14-3-3ζ regulates nuclear trafficking of protein phosphatase 1α (PP1α) in HEK-293 cells

Protein phosphatase 1 (PP1) is one of the major Ser/Thr phosphatases in mammalian cells. There are four isoforms of PP1 namely, PP1 alpha, PP1 beta/delta, PP1 gamma(1) and PP1 gamma(2). PP1 gamma and PP1 beta translocate to the nucleus by binding to a co-transporter that contains a nuclear localization signal. The mechanism by which PP1 alpha shuttles between the nucleus and the cytosol is not known. In this study, we found that PP1 alpha co-immunoprecipitates with 14-3-3 zeta; from HEK-293 cell lysates. By co-immunoprecipitation and GST pull-down assay, we determined that 14-3-3 zeta; binds to both PP1 alpha (WT) and PP1 alpha (T320A), and that phosphorylation of PP1 alpha is not required for binding. Using PP1 alpha deletion mutants, we located the 14-3-3 zeta; binding region within PP1 alpha residues 159-279. An in vitro assay showed that 14-3-3 zeta; does not affect PP1 alpha activity. When HEK-293 cells expressing PP1 alpha and 14-3-3 zeta; were subjected to subcellular fractionation, the ratio of cytosolic vs. nuclear PP1 alpha was significantly higher in cells expressing PP1 alpha and 14-3-3 zeta; than those expressing PP1 alpha alone. In cells expressing a dominant negative 14-3-3 zeta; (K49E), PP1 alpha accumulated in the nucleus. Our results show that 14-3-3 zeta; binds to PP1 alpha and causes its retention in the cytosol which suggests that 14-3-3 zeta; regulates nuclear trafficking of PPla in mammalian cells. (C) 2014 Elsevier Inc. All rights reserved.