV-induced activation of SAPK, did not provide a similar cytoprotection against UV-induced apoptosis. These results are consistent with a model whereby MKP-1 provides cytoprotection against UV-induced apoptosis by inhibiting UV-induced SAPK activity.
authors.affiliation: Department of Medicine, Division of Medical Oncology, University of Colorado Health Sciences Center, Denver, CO 80262, USA. cfrankli@u.washington.edu
authors.forename: C C
authors.initials: CC
authors.lastname: Franklin
authors.forename: S
authors.initials: S
authors.lastname: Srikanth
authors.forename: A S
authors.initials: AS
authors.lastname: Kraft
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D018797:Cell Cycle Proteins; D054638:Dual Specificity Phosphatase 1; D054641:Dual Specificity Phosphatase 2; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D011494:Protein Kinases / Q000378:metabolism; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D011836:Radiation Tolerance / Q000502:physiology*; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D018797:Cell Cycle Proteins; D017874:Immediate-Early Proteins; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; C517019:DUSP1 protein, human; C517032:DUSP2 protein, human; D054638:Dual Specificity Phosphatase 1; D054641:Dual Specificity Phosphatase 2; D017027:Protein Tyrosine Phosphatases