title: Phosphorylation of protein kinase Cdelta on distinct tyrosine residues induces sustained activation of Erk1/2 via down-regulation of MKP-1: role in the apoptotic effect of etoposide.
abstract: The mechanism underlying the important role of protein kinase Cdelta (PKCdelta) in the apoptotic effect of etoposide in glioma cells is incompletely understood. Here, we examined the role of PKCdelta in the activation of Erk1/2 by etoposide. We found that etoposide induced persistent activation of Erk1/2 and nuclear translocation of phospho-Erk1/2. MEK1 inhibitors decreased the apoptotic effect of etoposide, whereas inhibitors of p38 and JNK did not. The activation of Erk1/2 by etoposide was downstream of PKCdelta since the phosphorylation of Erk1/2 was inhibited by a PKCdelta-KD mutant and PKCdelta small interfering RNA. We recently reported that phosphorylation of PKCdelta on tyrosines 64 and 187 was essential for the apoptotic effect of etoposide. Using PKCdeltatyrosine mutants, we found that the phosphorylation of PKCdeltaon these tyrosine residues, but not on tyrosine 155, was also essential for the activation of Erk1/2 by etoposide. In contrast, nuclear translocation of PKCdelta was independent of its tyrosine phosphorylation and not necessary for the phosphorylation of Erk1/2. Etoposide induced down-regulation of kinase phosphatase-1 (MKP-1), which correlated with persistent phosphorylation of Erk1/2 and was dependent on the tyrosine phosphorylation of PKCdelta. Moreover, silencing of MKP-1 increased the phosphorylation of Erk1/2 and the apoptotic effect of etoposide. Etoposide induced polyubiquitylation and degradation of MKP-1 that was dependent on PKCdelta and on its tyrosine phosphorylation. These results indicate that distinct phosphorylation of PKCdeltaon tyrosines 64 and 187 specifically activates the Erk1/2 pathway by the down-regulation of MKP-1, resulting in the persistent phosphorylation of Erk1/2 and cell apoptosis.
authors.affiliation: William and Karen Davidson Laboratory of Cell Signaling and Tumorigenesis, Hermelin Brain Tumor Center, Department of Neurosurgery, Henry Ford Hospital, Detroit, Michigan 48202, USA.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Lomonaco
authors.forename: Sarit
authors.initials: S
authors.lastname: Kahana
authors.forename: Michal
authors.initials: M
authors.lastname: Blass
authors.forename: Yehuda
authors.initials: Y
authors.lastname: Brody
authors.forename: Hana
authors.initials: H
authors.lastname: Okhrimenko
authors.forename: Cunli
authors.initials: C
authors.lastname: Xiang
authors.forename: Susan
authors.initials: S
authors.lastname: Finniss
authors.forename: Peter M
authors.initials: PM
authors.lastname: Blumberg
authors.forename: Hae-Kyung
authors.initials: HK
authors.lastname: Lee
authors.forename: Chaya
authors.initials: C
authors.lastname: Brodie
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis; D054638:Dual Specificity Phosphatase 1 / Q000378:metabolism*; D005047:Etoposide / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D018613:Microscopy, Confocal; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010766:Phosphorylation; D051745:Protein Kinase C-delta / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D014443:Tyrosine; D005047:Etoposide; D051745:Protein Kinase C-delta; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1