title: Cell cycle-dependent phosphorylation of human CDC5 regulates RNA processing.
abstract: CDC5 proteins are components of the pre-mRNA splicing complex and essential for cell cycle progression in yeast, plants and mammals. Human CDC5 is phosphorylated in a mitogen-dependent manner, and its association with the spliceosome is ATP-dependent. Examination of the amino acid sequence suggests that CDC5L may be phosphorylated at up to 28 potential consensus recognition sequences for known kinases, however, the identity of actual phosphorylation sites, their role in regulating CDC5L activity, and the kinases responsible for their phosphorylation have not previously been determined. Using two-dimensional phosphopeptide mapping and nanoelectrospray mass spectrometry, we now show that CDC5L is phosphorylated on at least nine sites in vivo. We demonstrate that while CDC5L is capable of forming homodimers in vitro and in vivo, neither homodimerization nor nuclear localization is dependent on phosphorylation at these sites. Using an in vitro splicing assay, we show that phosphorylation of CDC5L at threonines 411 and 438 within recognition sequences for CDKs are required for CDC5L-mediated pre-mRNA splicing. We also demonstrate that a specific inhibitor of CDK2, CVT-313, inhibits CDC5L phosphorylation in both in vitro kinase assays and in vivo radiolabeling experiments in cycling cells. These studies represent the first demonstration of a regulatory role for phosphorylation of CDC5L, and suggest that targeting these sites or the implicated kinases may provide novel strategies for treating disorders of unguarded cellular proliferation, such as cancer.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, CA 94143-0130, USA.
authors.forename: Remo
authors.initials: R
authors.lastname: Gräub
authors.forename: Hope
authors.initials: H
authors.lastname: Lancero
authors.forename: Anissa
authors.initials: A
authors.lastname: Pedersen
authors.forename: Meihua
authors.initials: M
authors.lastname: Chu
authors.forename: Krishnan
authors.initials: K
authors.lastname: Padmanabhan
authors.forename: Xiao-Qin
authors.initials: XQ
authors.lastname: Xu
authors.forename: Paul
authors.initials: P
authors.lastname: Spitz
authors.forename: Robert
authors.initials: R
authors.lastname: Chalkley
authors.forename: Alma L
authors.initials: AL
authors.lastname: Burlingame
authors.forename: David
authors.initials: D
authors.lastname: Stokoe
authors.forename: Harold S
authors.initials: HS
authors.lastname: Bernstein
mesh_terms: D000818:Animals; D019556:COS Cells; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000737:chemistry; D002522:Chlorocebus aethiops; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D010449:Peptide Mapping; D010766:Phosphorylation; D011687:Purines / Q000494:pharmacology; D012323:RNA Processing, Post-Transcriptional; D016601:RNA-Binding Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*
chemical_list: C508357:CDC5L protein, human; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D011687:Purines; D016601:RNA-Binding Proteins; C109140:CVT 313