Phosphorylation at a tyrosine residue of lipomodulin in mitogen-stimulated murine thymocytes.
When murine thymocytes were stimulated by mitogens such as concanavalin A, the Ca2+ ionophore A23187, or 4 beta-phorbol 12-myristate 13-acetate, there was a marked increase of 32P incorporation into immunoprecipitable lipomodulin, a phospholipase inhibitory protein. These compounds enhanced 45Ca2+ influx into thymocytes, which, in turn, increased protein phosphorylation, probably by Ca2+- and phospholipid-dependent protein kinase (protein kinase C). Cyclic 8-bromo-AMP, an inhibitor of lymphocyte mitogenesis, blocked the mitogen-stimulated phosphorylation of lipomodulin, although it stimulated the protein phosphorylation via cyclic AMP-dependent kinase (protein kinase A). On electrophoresis, the hydrolysates of 32P-labeled lipomodulin showed a single radioactive spot, which comigrated with authentic phosphotyrosine. The partially purified middle-sized tumor antigen was able to phosphorylate lipomodulin after being phosphorylated by protein kinase C but not by the catalytic subunit of protein kinase A. Our findings suggest that the activity of a tyrosine-specific kinase, which phosphorylates lipomodulin in vivo as well as in vitro, is stimulated by protein kinase C and inhibited by protein kinase A.
D000818:Animals; D017302:Annexins; D002135:Calcium-Binding Proteins; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology; D006023:Glycoproteins; D008213:Lymphocyte Activation; D051379:Mice; D008938:Mitosis; D010750:Phosphoproteins / Q000378:metabolism*; D019000:Phosphotyrosine; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D013950:Thymus Gland / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism
D017302:Annexins; D002135:Calcium-Binding Proteins; D006023:Glycoproteins; D010750:Phosphoproteins; D011506:Proteins; C030958:lipomodulin; D019000:Phosphotyrosine; D014443:Tyrosine; D000242:Cyclic AMP; D011494:Protein Kinases; D011493:Protein Kinase C