MH2 domain of transcriptional factor SMAD3
[SMAD3_HUMAN] Defects in SMAD3 may be a cause of colorectal cancer (CRC) [MIM:114500]. Defects in SMAD3 are the cause of Loeys-Dietz syndrome 3 (LDS3) [MIM:613795]. An aortic aneurysm syndrome with widespread systemic involvement. The disorder is characterized by the triad of arterial tortuosity and aneurysms, hypertelorism, and bifid uvula or cleft palate. Patients with LDS3 also manifest early-onset osteoarthritis. They lack craniosynostosis and mental retardation. Note=SMAD3 mutations have been reported to be also associated with thoracic aortic aneurysms and dissection (TAAD) (PubMed:21778426). This phenotype is distinguised from LDS3 by having aneurysms restricted to thoracic aorta. As individuals carrying these mutations also exhibit aneurysms of other arteries, including abdominal aorta, iliac, and/or intracranial arteries (PubMed:21778426), they have been classified as LDS3 by the OMIM resource. 
[SMAD3_HUMAN] Receptor-regulated SMAD (R-SMAD) that is an intracellular signal transducer and transcriptional modulator activated by TGF-beta (transforming growth factor) and activin type 1 receptor kinases. Binds the TRE element in the promoter region of many genes that are regulated by TGF-beta and, on formation of the SMAD3/SMAD4 complex, activates transcription. Also can form a SMAD3/SMAD4/JUN/FOS complex at the AP-1/SMAD site to regulate TGF-beta-mediated transcription. Has an inhibitory effect on wound healing probably by modulating both growth and migration of primary keratinocytes and by altering the TGF-mediated chemotaxis of monocytes. This effect on wound healing appears to be hormone-sensitive. Regulator of chondrogenesis and osteogenesis and inhibits early healing of bone fractures (By similarity). Positively regulates PDPK1 kinase activity by stimulating its dissociation from the 14-3-3 protein YWHAQ which acts as a negative regulator.          
Publication Abstract from PubMed
Smad3 transduces the signals of TGF-betas, coupling transmembrane receptor kinase activation to transcriptional control. The membrane-associated molecule SARA (Smad Anchor for Receptor Activation) recruits Smad3 for phosphorylation by the receptor kinase. Upon phosphorylation, Smad3 dissociates from SARA and enters the nucleus, in which its transcriptional activity can be repressed by Ski. Here, we show that SARA and Ski recognize specifically the monomeric and trimeric forms of Smad3, respectively. Thus, trimerization of Smad3, induced by phosphorylation, simultaneously activates the TGF-beta signal by driving Smad3 dissociation from SARA and sets up the negative feedback mechanism by Ski. Structural models of the Smad3/SARA/receptor kinase complex and Smad3/Ski complex provide insights into the molecular basis of regulation.
Smad3 allostery links TGF-beta receptor kinase activation to transcriptional control.,Qin BY, Lam SS, Correia JJ, Lin K Genes Dev. 2002 Aug 1;16(15):1950-63. PMID:12154125
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.