Broad specificity in binding of NIPP-1, nuclear inhibitor of protein phosphatase-1, to PP1 isoforms in vivo

Protein phosphatase type-1 (PP1), one of the most abundant Ser/Thr protein phosphatases, plays a central role in the regulation of various cell functi ons. Almost all the PP1 molecules exist as holoenzymes in vivo consisting o f a catalytic subunit (PP1C) and a variable regulatory subunit that regulat es substrate specificity and/or subcellular localization. In order to clari fy fine regulation of PP1, we overexpressed a nuclear inhibitor of PP1 (NIP P-1) in a Flag-tagged form in mammalian cells. The Flag-tagged NIPP-1 was f ound to be immunoprecipitated with three isoforms of PP1C, namely, PP1 alph a, PP1 gamma 1, and PP1 sigma with a similar efficiency, suggesting that NI PP-1 makes a complex with the PP1C through the region conserved among the t hree isoforms. These results suggested that NIPP-1 can be involved in the r egulation of various PP1 holoenzymes in vivo. (C) 2000 Tohoku University Me dical Press.