title: Activation of Mps1 promotes transforming growth factor-beta-independent Smad signaling.
abstract: The primary intracellular mediators of TGF-beta signaling are the Smad proteins. Phosphorylation of R-Smad at the C-terminal SSXS motif by the activated TGF-beta type I receptor kinase triggers a conformation change in R-Smad and facilitates complex formation between R-Smad and Smad4, which shuttle into the nucleus where they interact with DNA and other transcription factors to regulate gene expression. In an attempt to identify proteins interacting with activated Smad signaling complex, we discovered that Mps1, a protein kinase that plays important roles in normal mitotic progression and mitotic checkpoint signaling, co-purifies with this complex. We demonstrated that Smad2 and Smad3 but not Smad4 are substrates of Mps1 in vitro and in vivo. Mps1 phosphorylates Smad2 and Smad3 at the SSXS motif in their C-terminal regions in vitro and in vivo. Disruption of microtubule networks by nocodazole activates Mps1 and promotes TGF-beta-independent activation of Smad signaling. We found that Mps1 is involved in turning on Smad signaling by phosphorylating R-Smads. Our results reveal a novel functional link between Mps1 and Smads in a non-canonical Smad signaling pathway.
authors: Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309.
authors: Songcheng
authors: S
authors: Zhu
authors: Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309.
authors: Wei
authors: W
authors: Wang
authors: Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309.
authors: David C
authors: DC
authors: Clarke
authors: Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309. Electronic address: Xuedong.Liu@colorado.edu.
authors: Xuedong
authors: X
authors: Liu
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D006801:Humans; D015739:Nocodazole / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D011505:Protein-Tyrosine Kinases; D015398:Signal Transduction; D051898:Smad1 Protein / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D051898:Smad1 Protein; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D004247:DNA; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; C075840:TTK protein, human; D015739:Nocodazole