Alternative splicing regulation by interaction of phosphatase PP2Cγ with nucleic acid–binding protein YB-1

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Abstract
Kinases and phosphatases participate in precursor messenger RNA (pre-mRNA) splicing regulation, but their precise roles and the identities of their cofactors and substrates remain poorly understood. The human Ser/Thr phosphatase PP2Cγ promotes spliceosome assembly. We show that PP2Cγ's distinctive acidic domain is essential for its activity in splicing and interacts with YB-1, a spliceosome-associated factor. Moreover, PP2Cγ is a phosphoprotein in vivo, and its acidic domain is phosphorylated under splicing conditions in vitro. PP2Cγ phosphorylation enhances its interaction with YB-1 and is reversed by the phosphatase in cis. PP2Cγ knockdown leaves constitutive splicing unaffected but inhibits cell proliferation and affects alternative splicing of CD44, a YB-1 target. This effect on splicing regulation is mediated by PP2Cγ's acidic domain, which is essential to promote inclusion of CD44 exons v4 and v5 in vivo. We propose that PP2Cγ modulates alternative splicing of specific pre-mRNAs coregulated by YB-1.