The kinase activity of the Ser/Thr kinase BUB1 promotes TGF-β signaling

Sci Signal. 2015 Jan 6;8(358):ra1. doi: 10.1126/scisignal.2005379.

Abstract

Transforming growth factor-β (TGF-β) signaling regulates cell proliferation and differentiation, which contributes to development and disease. Upon binding TGF-β, the type I receptor (TGFBRI) binds TGFBRII, leading to the activation of the transcription factors SMAD2 and SMAD3. Using an RNA interference screen of the human kinome and a live-cell reporter for TGFBR activity, we identified the kinase BUB1 (budding uninhibited by benzimidazoles-1) as a key mediator of TGF-β signaling. BUB1 interacted with TGFBRI in the presence of TGF-β and promoted the heterodimerization of TGFBRI and TGFBRII. Additionally, BUB1 interacted with TGFBRII, suggesting the formation of a ternary complex. Knocking down BUB1 prevented the recruitment of SMAD3 to the receptor complex, the phosphorylation of SMAD2 and SMAD3 and their interaction with SMAD4, SMAD-dependent transcription, and TGF-β-mediated changes in cellular phenotype including epithelial-mesenchymal transition (EMT), migration, and invasion. Knockdown of BUB1 also impaired noncanonical TGF-β signaling mediated by the kinases AKT and p38 MAPK (mitogen-activated protein kinase). The ability of BUB1 to promote TGF-β signaling depended on the kinase activity of BUB1. A small-molecule inhibitor of the kinase activity of BUB1 (2OH-BNPP1) and a kinase-deficient mutant of BUB1 suppressed TGF-β signaling and formation of the ternary complex in various normal and cancer cell lines. 2OH-BNPP1 administration to mice bearing lung carcinoma xenografts reduced the amount of phosphorylated SMAD2 in tumor tissue. These findings indicated that BUB1 functions as a kinase in the TGF-β pathway in a role beyond its established function in cell cycle regulation and chromosome cohesion.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Line, Tumor
  • Dimerization
  • Fluorescent Antibody Technique
  • Gene Knockdown Techniques
  • High-Throughput Screening Assays
  • Humans
  • Immunohistochemistry
  • Immunoprecipitation
  • Mice
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • RNA Interference
  • RNA, Small Interfering / genetics
  • Receptors, Transforming Growth Factor beta / chemistry
  • Receptors, Transforming Growth Factor beta / metabolism*
  • Signal Transduction / genetics
  • Signal Transduction / physiology*
  • Smad Proteins, Receptor-Regulated / metabolism*
  • Transforming Growth Factor beta / physiology*

Substances

  • RNA, Small Interfering
  • Receptors, Transforming Growth Factor beta
  • Smad Proteins, Receptor-Regulated
  • Transforming Growth Factor beta
  • BUB1 protein, human
  • Protein-Serine-Threonine Kinases