CD19 regulates signal transduction mediated by RP105. (A) Protein tyrosine phosphorylation following RP105 cross-linking. Parental A20 and CD19– A20 cells (4 × 105/lane) were incubated with anti-RP105 Abs for the indicated times. Cell lysates were subjected to SDS-PAGE and transferred onto membranes for antiphosphotyrosine (pTyr) immunoblotting. Molecular weight standards (kDa) are shown on the right. The membrane was reprobed with anti-Vav Abs. (B) Lyn and (C) Vav tyrosine phosphorylation in A20 cells. Parental and CD19– A20 cells (3 × 107/lane) were incubated with anti-RP105 Abs, detergent lysed, and incubated with protein G beads and either anti-Lyn or anti-Vav Abs. Immunoprecipitated proteins were subjected to SDS-PAGE and transferred onto membranes for anti-pTyr immunoblotting. These results are representative of those obtained in 3 independent experiments.
