A protein kinase C-activating phorbol ester accelerates the T cell antigen receptor-stimulated phosphatidylinositol cycle in normal human CD4+ T cells.
Ligation of the TCR on Jurkat T lymphoblastoid cells causes an 1,4,5-inositol trisphosphate-dependent rise in intracellular cytoplasmic calcium that is inhibited by PMA, a potent activator of protein kinase C. Consequently, protein kinase C is widely believed to mediate feedback inhibition of TCR-activated phospholipase C. We have now extended these studies to normal unblasted human CD4+ T lymphocytes, examining the PMA sensitivity of both the TCR complex-mediated release of total inositol-phosphates and the resynthesis of the parent phosphoinositides. In contrast to Jurkat, in which PMA inhibited release of 1,4,5-inositol trisphosphate by 60% and total inositolphosphates by 40% (50% inhibitory concentration, 5.6 nM), normal cells displayed a marked increase in anti-CD3-induced phosphatidylinositol (PI) cycling in the presence of PMA. Both total inositolphosphate release and PI resynthesis were maximally elevated (88% and 342%, respectively) by a PMA concentration that also optimally supported a subsequent proliferative response; the ED50 was at least 11.7-fold lower than that for the inhibitory effect of PMA on breakdown of total Jurkat PI. A PKC nonactivating phorbol ester had no effect. If anti-CD3 was replaced by the mitogenic lectin PHA, PI resynthesis was similarly up-regulated by PMA in these highly purified cells. The PMA up-regulatory phenomenon was not a simple consequence of cell blastogenesis, inasmuch as there was no early effect on the non-signaling-associated phosphatidylethanolamine compartment after CD3 stimulation. Thus, PKC activation appears to accelerate TCR-linked PI metabolism in normal Th cells, in contrast to the feedback inhibitor paradigm observed in Jurkat and other tumor cell systems.
Whelan
J P
JP
Department of Microbiology/Immunology, Baylor College of Medicine, Houston, TX 77030.
Shearer
W T
WT
Gilliam
E B
EB
Hardy
K J
KJ
D000945:Antigens, Differentiation, T-Lymphocyte / Q000502:physiology; D017252:CD3 Complex; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D010716:Phosphatidylinositols / Q000096:biosynthesis / Q000378:metabolism*; D010835:Phytohemagglutinins; D011493:Protein Kinase C / Q000502:physiology*; D011948:Receptors, Antigen, T-Cell / Q000187:drug effects* / Q000502:physiology*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D010716:Phosphatidylinositols; D010835:Phytohemagglutinins; D011948:Receptors, Antigen, T-Cell; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate