Involved in intracellular signal transduction mediated by cytokines and growth factors. When associated with STAM, it suppresses DNA signaling upon stimulation by IL-2 and GM-CSF. Could be a direct effector of PI3-kinase in vesicular pathway via early endosomes and may regulate trafficking to early and late endosomes by recruiting clathrin. May concentrate ubiquitinated receptors within clathrin-coated regions. Involved in down-regulation of receptor tyrosine kinase via multivesicular body (MVBs) when complexed with STAM (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. May contribute to the efficient recruitment of SMADs to the activin receptor complex. Involved in receptor recycling via its association with the CART complex, a multiprotein complex required for efficient transferrin receptor recycling but not for EGFR degradation. Component of the ESCRT-0 complex composed of STAM or STAM2 and HGS. Part of a complex at least composed of HSG, STAM2 (or probably STAM) and EPS15 (PubMed:12551915). Interacts with STAM (PubMed:9407053). Interacts with STAM2 (By similarity). Interacts with EPS15; the interaction is direct, calcium-dependent and inhibited by SNAP25 (By similarity). Identified in a complex with STAM and LITAF (PubMed:23166352). Found in a complex with STAM and E3 ligase ITCH and DTX3L (PubMed:24790097). 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 (PubMed:24790097). Interacts with NF2; the interaction is direct (PubMed:10861283). Interacts with ubiquitin; the interaction is direct (By similarity). Interacts with VPS37C (PubMed:15509564). Interacts with SMAD1, SMAD2 and SMAD3 (By similarity). Interacts with TSG101; the interaction mediates the association with the ESCRT-I complex (PubMed:21070952). Interacts with SNAP25; the interaction is direct and decreases with addition of increasing concentrations of free calcium (By similarity). Interacts with SNX1; the interaction is direct (By similarity). Component of a 550 kDa membrane complex at least composed of HGS and SNX1 but excluding EGFR (By similarity). Interacts with TRAK1 (PubMed:18675823). Interacts with TRAK2 (By similarity). Component of the CART complex, at least composed of ACTN4, HGS/HRS, MYO5B and TRIM3 (PubMed:15772161). Interacts (via UIM domain) with UBQLN1 (via ubiquitin-like domain) (By similarity). Interacts with ARRDC3 (PubMed:23208550). Identified in a complex containing at least ARRDC4, AVPR2 and HGS (PubMed:23236378). Interacts with LAPTM4B; promotes HGS ubiquitination (PubMed:25588945). Colocalizes with UBQLN1 in ubiquitin-rich cytoplasmic aggregates that are not endocytic compartments. Ubiquitous expression in adult and fetal tissues with higher expression in testis and peripheral blood leukocytes. Has a double-sided UIM that can bind 2 ubiquitin molecules, one on each side of the helix. The FYVE-type zinc finger domain mediates interactions with phosphatidylinositol 3-phosphate in membranes of early endosomes and penetrates bilayers. The FYVE domain insertion into PtdIns(3)P-enriched membranes is substantially increased in acidic conditions. Phosphorylated on Tyr-334. A minor site of phosphorylation on Tyr-329 is detected (By similarity). Phosphorylation occurs in response to EGF, IL-2, GM-CSF and HGF. Ubiquitinated (PubMed:25588945). Ubiquitinated by ITCH (PubMed:14602072, PubMed:24790097). Dubious isoform produced through aberrant splice sites.