Adapter protein, which negatively regulates T-cell receptor (TCR) signaling. Inhibits T-cell antigen-receptor induced activation of nuclear factor of activated T-cells. Involved in the negative regulation of positive selection and mitosis of T-cells. May act by linking signaling proteins such as ZAP70 with CBL, leading to a CBL dependent degradation of signaling proteins. Homodimer. Interacts with phosphorylated CBL, SYK and LAT. Homodimerization and interaction with phosphorylated CBL occurs via its C-terminal domain (By similarity). Interacts with PDGFRB and EPHA2. Interacts with phosphorylated proteins ZAP70; CD3Z; VAV1 and LCP2 via its SH2 domain. Colocalizes with endosomes. Predominantly expressed in lymphoid tissues. Highly expressed in spleen, thymus and lymph nodes. Weakly expressed in lung and brain. Expressed in T-cells and at low level in B-cells. Expressed during thymocyte maturation. Weakly expressed in CD4(-) CD8(-) thymocytes, strongly expressed in CD4(+) CD8(+) thymocytes, while expression decreases in more mature cells. The C-terminal domain is essential for the homodimerization and the interaction with CBL. While the interaction with CBL is apparently mediated via the hydrophobic region of this domain, the highly charged region is apparently required for the homodimerization (By similarity). SLA deficient mice show a strong up-regulation of TCR and CD5 at the CD4(+) CD8(+) stage, and an enhanced positive selection in T-cells.