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

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 PP2C gamma promotes spliceosome assembly. We show that PP2C gamma's distinctive acidic domain is essential for its activity in splicing and interacts with YB-1, a spliceosome-associated factor. Moreover, PP2C gamma is a phosphoprotein in vivo, and its acidic domain is phosphorylated under splicing conditions in vitro. PP2C gamma phosphorylation enhances its interaction with YB-1 and is reversed by the phosphatase in cis. PP2Cc 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 PP2C gamma's acidic domain, which is essential to promote inclusion of CD44 exons v4 and v5 in vivo. We propose that PP2C gamma modulates alternative splicing of specific pre- mRNAs coregulated by YB-1.