title: Phosphorylation regulation of the interaction between Smad7 and activin type I receptor.
abstract: Signal transduction of activin, one of the members in the transforming growth factor-beta superfamily, is initiated by ligand binding with two distinct membrane receptors (type II and type I) followed by activation of Smad2 or Smad3. We report here that activin-induced signaling is negatively regulated by another Smad molecule, Smad7. When expressed in Chinese hamster ovary cells, Smad7 inhibited the transcriptional response induced by either activin treatment or a constitutively active activin type I receptor (ALK-4). In addition, Smad7 also inhibited mouse FAST-2-mediated transactivation of the Xenopus Mix.2 promoter stimulated by the constitutively active ALK-4. Smad7 was able to directly associate with ALK-4 and this association was dependent on the phosphorylation of the type I receptor in its GS domain by activin type II receptors. Expression of kinase defective activin type II receptors decreased the association of Smad7 with ALK-4. Correspondingly, Smad7 bound poorly to a mutant ALK-4 bearing serine to alanine substitutions in four putative phosphorylation sites in its GS domain. These studies not only illustrated the counter regulatory function of Smad7 on activin signaling, but also indicated the involvement of phosphorylation at activin type I receptor in the inhibitory action of Smad7.
authors.affiliation: Department of Medical and Molecular Genetics and the Walther Oncology Center, Indiana University School of Medicine, and the Walther Cancer Institute, 975 West Walnut Street, IB130, Indianapolis, IN 46202, USA.
authors.forename: Xubao
authors.initials: X
authors.lastname: Liu
authors.forename: Raman P
authors.initials: RP
authors.lastname: Nagarajan
authors.forename: Wylie
authors.initials: W
authors.lastname: Vale
authors.forename: Yan
authors.initials: Y
authors.lastname: Chen
mesh_terms: D030201:Activin Receptors, Type I / Q000235:genetics / Q000378:metabolism*; D030301:Activin Receptors, Type II / Q000235:genetics / Q000378:metabolism; D028341:Activins / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D003001:Cloning, Molecular; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D051858:Forkhead Transcription Factors; D015870:Gene Expression; D017930:Genes, Reporter; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011485:Protein Binding / Q000502:physiology; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary / Q000502:physiology; D011506:Proteins; D051381:Rats; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051906:Smad7 Protein; D013329:Structure-Activity Relationship; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D014157:Transcription Factors / Q000494:pharmacology; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; C510350:FOXH1 protein, human; D051858:Forkhead Transcription Factors; C491117:Foxh1 protein, mouse; D011506:Proteins; D018125:Receptors, Transforming Growth Factor beta; C497806:SMAD7 protein, human; D051906:Smad7 Protein; C497808:Smad7 protein, rat; D015534:Trans-Activators; D014157:Transcription Factors; D028341:Activins; D017346:Protein Serine-Threonine Kinases; C425423:ACVR1 protein, human; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625843:Tgfbr1 protein, rat