Defective HLA class II expression in a regulatory mutant is partially complemented by activated ras oncogenes

The human B-cell line RJ2.2.5, derived by mutagenesis from a Burkitt lymphoma cell line and selected for loss of HLA class II antigen expression, was infected with recombinant retroviruses containing either the Harvey murine sarcoma virus oncogene v-Ha-ras or the human neuroblastoma homolog NRAS. Both activated ras genes partially complemented the regulatory defect in RJ2.2.5 and specifically increased the expression of the DR and DQ subsets of HLA class II genes. Blot-hybridization analysis and RNase mapping indicated that HLA-DQ alpha-chain mRNA in the infected cell lines was increased to a level at least 50% that of the parent B-cell line, Raji. The levels of HLA-DR and -DQ beta-chain RNA also were increased but to a lesser extent. In contrast, we detected no effect of ras on the quantities of other class II, class I, or invariant-chain mRNAs. Fluorescence-activated cell sorter analysis with antibodies recognizing HLA-DR, -DQ, and class I antigens supported these observations. Enhancement of HLA class II gene expression by ras genes may have important implications for regulation of the immune system in response to transformation.