Differential expression of MHC class II genes in lung tumour cell lines

Molecular characterization of HLA class II expression was investigated in f ive lung tumour cell lines at the protein and mRNA levels. The cell lines e xhibited a differential expression of HLA-DR, HLA-DP and HLA-DQ products an d also showed differences in the inducibility of HLA class II genes by gamm a-IFN. Gamma-IFN stimulation induced only HLA-DR expression to varying degr ees in three cell lines, while only one cell line showed stimulation for HL A-DP and none for HLA-DQ antigens. These results suggest locus-specific reg ulation for the three loci. The presence of DR protein on the cell-surface membrane was always positively correlated with the presence of HLA-DR mRNA in the cells. After treatment with 5-azacytidine in the A549 cell line, whi ch expressed the lowest values, there was no effect on HLA class II levels. This suggested that methylation does not play an important role in the lac k of MHC class II antigen expression. In addition to studying mRNA levels of HLA class II antigens, we analysed m RNA of the proto-oncogene myc and observed a positive correlation of two mR NA: the increments in HLA-DR expression were associated with increments in c-myc expression. This suggests a relationship between the regulatory mecha nisms which control the expression of c-myc and HLA-DR antigens in lung tum our cell lines.