Abstract
SnoN (Ski-novel protein) was discovered as a nuclear proto-oncogene on the basis of its ability to induce transformation of chicken and quail embryonic fibroblasts. As a crucial negative regulator of transforming growth factor-β (TGF-β) signaling and also an activator of p53, it plays an important role in regulating cell proliferation, senescence, apoptosis, and differentiation. Recent studies of its expression patterns and functions in mouse models and mammalian cells have revealed important functions of SnoN in normal epithelial development and tumorigenesis. Evidence suggests that SnoN has both pro-oncogenic and anti-oncogenic functions by modulating multiple signaling pathways. These studies suggest that SnoN may have broad functions in the development and homeostasis of embryonic and postnatal tissues.