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 (PubMed:19278655). Probably part of a complex at least composed of HSG, STAM and EPS15 (By similarity). Found in a complex with HGS and E3 ligase ITCH and DTX3L (By similarity). Interacts with E3 ligase DTX3L; the interaction brings together STAM and HSG, promotes their recruitment to early endosomes and decreases STAM and HGS ubiquitination by ITCH (By similarity). Interacts with STAMBP/AMSH (By similarity). Interacts with PDGFRB (By similarity). Interacts with LITAF; the interaction is direct (By similarity). Identified in a complex with HGS and LITAF (By similarity). Interacts with HAVCR1 (By similarity). Ubiquitously expressed. Enriched expression in synaptic vesicles. No change during brain development. The VHS domain mediates high-avidity binding to Lys63-linked and Lys48-linked polyubiquitinated cargos. Phosphorylated on Tyr-198. Phosphorylated in response to IL2, IL3, IL4, IL7, CSF2/GM-CSF, EGF and PDGFB. Phosphorylated by activated PDGFRB (By similarity). Ubiquitinated by ITCH. Mice display disappearance of hippocampal CA3 pyramidal neurons as well as growth retardation in the third week after birth. 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.