title: An essential role of Pak1 phosphorylation of SHARP in Notch signaling.
abstract: The p21-activated kinases (Paks), an evolutionarily conserved family of serine/threonine kinases, play an important role in cytoskeletal reorganization in mammalian cells. The Notch signaling pathway plays an important role in the determination of cell fate/differentiation in a number of organs. Notch signaling is a complex process, and the mechanism by which Notch regulates multiple cellular processes is intriguing. The expression of both Notch and Pak1 has been shown to be deregulated in several human cancers. Using yeast two-hybrid screening, we identified SHARP, one of the Notch signaling components, as a Pak1-interacting protein. We found that SHARP is a physiologic interacting substrate of Pak1, and that this interaction enhances SHARP-mediated repression of Notch target genes. Pak1 phosphorylation sites in SHARP were mapped to Ser3486 and Thr3568 within the SHARP repression domain. Mutation of Pak1 phosphorylation sites in SHARP, inhibition of Pak1 functions by a Pak1-autoinhibitory fragment (amino acids 83-149), or expression of Pak1-specific siRNA interfered with SHARP-mediated repression of Notch target reporter gene activation. These results demonstrate that Pak1-SHARP interaction plays an essential role in enhancing the corepressor functions of SHARP, thereby modulating Notch signaling in human cancer cells.
authors.affiliation: Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
authors.forename: Ratna K
authors.initials: RK
authors.lastname: Vadlamudi
authors.forename: Bramanandam
authors.initials: B
authors.lastname: Manavathi
authors.forename: Rajesh R
authors.initials: RR
authors.lastname: Singh
authors.forename: Diep
authors.initials: D
authors.lastname: Nguyen
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.forename: Rakesh
authors.initials: R
authors.lastname: Kumar
mesh_terms: D016475:3T3 Cells; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D006801:Humans; D051379:Mice; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D054462:p21-Activated Kinases
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D017346:Protein Serine-Threonine Kinases; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface; D012694:Serine; D014157:Transcription Factors; D054462:p21-Activated Kinases; C422085:BHLHE41 protein, human; C497761:NOTCH1 protein, human; C497762:Notch1 protein, mouse; C515903:PAK1 protein, human; C515905:Pak1 protein, mouse