The role of protein kinase C in IL-2 signal transduction.
Creators: name: Lu, Yin.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1996
Subjects: subject: Biology, Molecular.

description: Interleukin 2 (IL-2), one of the most important lymphokines secreted by activated helper T-cells, plays a pivotal role in the generation and regulation of the immune response. The role of protein kinase C (PKC) in the signal transduction of IL-2 and the mechanisms of PKC activation were investigated in the cytotoxic T-cell line, CTLL-2. IL-2 is critical for CTLL-2 cell survival and cytolytic activity. CTLL-2 cells possess measurable levels of PKC activity and this activity was responsive to IL-2 withdrawal and addition. The IL-2 stimulated PKC activation was not due to the PKC translocation from cytosol to the membrane, but rather from the activation of inactive PKC already resident on membranes. Secondly, IL-2's ability to maintain cell viability was dependent on PKC activity since specific PKC inhibitors were able to block IL-2's ability to suppress apoptosis. An early and transient PKC activation was needed for IL-2 induced suppression of apoptosis. Finally, the mechanism(s) responsible for the IL-2 induced activation of PKC in CTLL-2 cells was investigated. While tyrosine kinases were activated after IL-2 stimulation, they were probably not linked to the activation of PKC. On the other hand, a pertussis toxin sensitive-G-protein was likely involved in PKC activation since pertussis toxin blocked IL-2 stimulated PKC activation. DAG, but not IP$\sb3$ and intracellular calcium, increased after IL-2 stimulation, indicated that DAG was unlikely generated from the breakdown of PI, but more likely via the PC-PLC or PC-PLD pathways. The increase in DAG by IL-2 was likely responsible for the PKC activation since exogenously applied DAG stimulated PKC activation in both intact cells and in isolated membranes. IL-2 also stimulated the levels of AA in CTLL-2 cells. This increase likely resulted from increased PLA$\sb2$ activity since PLA$\sb2$ inhibitors effectively blocked the IL-2 stimulated activation of PKC. As was the case with DAG, the addition of exogenous AA to intact cells and to isolated membranes caused a rapid increase in membrane PKC activity, suggesting that the endogenous production of AA by IL-2R stimulation was likely linked to PKC activation in CTLL-2 cells. The possible involvement of a cytoplasmic factor in IL-2 stimulated PKC activation was investigated. This compound, designated factor X, is likely a protein(s) with a molecular weight of less than 10 kDa. Factor X was rapidly generated following IL-2 stimulation of CTLL-2 cells, and the cytosolic fraction isolated from IL-2 treated, but not control cells, potently stimulated PKC activity in isolated membranes. Its role in the pathway leading to PKC activation after IL-2R stimulation is unclear, although it appears not to act upstream or to be linked to the G-protein or the generation of AA and DAG. In summary, IL-2 stimulated PKC in CTLL-2 cells, not through the translocation of cytosolic enzyme to membrane, but via activation of inactive membrane associated PKC. This PKC activation was involved in IL-2's ability to suppress apoptosis in these cells. The mechanism(s) of PKC activation by IL-2 is substantially more complicated than we initially thought, and it likely involved multiple second messengers, including G-proteins, DAG, AA and factor X. (Abstract shortened by UMI.)