B cell antigen receptor cross-linking induces phosphorylation of the p21 super(ras) oncoprotein activators SHC and mSOS1 as well as assembly of complexes containing SHC, GRB-2, mSOS1, and a 145-kDa tyrosine-phosphorylated protein

• Published in: The Journal of immunology (1950) Vol. 153; no. 2; pp. 623 - 636
• Main Authors: Saxton, T M, Van Oostveen, I, Bowtell, D, Aebersold, R, Gold, M R
• Format: Journal Article
• Language: English
• Published: 01-01-1994
• ISSN: 0022-1767

Ligation of the B cell AgR activates p21 super(ras) (Ras). We have investigated the effects of AgR ligation on three proteins that have been implicated as regulators of Ras: SHC, GRB-2, and mSOS1. We show that AgR cross-linking in B cells stimulated tyrosine and serine phosphorylation of SHC. This correlated with the formation of complexes containing SHC, GRB-2, mSOS1, and an unidentified 145-kDa tyrosine-phosphorylated protein. These complexes were present in the cytosol, as well as in the membrane fraction of the cells, where Ras is located. By using a GRB-2 fusion protein to probe blots, we showed that SHC was the major protein that GRB-2 bound to in anti-Ig-stimulated B cells. Signaling by the B cell AgR stimulates phosphorylation of SHC and mSOS1 and induces the formation of membrane-associated complexes containing SHC, GRB-2, mSOS1, and a 145-kDa protein. These events may be important for activation of Ras by the AgR.