Could be a T-cell-specific adapter protein involved in the control of T-cell activation. May play a role in the CD4-p56-LCK-dependent signal transduction pathway. Could also play an important role in normal and pathological angiogenesis. Could be an adapter protein that facilitates and regulates interaction of KDR with effector proteins important to endothelial cell survival and proliferation. Interacts with KDR. Interacts with TXK and ITK (By similarity). Expression limited to tissues of the immune system and, in particular, activated T-cells. Expressed in peripheral blood leukocytes, thymus and spleen. Much lower expression or undetectable, in brain, placenta, skeletal muscle, prostate, testis, ovary, small intestine, and colon. Expressed at low levels in unstimulated T-cells, but not expressed in normal resting or activated B-cells. According to PubMed:10692392, expression is not restricted to activated T-cells, but strongly expressed in blood cell lineages, the endothelium and other cell and tissue types, such as heart, lung, and liver. Rapidly induced after activation of T-cells. However, the gene continues to be expressed in long-term cultures of activated T-cells. Phosphorylated on tyrosine residues.