Abstract
A 120-kDa protein that is tyrosine-phosphorylated upon antigen receptor ligation in B lymphocytes has been identified as the product of the c-cbl protooncogene. Tyrosine phosphorylation of Cbl depends on the efficient association of membrane immunoglobulin heavy chains with the Ig alpha/beta heterodimer but is unimpaired in splenic B cells from the Xid mouse. Cross-linking of membrane IgM and membrane IgG, but not of CD40, leads to the tyrosine phosphorylation of Cbl. In receptor-ligated B lymphocytes, p120cbl associates with an 85-kDa protein that has been identified as the 85-kDa subunit of phosphatidylinositol 3-kinase.
Highlights
The antigen receptor on B lymphocytes is made up of membrane immunoglobulins associated with the Ig␣/ heterodimer [1, 2]
Since the tyrosine phosphorylation of Cbl is an early event downstream of the engagement of a number of mitogenic receptors, we sought to identify proteins that associate with Cbl after the initiation of signal transduction
We have demonstrated here that an 85-kDa protein associates with Cbl following B cell receptor ligation and that this 85-kDa protein is the p85 subunit of PI 3-kinase
Summary
The antigen receptor on B lymphocytes is made up of membrane immunoglobulins associated with the Ig␣/ heterodimer [1, 2]. Our studies suggest that a major role of Cbl in B cells may be the recruitment and activation of PI 3-kinase following antigen receptor ligation.
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