GROWTH OF MELANOCYTIC CELLS IS ASSOCIATED WITH DOWN-REGULATION OF PROTEIN-KINASE-C ALPHA-ISOFORM, DELTA-ISOFORM, AND EPSILON-ISOFORM - POSSIBLE ROLE OF DIACYLGLYCEROL

Citation
G. Brooks et al., GROWTH OF MELANOCYTIC CELLS IS ASSOCIATED WITH DOWN-REGULATION OF PROTEIN-KINASE-C ALPHA-ISOFORM, DELTA-ISOFORM, AND EPSILON-ISOFORM - POSSIBLE ROLE OF DIACYLGLYCEROL, The Journal of biological chemistry, 268(32), 1993, pp. 23868-23875
Citations number
28
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
268
Issue
32
Year of publication
1993
Pages
23868 - 23875
Database
ISI
SICI code
0021-9258(1993)268:32<23868:GOMCIA>2.0.ZU;2-7
Abstract
Protein kinase C (PKC) down-regulation has been shown to correlate wit h the growth of murine melanocytic cells in culture (Brooks, G., Wilso n, R. E., Dooley, T. P., Goss, M. W., and Hart, I. R. (1991) Cancer Re s. 51, 3281-3288). We now show that PKC alpha, delta, epsilon, and zet a isoforms are present at the protein level in quiescent, non-transfor med Mel-ab melanocytes, maintained in the absence of phorbol ester. Pr oliferation of Mel-ab cells, achieved by incubation in the continual p resence of phorbol 12,13-dibutyrate, was associated with a down-regula tion of the PKC alpha, delta, and epsilon isozymes. Examination of two transformed syngeneic lines (the B16 murine melanoma and the long ter minal repeat Ras.2 line), that grew in the absence of exogenous phorbo l esters, showed that PKC alpha protein levels were either partially d own-regulated or unaffected, the PKC delta and epsilon isoforms were d own-regulated completely, and the levels of PKC zeta protein remained unaltered relative to quiescent Mel-ab cells. Basal levels of total di acylglycerol were elevated 5-fold in B16 melanoma cells compared with levels found in quiescent or proliferating Mel-ab melanocytes and appe ar to arise largely from the breakdown of phosphatidylinositol phospho lipids accompanied by a significant rise in phospholipase C activity. Hourly treatments of quiescent Mel-ab melanocytes with the synthetic d iacylglycerol analogue, 1,2-dioctanoyl-sn-glycerol, for 24 h, resulted in an induction of DNA synthesis which was associated with a signific ant down-regulation of PKC levels mediated largely via post-translatio nal rather than transcriptional mechanisms. These results show for the first time that specific isoforms of PKC are down-regulated at the pr otein level during proliferation of murine melanocytic cells and sugge st that the constitutive down-regulation of PKC in transformed melanom a cells may arise as a consequence of elevated endogenous phosphatidyl inositol-derived diacylglycerol levels.