Signal transduction through the T cell antigen receptor. Activation of phospholipase C through a G protein-independent coupling mechanism.
The T cell Ag (Ti-CD3) receptor complex has been proposed to regulate phosphoinositide-specific phospholipase C (PLC) through a cholera toxin (CTX)-sensitive guanine nucleotide-binding (G) protein. In this study, we have used CTX and staurosporine as pharmacologic probes to further define the linkage between the Ti-CD3 receptor and PLC activity in the human T cell line, Jurkat. CTX pretreatment inhibited Ti-CD3 receptor-dependent phosphoinositide hydrolysis and, concomitantly, protein tyrosine kinase activation in intact cells. Studies with electrically permeabilized Jurkat cells revealed that guanosine 5'-(3-O-thio) triphosphate stimulated an increase in PLC activity, that unlike the response to Ti-CD3 receptor ligation, was not affected by cellular pretreatment with CTX. In contrast, the phosphotyrosine phosphatase inhibitors, orthovanadate and molybdate anions, stimulated phosphoinositide hydrolysis in permeabilized cells through a CTX-sensitive mechanism of PLC activation. Additional studies with a known PTK inhibitor, staurosporine, supported the results obtained with CTX. Staurosporine pretreatment inhibited the phosphoinositide hydrolysis induced by anti-CD3 antibodies or phosphotyrosine phosphatase inhibitors, but failed to alter the G protein-dependent PLC activation response to guanosine 5'-(3-O-thio) triphosphate. The results of this study indicate that PLC activity(s) in Jurkat cells are regulated by both G protein- and PTK-dependent coupling mechanisms. However, the differential inhibitory effects of CTX and staurosporine on these PLC activation pathways strongly suggest that a protein tyrosine kinase activation event, rather than a G protein, mediates the functional linkage between the Ti-CD3 receptor and PLC activity in Jurkat cells.
Augustine
J A
JA
Department of Immunology, Mayo Clinic, Rochester, MN 55905.
Secrist
J P
JP
Daniels
J K
JK
Leibson
P J
PJ
Abraham
R T
RT
D000470:Alkaloids / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002772:Cholera Toxin / Q000494:pharmacology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D010716:Phosphatidylinositols / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D015398:Signal Transduction; D019311:Staurosporine; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000502:physiology*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D000470:Alkaloids; D010716:Phosphatidylinositols; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; D019000:Phosphotyrosine; D014443:Tyrosine; D002772:Cholera Toxin; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D019311:Staurosporine; D002118:Calcium