Activation of PKCα Downstream from Caspases during Apoptosis Induced by 7-Hydroxystaurosporine or the Topoisomerase Inhibitors, Camptothecin and Etoposide, in Human Myeloid Leukemia HL60 Cells

• Published in: The Journal of biological chemistry 1997-12, Vol.272 (50), p.31321
• Main Authors: Rong-Guang Shao, Chun-Xia Cao, Yves Pommier
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.50.31321

We previously demonstrated that the anticancer agent and protein kinase C (PKC) inhibitor 7-hydroxystaurosporine (UCN-01) induces apoptosis independently of p53 and protein synthesis in HL60 cells. We now report the associated changes of PKC isoforms. PKCα, βI, βII, δ, and ζ activities were measured after immunoprecipitation of cytosols from UCN-01-treated HL60 cells. UCN-01 had no effect on PKCζ and inhibited kinase activity of PKCβI, βII, and δ. PKCα activity was initially inhibited at 1 h, and subsequently increased as cells underwent apoptosis 3 h after the beginning of UCN-01 treatment. Camptothecin (CPT) and etoposide (VP-16) also markedly enhanced PKCα activity during apoptosis in HL60 cells. However, CPT did not affect PKCβI, βII and ζ, and activated PKCδ. PKCα activation was not due to increased protein levels or proteolytic cleavage but was associated with PKCα autophosphorylation in vitro and increased phosphorylation in vivo . We also found that not only PKC δ but also PKC βI was proteolytically activated in HL60 cells during apoptosis. The PKCα activation and hyperphosphorylation were abrogated by N -benzyloxycarbonyl-Val-Ala-Asp( O -methyl)-fluoromethylketone (z-VAD-fmk) under conditions that abrogated apoptosis. z-VAD-fmk also prevented PKCδ and βI proteolytic activation. Together these findings suggest that caspases regulate PKC activity during apoptosis in HL60 cells. At least two modes of activation were observed: hyperphosphorylation for PKCα and proteolytic activation for PKC δ and βI.