SMIF, a Smad4-interacting protein that functions as a co-activator in TGFbeta signalling.
Proteins of the transforming growth factor beta(TGFbeta) superfamily regulate diverse cellular responses, including cell growth and differentiation. After TGFbeta stimulation, receptor-associated Smads are phosphorylated and form a complex with the common mediator Smad4. Here, we report the cloning of SMIF, a ubiquitously expressed, Smad4-interacting transcriptional co-activator. SMIF forms a TGFbeta/bone morphogenetic protein 4 (BMP4)-inducible complex with Smad4, but not with others Smads, and translocates to the nucleus in a TGFbeta/BMP4-inducible and Smad4-dependent manner. SMIF possesses strong intrinsic TGFbeta-inducible transcriptional activity, which is dependent on Smad4 in mammalian cells and requires p300/CBP. A point mutation in Smad4 abolished binding to SMIF and impaired its activity in transcriptional assays. Overexpression of wild-type SMIF enhanced expression of TGFbeta/BMP regulated genes, whereas a dominant-negative SMIF mutant suppressed expression. Furthermore, dominant-negative SMIF is able to block TGFbeta-induced growth inhibition. In a knockdown approach with morpholino-antisense oligonucleotides targeting zebrafish SMIF, severe but distinct phenotypic defects were observed in zebrafish embryos. Thus, we propose that SMIF is a crucial activator of TGFbeta signalling.
Bai
Ren-Yuan
RY
Department of Internal Medicine III, Laboratory of Leukemogenesis, Technical University of Munich, Ismaningerstrasse 22, 81675 Munich, Germany.
Koester
Christina
C
Ouyang
Tao
T
Hahn
Stephan A
SA
Hammerschmidt
Matthias
M
Peschel
Christian
C
Duyster
Justus
J
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics; D004722:Endoribonucleases; D018390:Gene Targeting; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D020319:Oligodeoxyribonucleotides, Antisense / Q000235:genetics / Q000494:pharmacology; D017354:Point Mutation; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D015027:Zebrafish / Q000002:abnormalities / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics* / Q000378:metabolism*
C525809:BMP4 protein, human; C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D020319:Oligodeoxyribonucleotides, Antisense; C497796:SMAD4 protein, human; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D029961:Zebrafish Proteins; C525813:bmp4 protein, zebrafish; C466281:smad4-interacting protein SMIF, Zebrafish; C490809:smad4a protein, zebrafish; D004722:Endoribonucleases; C466280:smad4-interacting protein SMIF, mouse; C466279:DCP1A protein, human