Protein kinase C (PKC) activation via human leucocyte antigen class II molecules. A novel regulation of PKC activity.

Analysis of intracellular localization of protein kinase C (PKC) in a lymphoblastoid B cell line shows that anti-human leucocyte antigen (HLA) class II antibodies induce an increase of cytosolic and membrane PKC activities. This phenomenon is both time- and dose-dependent. The maximal PKC activation was observed after exposure to 12.5 micrograms/ml antibody for 30 to 45 min. Unlike TPA, no translocation of the cytosolic PKC was observed at any time following exposure to the anti-HLA class II antibodies. We observed a good correlation between the [3H]phorbol dibutyrate binding activity and the enzymatic activity of PKC. Using a panel of antibodies specific for the HLA class II isotypes (DP, DQ, DR), we demonstrated that PKC activation via HLA class II molecules is not restricted to one isotype. We also showed by Western blot analysis that the increased PKC activity correlates with a quantitative increase of PKC. The increase of PKC activity induced by anti-HLA class II antibodies was completely abolished by the treatment with actinomycin D, a transcriptional inhibitor, or cycloheximide, a translational inhibitor. Finally, Northern blot analysis revealed that anti-HLA class II antibodies induce an increase of the PKC alpha and PKC beta mRNAs levels which are significant after 20 min of stimulation and rose to a maximum after 60 min. In summary, our results show that increased PKC activity induced by HLA class II antibody is regulated at the transcriptional level.