Regulation of c-fgr proto-oncogene expression in Burkitt's lymphoma cells: effect of interferon treatment and relationship to EBV status and c-myc mRNA levels.

The proto-oncogene c-fgr is expressed in transformed human B lymphoid cell lines and has been reported to be induced in cells infected with the Epstein-Barr virus (EBV). We have compared the levels of c-fgr mRNA in several B cell lines and have examined the effects of interferon-induced changes in growth rate of Daudi cells on the concentration of this mRNA. High levels were found in exponentially growing EBV-positive Raji and Daudi cells but the amounts in B95-8 and P3HR-1 cells (also EBV-positive) were lower than in the EBV-negative cell line Ramos. Growth inhibition of Daudi cells by interferon-alpha is preceded by a reduction in c-fgr expression, with a 56% decrease observed within 6 h. The differences in the amounts of c-fgr mRNA in the various cell lines and in control versus interferon-treated cells are similar to the differences in the c-myc mRNA contents of these cells. These results indicate that c-fgr expression bears little relationship to the EBV status of B lymphoid cell lines but may play a role, in conjunction with c-myc expression, in growth regulation by interferons. Other conditions which influence Daudi cell proliferation, such as treatment with a phorbol ester or growth to high cell density, also inhibit c-fgr expression but to a lesser extent than interferon treatment.