Transforming growth factor-beta superfamily receptors signaling occurs through the Smad family of intracellular mediators. SMAD6 is an inhibitory Smad (i-Smad) that negatively regulates signaling downstream of type I transforming growth factor-beta (PubMed:9436979, PubMed:16951688, PubMed:22275001, PubMed:9759503, PubMed:10647776, PubMed:10708948, PubMed:10708949, PubMed:30848080). Acts as a mediator of TGF-beta and BMP anti-inflammatory activities. Suppresses IL1R-TLR signaling through its direct interaction with PEL1, preventing NF-kappa-B activation, nuclear transport and NF-kappa-B-mediated expression of pro-inflammatory genes (PubMed:16951688). Blocks the BMP-SMAD1 signaling pathway by competing with SMAD4 for receptor-activated SMAD1-binding (PubMed:9436979, PubMed:30848080). Binds to regulatory elements in target promoter regions (PubMed:16491121). Interacts with NEDD4L (By similarity). Interacts with WWP1 (By similarity). Interacts with STAMBP and PRKX. Interacts with RNF111 and AXIN1. Interacts with TGF-beta type I receptor superfamily members, including ACVR1B, BMPR1B and TGFBR1. In response to BMP2, but not to TGFB treatment, interacts with SMAD1, but not with SMAD2, nor with SMAD4; this interaction may inhibit SMAD1 binding to SMAD4. Interacts with HOXC8 and HOXC9. Interacts with PELI1; this interaction interferes with PELI1 complex formation with TRAF6, IRAK1, IRAK4 and MYD88 in response to IL1B and hence negatively regulates IL1R-TLR signaling. Ubiquitous in various organs, with higher levels in lung. Isoform B is up-regulated in diseased heart tissue. Phosphorylated by BMP type 1 receptor kinase and by PRKX. Monoubiquitinated at Lys-173 by the E2/E3 hybrid ubiquitin-protein ligase UBE2O, leading to reduced binding affinity for the activated BMP type I receptor ACVR1/ALK2, thereby enhancing BMP7 and regulating adipocyte differentiation (PubMed:23455153). Ubiquitinated by WWP1 (By similarity). Ubiquitinated by RNF165, promoting proteasomal degradation, leading to enhance the BMP-Smad signaling (By similarity). Arginine methylation by PRMT1, which is recruited by BMPR2, initiates BMP-Induced signaling and induces dissociation from the BMPR1B receptor at the cell surface leading to derepress downstream Smad1/Smad5 signaling. The disease is caused by variants affecting the gene represented in this entry. SMAD6 variants may contribute to increased risk of congenital cardiovascular malformations (CVM). CVM is a major cause of mortality and morbidity in childhood. In most sporadic cases that cannot be attributed to particular malformation syndromes or teratogenic exposures, there remains a substantial excess familial risk, indicating a significant genetic contribution to disease susceptibility (PubMed:22275001). Disease susceptibility is associated with variants affecting the gene represented in this entry. Rare heterozygous SMAD6 variants are strongly associated with non-syndromic midline craniosynostosis and confer a very high risk for disease development, in the presence of a common risk allele (rs1884302) near the BMP2 locus. Disease susceptibility is associated with variants affecting the gene represented in this entry. Belongs to the dwarfin/SMAD family.