Involved in intracellular signal transduction mediated by cytokines and growth factors. Upon IL-2 and GM-CSL stimulation, it plays a role in signaling leading to DNA synthesis and MYC induction. May also play a role in T-cell development. Involved in down-regulation of receptor tyrosine kinase via multivesicular body (MVBs) when complexed with HGS (ESCRT-0 complex). The ESCRT-0 complex binds ubiquitin and acts as sorting machinery that recognizes ubiquitinated receptors and transfers them to further sequential lysosomal sorting/trafficking processes (By similarity). Component of the ESCRT-0 complex composed of STAM or STAM2 and HGS. Part of a complex at least composed of HSG, STAM2 and EPS15. Interacts with JAK2 and JAK3. Interacts with ubiquitinated proteins and the deubiquitinating enzyme USP8/UBPY. Interacts (via the via the PxVxL motif) with CBX5; the interaction is direct. Interacts with VPS37C. Interacts with ubiquitin; the interaction is direct. Interacts (via UIM domain) with UBQLN1 (via ubiquitin-like domain) (By similarity). Contains one Pro-Xaa-Val-Xaa-Leu (PxVxL) motif, which is required for interaction with chromoshadow domains. This motif requires additional residues -7, -6, +4 and +5 of the central Val which contact the chromoshadow domain. Phosphorylated. Belongs to the STAM family.