βII Protein Kinase C Is Required for the G2/M Phase Transition of Cell Cycle

doi:10.1074/jbc.271.25.15045

β_II Protein Kinase C Is Required for the G₂/M Phase Transition of Cell Cycle*

From the Sealy Center for Oncology and Hematology, University of Texas Medical Branch, Galveston, Texas 77555

^‡ Leukemia Society of America Scholar. To whom correspondence should be addressed:
Sealy Center for Oncology and Hematology, University of Texas Medical Branch, Medical Research Bldg., Rm. 9.104, 301 University Blvd., Galveston, TX 77555-1048.
Tel.: 409-747-1940; Fax: 409-747-1938 E-mail: afields{at}beach.utmb.edu

Abstract

Entry into mitosis requires the coordinated action of multiple mitotic protein kinases. In this report, we investigate the involvement of protein kinase C in the control of mitosis in human cells. Treatment of synchronized HL60 cells with the highly selective protein kinase C (PKC) inhibitor chelerythrine chloride leads to profound cell cycle arrest in G₂ phase. The cellular effects of chelerythrine are not due to either direct or indirect inhibition of the known mitotic regulator p34^cdc2/cyclin B kinase. Rather, several lines of evidence demonstrate that chelerythrine-mediated G₂ phase arrest results from selective inhibition and degradation of β_II protein kinase C. First, chelerythrine causes dose-dependent inhibition of β_II PKC in vitro with an IC₅₀ identical to that for G₂ phase blockade in whole cells. Second, chelerythrine specifically inhibits β_II PKC-mediated lamin B phosphorylation and mitotic nuclear lamina disassembly. Third, chelerythrine leads to selective loss of β_II PKC during G₂ phase in synchronized cells. Fourth, chelerythrine mediates activation-dependent degradation of PKC, indicating that β_II PKC is selectively activated during G₂ phase of cell cycle. Taken together, these data demonstrate that β_II PKC activation at G₂ phase is required for mitotic nuclear lamina disassembly and entry into mitosis and that β_II PKC-mediated phosphorylation of nuclear lamin B is important in these events.

Footnotes

↵* This work was supported in part by National Institutes of Health Grants GM43186 and CA56869 (to A. P. F.). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

PKC

protein kinase C

PBS

phosphate-buffered saline

BSA

bovine serum albumin

DAPI

4′,6-diamidino-2-phenylindole

PAGE

polyacrylamide gel electrophoresis

diC₈

dioctanoylglycerol.
↵² L. J. Thompson and A. P. Fields, unpublished results
- Received December 20, 1995.
- Revision received March 21, 1996.