Conversion of a human B cell lymphoma line by Epstein-Barr virus is associated with increased tyrosine phosphorylation of a 50 kilodalton cytosolic protein.

Infection of human B cells by Epstein-Barr virus (EBV) causes transformation to immortalized lymphoblastoid cells capable of continuous proliferation. To identify biochemical changes induced by EBV infection of B cells, we have utilized isogenic EBV-positive and -negative B cell lymphoma lines as a model to determine whether EBV induces protein tyrosine phosphorylation. By utilizing two different methods, immunoblotting with phosphotyrosine antibodies and phosphoamino acid analysis, it was shown that the presence of EBV in these cells was reversibly associated with increased phosphorylation of a 50 kilodalton cytosolic protein on tyrosine residues. The characteristics of this protein were not consistent with any known EBV-encoded protein that is expressed in latency, and thus it likely represents a cellular protein that is phosphorylated by an endogenous tyrosine kinase. These results suggest that EBV induces protein tyrosine phosphorylation in human B cells, and this may represent an important event in the transformation of B lymphocytes by EBV.