Translocation Inhibitors Define Specificity of Protein Kinase C Isoenzymes in Pancreatic β-Cells

doi:10.1074/jbc.272.3.1417

Translocation Inhibitors Define Specificity of Protein Kinase C Isoenzymes in Pancreatic β-Cells*

From the ^‡ Department of Endocrinology and Metabolism, Hebrew University-Hadassah Medical Center, 91120 Jerusalem, Israel and the
^§ Department of Molecular Pharmacology, Stanford University School of Medicine, Stanford, California 94035

^¶ To whom correspondence should be addressed:
Dept. of Endocrinology and Metabolism, Hadassah University Hospital, P.O. Box 12000, 91120 Jerusalem, Israel.
Tel.: 972-2-677-6787; Fax: 972-2-643-7940; E-mail: nesherr{at}cc.huji.ac.il

Abstract

The protein kinase C (PKC) family consists of 11 isoenzymes. Following activation, each isoenzyme translocates and binds to a specific eceptor for ctivated inase (RACK) (Mochly-Rosen, D. (1995) Science 268, 247-251) that provides an anchoring site in close proximity to the isoenzyme's specific substrate. Pancreatic islet cells contain at least six PKC isoenzymes (Knutson, K. L., and Hoenig, M. (1994) Endocrinology 135, 881-886). Although PKC activation enhances insulin release, the specific function of each isoenzyme is unknown. Here we show that following stimulation with glucose, αPKC and ϵPKC translocate to the cell's periphery, while δPKC and ζPKC translocate to perinuclear sites. βC2-4, a peptide derived from the RACK1-binding site in the C2 domain of βPKC, inhibits translocation of αPKC and reduces insulin response to glucose. Likewise, ϵV1-2, an ϵPKC-derived peptide containing the site for its specific RACK, inhibits translocation of ϵPKC and reduces insulin response to glucose. Inhibition of islet-glucose metabolism with mannoheptulose blocks translocation of both αPKC and ϵPKC and diminishes insulin response to glucose while calcium-free buffer inhibits translocation of αPKC but not ϵPKC and lowers insulin response by 50%. These findings illustrate the unique ability of specific translocation inhibitors to elucidate the isoenzyme-specific functions of PKC in complex signal transduction pathways.

Footnotes

↵* This work was supported in part by a grant from the JDF International (to R. N.) and from the Piccioto Foundation (to E. C.) and National Institutes of Health Grant HL43380 (to D. M.-R.). 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

KRB

Krebs Ringer bicarbonate

BSA

bovine serum albumin.
- Received May 29, 1996.
- Revision received November 1, 1996.