p38 kinase mediates nitric oxide-induced apoptosis of chondrocytes through the inhibition of protein kinase C zeta by blocking autophosphorylation.

This study investigated the molecular mechanisms underlying inhibition of protein kinase C (PKC) zeta by p38 kinase during nitric oxide (NO)-induced apoptosis of chondrocytes. Coimmunoprecipitation experiments showed that activation of p38 kinase following addition of an NO donor resulted in a physical association between PKCzeta and p38 kinase. Direct interaction of p38 kinase with PKCzeta was confirmed in vitro using p38 kinase and PKCzeta recombinant proteins. p38 kinase interacts with the regulatory domain of PKCzeta and its association blocked PKCzeta autophosphorylation. Micro LC-MS/MS analysis using recombinant proteins indicated that the interaction of p38 kinase with PKCzeta blocked autophosphorylation of PKCzeta on Thr-560, which is required for PKCzeta activation. Collectively, our results demonstrate a novel mechanism of PKCzeta regulation: following activation by the production of NO, p38 kinase binds directly to the PKCzeta regulatory domain, preventing PKCzeta autophosphorylation on Thr-560, thereby inhibiting PKCzeta activation.