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 the translocation of inactive cytosolic enzyme to the lipid environment of membranes. However, by using a novel method for measuring PKC activity directly in isolated membranes, we have previously shown that a significant proportion of the PKC present in a variety of cells associates with membranes in an inactive state, and that this pool of inactive PKC can be stimulated specifically in cells in the absence of translocation. IL-2 did not stimulate the translocation of PKC to membranes in the IL-2-dependent mouse T cell line, CTLL-2. Nevertheless, a transient, two approximately threefold increase in membrane PKC activity was observed within 10 min of IL-2 addition to these cells. This increase was entirely caused by the activation of a pool of inactive membrane PKC previously associated with the membrane. The inhibition of PKC activity by the specific inhibitors bisindolylmaleimide (BIS) and 1-O-hexadecyl-2-O-methyl-rac-glycerol (AMG) blocked the ability of IL-2 to suppress the onset of apoptosis in IL-2 and serum-deprived CTLL-2 cells. The inhibition of this important function of IL-2 was most pronounced when the PKC inhibitors were added to the medium within 2 h of stimulating 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 suppresses cell death in T lymphocytes.