FAM122A, a new endogenous inhibitor of protein phosphatase 2A.

The regulation of the ubiquitously expressed protein phosphatase 2A (PP2A) is essential for various cellular functions such as cell proliferation, transformation, and fate determination. In this study, we demonstrate that the highly conserved protein in mammals, designated FAM122A, directly interacts with PP2A-Aa and B55a rather than B56a subunits, and inhibits the phosphatase activity of PP2A-Aa/B55a/Ca complex. Further, FAM122A potentiates the degradation of catalytic subunit PP2A-Ca with the increased poly-ubiquitination. In agreement, FAM122A silencing inhibits while its overexpression enhances cell growth and colony- forming ability. Collectively, we identify FAM122A as a new endogenous PP2A inhibitor and its physiological and pathophysiological significances warrant to be further investigated.