Smad4 protein stability is regulated by ubiquitin ligase SCF beta-TrCP1.
Smad4 is a key intracellular mediator for the transforming growth factor-beta (TGF-beta) superfamily of growth factors and is also an important tumor suppressor. The receptor-regulated Smad (R-Smad) proteins are regulated by ubiquitin-mediated degradation, yet the precise control of Smad4 protein stability is unclear. We have identified SCF(beta-TrCP1), a ubiquitin (E3) ligase, as a critical determinant for the protein degradation of Smad4 protein. F-box protein beta-TrCP1 in this E3 ligase interacts with Smad4 both in yeast and in mammalian cells, but has no interaction with Smad2 and has weak interaction with Smad3. The beta-TrCP1/Smad3 interaction was abolished by Smad4 gene silencing, indicating the interaction is indirect and is through Smad4. Ectopic expression of SCF complex containing beta-TrCP1 is sufficient to induce the ubiquitination and degradation of Smad4. Furthermore, small interfering RNA-triggered endogenous beta-TrCP1 suppression increases the expression of Smad4 protein. Consistent with these results, cells that overexpress the SCF complex display an inhibited TGF-beta-dependent transcriptional activity and an impaired cell cycle arrest function. Thus, SCF(beta-TrCP1) abrogates TGF-beta function in vivo by decreasing Smad4 stability.
Department of Pathology, University of Alabama at Birmingham, School of Medicine, Birmingham, Alabama 35294, USA.
Mei
M
Wan
Yi
Y
Tang
Ewan M
EM
Tytler
Chongyuan
C
Lu
Bingwen
B
Jin
Selwyn M
SM
Vickers
Lei
L
Yang
Xingming
X
Shi
Xu
X
Cao
D015153:Blotting, Western; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D015536:Down-Regulation; D020868:Gene Silencing; D006801:Humans; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000737:chemistry / Q000502:physiology*; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D013997:Time Factors; D015534:Trans-Activators / Q000737:chemistry* / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D025801:Ubiquitin / Q000378:metabolism
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D025801:Ubiquitin; D044843:SKP Cullin F-Box Protein Ligases