FORMATION OF SHC GRB2- AND CRK ADAPTER COMPLEXES CONTAINING TYROSINE-PHOSPHORYLATED CBL UPON STIMULATION OF THE B-CELL ANTIGEN RECEPTOR/

B-cell antigen receptor (BCR) stimulation induces tyrosine phosphoryla tion of the She adaptor protein and its association with Grb2. The Shc /Grb2 complex may be involved in Ras activation, since Grb2 interacts with the guanine nucleotide exchange factor Sos. We reveal here an add itional complexity of the BCR-induced Shc/Grb2 complex: it contains ty rosine phosphorylated proteins of 130, 110 and 75 kDa. The 130 kDa mol ecule inducibly associates with She, while the 75 kDa protein interact s with the carboxy-terminal SH3 domain of Grb2. The 110 kDa molecule i s defined as Cbl, the product of the c-cbl oncogene, which is strongly phosphorylated on tyrosine upon BCR stimulation. Cbl constitutively i nteracts with the SH3 domains of Grb2, with a preference for the amino -terminal domain, and is in this way recruited to She upon BCR stimula tion. Immunodepletion studies showed that Grb2-associated Cbl can be p hosphorylated by BCR-induced tyrosine kinases independent of a Shc/Grb 2 interaction. This indicates that the BCR can also couple to a Grb2 c omplex without the involvement of She. Cbl not only interacts with Grb 2, but also with the adaptor protein Crk. In contrast to its constitut ive interaction with Grb2, tyrosine-phosphorylated Cbl only associates with Crk after BCR stimulation. In summary, we observe that the BCR a ctivates Shc/Grb2-, Grb2- and Crk adaptor complexes of distinct compos ition, which may allow selective coupling to different signal transduc tion cascades. Cbl participates in all three adaptor complexes and is tyrosine phosphorylated upon BCR stimulation, pointing to a central ro le for this molecule in the regulation of antigen receptor-induced B c ell responses.