Rapid tyrosine phosphorylation of an 85,000 M(r) protein after phorbol ester stimulation of EL4 thymoma cells.
Early signalling events between protein kinase C (PKC) activation and lymphokine transcription were compared between phorbol ester-sensitive and -resistant EL4 cell lines which do or do not respond with interleukin 2 (IL2) production, respectively. The earliest event detected in the sensitive cell line was a dramatic increase in the tyrosine phosphorylation of an 85,000 M(r) protein (p85; 30 s), followed by mobility shifts of raf-1, mitogen-activated protein kinase kinase (MEK), mitogen-activated protein (MAP) kinase, lck and ZAP-70 (within 5 min). In contrast, p85 was not detected in the resistant cell line and lck and raf-1 mobility shifts exhibited delayed kinetics. Both vanadate and okadaic acid blocked the phorbol ester-stimulated p85 tyrosine phosphorylation in the sensitive cell line, suggesting that a phosphatase activity downstream of PKC activation may be required for p85 tyrosine phosphorylation. Characterization of p85 and its regulation should help elucidate some of the earliest events in this PKC pathway.
Richardson
A F
AF
Department of Pharmacology, University of Virginia, Charlottesville 22908, USA.
Sando
J J
JJ
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D015151:Immunoblotting; D008213:Lymphocyte Activation; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D048728:MAP Kinase Kinase Kinase 1; D051379:Mice; D008970:Molecular Weight; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects*; D014443:Tyrosine / Q000378:metabolism*; D051746:ZAP-70 Protein-Tyrosine Kinase
D011518:Proto-Oncogene Proteins; D015240:Phorbol 12,13-Dibutyrate; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; C497262:Zap70 protein, mouse; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482578:Map3k1 protein, mouse