PHYSICAL AND FUNCTIONAL ASSOCIATION OF THE CBL PROTOONCOGENE PRODUCT WITH AN SRC-FAMILY PROTEIN-TYROSINE KINASE, P53 56(LYN), IN THE B-CELLANTIGEN RECEPTOR-MEDIATED SIGNALING/

To identify novel signal transducers involved in signaling mediated by the Src-family protein tyrosine kinases (PTKs), we used a yeast two-h ybrid system with a probe corresponding to the regulatory region of p5 6(lyn), a member of Src-family PTKs. One of the isolated clones contai ned the COOH-terminal 470 amino acid residues of p120(c-cbl), the prod uct of the cellular homologue of the v-cbl retroviral oncogene. p120(c -cbl) is a cytoplasmic protein with nuclear protein-like motifs. Here we show in vivo association of p120(c-cbl) with p53/56(lyn). After sti mulation of the B cell antigen receptor (BCR), p120(c-cbl) was rapidly tyrosine phosphorylated. Studies with lyn- or syk-negative chicken B cells demonstrated that p53/56(lyn), but not p72(syk), was crucial for tyrosine phosphorylation of p120(c-cbl) upon stimulation of the BCR. We also show the importance of p59(fyn) in tyrosine phosphorylation of p120(c-cbl) in the T-cell receptor-mediated signaling, using fyn-over expressing T cell hybridomas and splenic T cells from fyn-deficient mi ce. These results suggest that p120(c-cbl) is an important substrate o f Src-family PTKs in the intracellular signaling mediated by the antig en receptors.