EVIDENCE THAT THE ACTIVATION OF AN INACTIVE POOL OF MEMBRANE-ASSOCIATED PROTEIN-KINASE-C IS LINKED TO THE IL-2-DEPENDENT SURVIVAL OF T-LYMPHOCYTES

The activation of protein kinase C (PKC) is believed to result from th e translocation of inactive cytosolic enzyme to the lipid environment of membranes. However, by using a novel method for measuring PKC activ ity directly in isolated membranes, we have previously shown that a si gnificant proportion of the PKC present in a variety of cells associat es with membranes in an inactive state, and that this pool of inactive PKC can be stimulated specifically in cells in the absence of translo cation. IL-2 did not stimulate the translocation of PKC to membranes i n the IL-2-dependent mouse T cell line, CTLL-2. Nevertheless, a transi ent, two similar to threefold increase in membrane PKC activity was ob served within 10 min of IL-2 addition to these cells. This increase wa s entirely caused by the activation of a pool of inactive membrane PKC previously associated with the membrane. The inhibition of PKC activi ty by the specific inhibitors bisindolylmaleimide (BIS) and 1-O-hexade cyl-2-O-methyl-rac-glycerol (AMG) blocked the ability of IL-2 to suppr ess the onset of apoptosis in IL-2 and serum-deprived CTLL-2 cells. Th e inhibition of this important function of IL-2 was most pronounced wh en the PKC inhibitors were added to the medium within 2 h of stimulati ng the cells with IL-2. The results suggest that transient activation of inactive membrane PKC is linked to the IL-2 receptor signaling, and may be an important step in the mechanism(s) by which the cytokine su ppresses cell death in T lymphocytes.