Multiple pathways for the regulation of p21ras in T lymphocytes

Abstract

T lymphocyte activation via the antigen receptor complex (TCR) and CD2 antigen results accumulation of p21ras in the active GTP bound state. Stimulation of protein kinase (PKC) can also activate p21ras and we have proposed a model that the TCR regulating p21ras occurs as a consequence of TCR regulation of PKC. The T cell growth factor Interleukin-2 (IL-2) does not activate PKC in T cells and yet IL-2 can induce p21ras activation. These data imply that both PKC and non PKC mediated pathways for activation of p21ras exist in T cells. To test the role of PKC in TCR regulation of p21 ras we have used a permeabilized cell system to examine TCR regulation of p21ras under conditions where TCR activation of PKC is blocked i.e. 1)use of a PKC pseudosubstrate inhibitor, 2)use of ionic conditions (OnM Ca2+ in the permeabilisation buffer) that block diacylglycerol production by phospholipase C. TCR stimulation of p21ras was much less sensitive to PKC pseudosubstrate inhibition comparing to that exerted by PDBu. On the other hand, when PLC-induced PKC activation was blocked the stimulation of the TCR was still able to activate p21ras. The results obtained suggest that there are two main pathways for TCR regulation of p21ras in T cells, one involving PKC activation and one that does not.