Tom1L-1 is a 476 amino acid Golgi apparatus protein belonging to the TOM1 family and is a member of the multivesicular body (MVB) sorting machinery. Containing a GAT domain and a VHS domain, Tom1L-1 interacts with Fyn, GRB2, PI 3-kinase p85?and various signaling proteins when phosphorylated. GAT domain of Tom1L1 binds ubiquitin, suggesting participation in the sorting of ubiquitinated proteins into MVBs. Tom1L-1 may act as an adapter protein involved in signaling pathways and may promote Fyn activation, possibly by disrupting intramolecular SH3-dependent interactions. As an interactor and a substrate of Src tyrosine kinases (SFK), Tom1L1 is considered a novel mechanism involved in negative regulation of SFK mitogenic and transforming signals. Tom1L1 modulates SFK partitioning at the plasma membrane and downregulates Src kinases in an endosomal-dependent manner. It is suggested that Tom1L-1 functions as an anti-oncogene by inhibiting the formation of squamous cell carcinomas in skin.