Protein phosphatase X interacts with c-Rel and stimulates c-Rel/nuclear factor kappa B activity

Nuclear factor kappa B (NF-kappa B) and the Rel family of proteins are plei otropic transcription factors that play central roles in the immune and inf lammatory responses, as well as apoptosis. Here, we identified a serine/thr eonine protein phosphatase X (PPX; also called protein phosphatase 4 (PP4)) that specifically associated with c-Rel, NF-kappa B p50, and RelA. The ami no acid sequences of human and mouse PPX are 100% identical, and the PPX ge ne was mapped to human chromosome 16 p11.2. Overexpression of PPX, but not catalytically inactive PPX mutants, stimulated the DNA-binding activity of c-Rel and activated NF-kappa B-mediated transcription These results suggest that PPX is a novel activator of c-Rel/NF-kappa B.