SH3P7 is a cytoskeleton adapter protein and is coupled to signal transduction from lymphocyte antigen receptors

Lymphocytes respond to antigen receptor engagement with tyrosine phosphoryl ation of many cellular proteins, some of which have been identified and fun ctionally characterized. Here we describe SH3P7, a novel substrate protein for Src and Syk family kinases. SH3P7 migrates in sodium dodecyl sulfate-po lyacrylamide gel electrophoresis as a 55-kDa protein that is preferentially expressed in brain, thymus, and spleen. It contains multiple amino acid se quence motifs, including two consensus tyrosine phosphorylation sites of th e YXXP type and one SH3 domain. A region of sequence similarity, which we n amed SCAD, was found in SH3P7 and three actin-binding proteins. The SCAD re gion may represent a new type of protein-protein interaction domain that me diates binding to actin. Consistent with this possibility, SH3P7 colocalize s with actin filaments of the cytoskeleton. Altogether, our data implicate SH3P7 as an adapter protein which links antigen receptor signaling to compo nents of the cytoskeleton.