ABSTRACT
The pleckstrin homology (PH) domain is a protein module of approximately 100 amino acids, that has been found in signaling molecules, including serinelthreonine kinase, GTPase-activating protein, phospholipase, and some cytoskeletal proteins. Although the specific function of PH domain has not been defined yet, it is believed that this domain is involved in the regulation of signal transduction pathway. The expression plasmids of human PLCg PH domains were constructed to see the roles of them in IL-6 signal transduction. When these expression plasmids are transfected into B9 cells, only N-terminal of PH domain inhibited IL-6-induced B9 cell proliferation. These results suggest that N-terminal of PH domain is critical for IL-6 signal transduction in B9 cells. To search the binding proteins associated PH domains of PLCy1 in B9 cells, Glutathione S-trnaferase (GST) fusion proteins containg PH domains were expressed in E. coli. Then, IL-6-dependent B9 cells were treated with 10 unit/ml IL-6 and the cell lysates were immunoprecipited with GST-PH doman fusion proteins. In vitro kinase assay of immune complex demonstrated that p38 (38 KDa) protein was coprecipitated with NC fusion protein, but IL-6 had no additional effect on it. When S-methaionine labelled cell lysates were used for immunoprecipitation, the same result was observed, conforming the association of p38 with NC motive of PH domain.