Ski-interacting protein interacts with Smad proteins to augment transforming growth factor-beta-dependent transcription.
Transforming growth factor-beta (TGF-beta) signaling requires the action of Smad proteins in association with other DNA-binding factors and coactivator and corepressor proteins to modulate target gene transcription. Smad2 and Smad3 both associate with the c-Ski and Sno oncoproteins to repress transcription of Smad target genes via recruitment of a nuclear corepressor complex. Ski-interacting protein (SKIP), a nuclear hormone receptor coactivator, was examined as a possible modulator of transcriptional regulation of the TGF-beta-responsive promoter from the plasminogen activator inhibitor gene-1. SKIP augmented TGF-beta-dependent transactivation in contrast to Ski/Sno-dependent repression of this reporter. SKIP interacted with Smad2 and Smad3 proteins in vivo in yeast and in mammalian cells through a region of SKIP between amino acids 201-333. In vitro, deletion of the Mad homology domain 2 (MH2) domain of Smad3 abrogated SKIP binding, like Ski/Sno, but the MH2 domain of Smad3 alone was not sufficient for protein-protein interaction. Overexpression of SKIP partially overcame Ski/Sno-dependent repression, whereas Ski/Sno overexpression attenuated SKIP augmentation of TGF-beta-dependent transcription. Our results suggest a potential mechanism for transcriptional control of TGF-beta signaling that involves the opposing and competitive actions of SKIP and Smad MH2-interacting factors, such as Ski and/or Sno. Thus, SKIP appears to modulate both TGF-beta and nuclear hormone receptor signaling pathways.
Bone & Mineral Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales 2010, Australia. g.leong@garvan.unsw.edu.au
G M
GM
Leong
N
N
Subramaniam
J
J
Figueroa
J L
JL
Flanagan
M J
MJ
Hayman
J A
JA
Eisman
A P
AP
Kouzmenko
D000818:Animals; D019556:COS Cells; D004268:DNA-Binding Proteins / Q000502:physiology*; D009687:Nuclear Proteins / Q000502:physiology*; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000502:physiology*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000502:physiology*
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta