Mitogenic response of murine B lymphocytes to Salmonella typhimurium lipopolysaccharide requires protein kinase C-dependent late tyrosine phosphorylations.
Unlike the cross-linking of membrane immunoglobulins, the activation of B cells by lipopolysaccharide (LPS) does not involve the phosphoinositol turnover and the initial activation of tyrosine kinases. However, LPS-induced B-cell proliferation was inhibited by the tyrosine kinase inhibitors genistein and herbimycin A even when added 48 h after the beginning of the culture. Tyrosyl-phosphorylated proteins were detected by Western blotting after 24 h of culture with LPS, reaching a maximum concentration after 72 h. Late tyrosine phosphorylations were also detected in B cells activated for 72 h with anti-immunoglobulin M antibody and were abrogated by the protein synthesis inhibitor cycloheximide, the tyrosine kinase inhibitors genistein and herbimycin A, and the protein kinase C inhibitor chelerythrine. The role of protein kinase C in late tyrosine kinase activation is independent of Ca2+ mobilization and was confirmed by detection of a comparable but restricted pattern of tyrosine-phosphorylated substrates in B cells treated with phorbol myristate acetate alone or in association with ionomycin. Tyrosine kinase activation was dependent on de novo protein synthesis. However, culture supernatants of LPS-activated B cells were devoid of mitogenic activity and induced a phosphorylation pattern more restricted than that achieved by LPS. Altogether these data indicate that proliferation signals induced by LPS or by the cross-linking of membrane immunoglobulins are controlled by late tyrosine phosphorylations occurring throughout the first 3 days of culture, controlled in part by protein kinase C activation, and dependent on the synthesis of an intermediate protein(s) either not secreted in the culture supernatant or present but biologically inactive in naive B cells.
Mey
A
A
Immunology Laboratory, INSERM U80, Hopital E. Herriot, Lyon, France.
Revillard
J P
JP
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D003513:Cycloheximide / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000276:immunology*; D008213:Lymphocyte Activation; D051379:Mice; D008934:Mitogens / Q000276:immunology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012486:Salmonella typhimurium / Q000276:immunology*; D015398:Signal Transduction; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism
D008070:Lipopolysaccharides; D008934:Mitogens; D011500:Protein Synthesis Inhibitors; D014443:Tyrosine; D003513:Cycloheximide; D011493:Protein Kinase C