Repo-Man recruits PP1γ to chromatin and is essential for cell viability

Abstract

Protein phosphatase 1 (PP1) is a ubiquitous serine/threonine phosphatase regulating many cellular processes. PP1α and -γ are closely related isoforms with distinct localization patterns, shown here by time-lapse microscopy of stably expressed fluorescent protein fusions. A pool of PP1γ is selectively loaded onto chromatin at anaphase. Using stable isotope labeling and proteomics, we identified a novel PP1 binding protein, Repo-Man, which selectively recruits PP1γ onto mitotic chromatin at anaphase and into the following interphase. This approach revealed both novel and known PP1 binding proteins, quantitating their relative distribution between PP1α and -γ in vivo. When overexpressed, Repo-Man can also recruit PP1α to chromatin. Mutating Repo-Man's PP1 binding domain does not disrupt chromatin binding but abolishes recruitment of PP1 onto chromatin. RNA interference–induced knockdown of Repo-Man caused large-scale cell death by apoptosis, as did overexpression of this dominant-negative mutant. The data indicate that Repo-Man forms an essential complex with PP1γ and is required for the recruitment of PP1 to chromatin.

Ki67 Antigen Contributes to the Timely Accumulation of Protein Phosphatase 1γ on Anaphase Chromosomes

“…We noticed that one region corresponding to residues 142-173 of human Ki67 (NP_001139438.1) contained a canonical PP1-binding motif, RVXF (33). We also noticed that Ki67 showed a significantly high similarity to Repo-MAN, a protein known to play a role in targeting PP1␥ to anaphase chromosomes (28), throughout the region (Fig. 1A).…”

“…We also sexamined the localization of YFP-PP1␥ in cells depleted of Repo-MAN (Fig. 2C), whose contribution to the event has been previously reported (28). Quantitative evaluation of the images illustrated that Ki67 does contribute to the accumulation of PP1␥ on anaphase chromosomes as Repo-MAN (Fig.…”

“…PP1␥ has many interaction partners, all of which are regulatory subunits important for targeting PP1␥ to diverse subcellular structures and for restricting its activity and/or specificity (27). In the context of targeting on anaphase chromosomes, a subset of PP1␥ is known to do this by forming a complex with Repo-MAN (28). The Repo-MAN⅐PP1␥ complex was shown to contribute to chromatin decondensation (29), although the relevant substrate to be dephosphorylated during the reaction has not been identified.…”

Modulation of Gene Expression and Cell-Cycle Signaling Pathways by the EGFR Inhibitor Gefitinib (Iressa) in Rat Urinary Bladder Cancer

“…Cdca2 is a cell-cycle regulator and selectively recruits PP1g onto mitotic chromatin at anaphase and into the subsequent interphase. Depletion of Cdca2 by RNAi knockdown leads to large-scale cell death by apoptosis, primarily in interphase; as did overexpression of this dominant-negative mutant (39). Cenpf is another cell-cycle regulator.…”

The Renaissance or the cuckoo clock

“…In animal cells, the PP1 phosphatase is recruited to a number of different sites at different times by distinct targeting subunits. For example, the RepoMan protein recruits PP1 to chromosomes in anaphase and this is important for chromosome decondensation [115]. Many more examples are likely to emerge in the near future as the role of phosphatases in cell cycle control continues its recent Renaissance.…”