Selective redistribution of protein kinase C isozymes by thapsigargin and staurosporine.
Protein kinase C (PKC) is the major cellular receptor for tumor promoting phorbol esters. Phorbol esters activate alpha-, beta-, delta- and epsilon-PKCs in GH4C1 rat pituitary cells and cause their redistribution from a soluble to a particulate fraction. We have now characterized the effect of several non-phorbol ester tumor promoters on PKC isozyme distribution in GH4C1 cells. The incomplete tumor promoter mezerein caused redistribution of alpha-, beta-, delta- and epsilon-PKCs. Thus, it did not display partial agonist activity. The phosphatase inhibitor okadaic acid did not cause redistribution of any isozyme. The calcium ATPase inhibitor thapsigargin and the ser/thr kinase inhibitor staurosporine caused redistribution of epsilon-PKC and, to a lesser extent, delta-PKC. Although the mechanism of the selective effect on delta- and epsilon-PKCs is not yet known, these data clearly demonstrate that their subcellular distribution can be regulated by a pathway that does not influence alpha- and beta-PKCs. Phorbol ester activation of epsilon-PKC was associated with appearance of a more slowly migrating immunoreactive band in the particulate fraction. Both epsilon-PKC forms accumulated phosphate during phorbol ester treatment. The phosphorylated forms of epsilon-PKC were preferentially recovered in the particulate fraction. Although staurosporine caused redistribution, it prevented the phorbol dibutyrate (PDBu)-mediated appearance of the upper band of the doublet and the increased phosphorylation of both bands. The PDBu-mediated redistribution of alpha- and beta-PKCs was not inhibited by staurosporine, even though staurosporine effectively inhibited PKC catalytic activity. Therefore, catalytic activity is not required for redistribution.
Kiley
S C
SC
W. Alton Jones Cell Science Center, Inc., NY 12946-1099.
Parker
P J
PJ
Fabbro
D
D
Jaken
S
S
D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D007527:Isoenzymes / Q000187:drug effects*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010766:Phosphorylation; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000187:drug effects*; D051381:Rats; D019311:Staurosporine; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D000470:Alkaloids; D007527:Isoenzymes; D013729:Terpenes; D015240:Phorbol 12,13-Dibutyrate; D019284:Thapsigargin; D011493:Protein Kinase C; D019311:Staurosporine