May have regulatory role in cell division or differentiation in response to extracellular signals. Interacts with CPNE4 (via VWFA domain) (By similarity). Interacts with SMAD2, SMAD3 and RNF111 (PubMed:17591695). Isoform 1 interacts with WWP1 (PubMed:15221015). Isoform SNON and isoform SNOA are widely expressed. Highest expression is found in skeletal muscle, followed by placenta and lung. Lowest expression in heart, brain and pancreas. Isoform SNOI expression is restricted to skeletal muscle. Ubiquitinated by RNF111 and RNF165, promoting proteasomal degradation, leading to enhance the BMP-Smad signaling. Belongs to the SKI family.