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 (By similarity). Interacts (via UIM domain) with UBQLN1 (via ubiquitin-like domain). Ubiquitously expressed, with highest levels in testis. The VHS and UIM domains mediate the interaction with ubiquitinated proteins. The SH3 domain mediates the interaction with USP8. 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 in response to IL-2, GM-CSF, EGF and PDGF. Adult mice lacking Stam and Stam2 due to inducible gene targeting exhibit significant reduction in T-cell development in the thymus and profound reduction in the peripheral mature T-cells. Belongs to the STAM family.