The function of ENSG00000126264 (HCST, hematopoietic cell signal transducer) is as follows. Transmembrane adapter protein which associates with KLRK1 to form an activation receptor KLRK1-HCST in lymphoid and myeloid cells; this receptor plays a major role in triggering cytotoxicity against target cells expressing cell surface ligands such as MHC class I chain- related MICA and MICB, and UL16-binding proteins (ULBPs); these ligands are up-regulated by stress conditions and pathological state such as viral infection and tumor transformation. Functions as a docking site for PI3-kinase PIK3R1 and GRB2. Interaction of ULBPs with KLRK1-HCST triggers calcium mobilization and activation of the PIK3R1, MAP2K/ERK, and JAK2/STAT5 signaling pathways. Both PIK3R1 and GRB2 are required for full KLRK1-HCST-mediated activation and ultimate killing of target cells. In NK cells, KLRK1-HCST signaling directly induces cytotoxicity and enhances cytokine production initiated via DAP12/TYROBP-associated receptors. In T-cells, it provides primarily costimulation for TCR- induced signals. KLRK1-HCST receptor plays a role in immune surveillance against tumors and is required for cytolysis of tumors cells; indeed, melanoma cells that do not express KLRK1 ligands escape from immune surveillance mediated by NK cells. {ECO:0000269|PubMed:10426994, ECO:0000269|PubMed:10528161, ECO:0000269|PubMed:11015446, ECO:0000269|PubMed:11777960, ECO:0000269|PubMed:12740575, ECO:0000269|PubMed:12740576, ECO:0000269|PubMed:16002667, ECO:0000269|PubMed:16339517, ECO:0000269|PubMed:16582911, ECO:0000269|PubMed:18097042}.