The proteolysis of membrane-associated protein kinase C as a possible component of the signalling pathway leading to c-myc induction in B lymphocytes.
Occupancy of surface immunoglobulin (sIg) receptor for antigen expressed on resting B cells initiates increased turnover of membrane-associated phosphatidylinositol (PI), which ultimately leads to the enhanced expression of c-myc mRNA. The mechanism which links these initial membrane biochemical changes to subsequent alterations in c-myc transcription is unclear. The present study examines the possible involvement of PKC and its calpain-generated proteolytic fragment, protein kinase M (PKM), in conveying the membrane-associated signal to the nucleus. Utilizing an in vitro phosphorylation assay, we have shown that a calcium-dependent protease, similar to calpain, is involved in the downregulation of membrane-associated PKC induced by anti-immunoglobulin or phorbol 12-myristate 13-acetate (PMA) and ionomycin stimulation of resting B cells. In addition, we have confirmed previous studies showing that PMA and ionomycin are both required for optimal expression of c-myc mRNA. The enhanced expression of c-myc mRNA is sensitive to inhibitors of PKC, such as H-7 and sangavimycin, providing evidence for a prominent role of PKC and/or PKM in the receptor-mediated up-regulation of c-myc message expression. Finally, a calpain inhibitor interferes with the transmission of the membrane-associated signal which induces the increased expression of c-myc mRNA. Our results are consistent with the hypothesis that the calpain-mediated proteolysis of membrane-associated PKC is involved in the sIg-mediated signal transduction pathway.
Pollok
K E
KE
Department of Microbiology and Immunology, University of Kentucky Medical Center, Lexington 40536-0084.
Snow
E C
EC
D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000378:metabolism*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology*; D002478:Cells, Cultured; D004789:Enzyme Activation; D005260:Female; D005786:Gene Expression Regulation; D016259:Genes, myc; D006868:Hydrolysis; D007700:Kinetics; D051379:Mice; D008811:Mice, Inbred DBA; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015290:Second Messenger Systems
D012333:RNA, Messenger; D011493:Protein Kinase C; D002118:Calcium