Comparison of the transcriptional regulation of classical and non-classical MHC class II genes.

The class II transactivator (CIITA) regulates expression of the classical and non-classical MHC class II genes, HLA-DR, -DP, -DQ and -DM, but not the B cell-specific HLA-DO (DO). Here we show that only HLA-DR expression is completely dependent on CIITA, since residual expression of HLA-DM, -DP and the beta chain of DQ was observed in CIITA-deficient RJ2.2.5 cells. Although DO shows a unique expression pattern compared to other MHC class II genes, prolonged IFN-gamma treatment of HeLa cells induced DOB expression. Similar to all MHC class II promoters, the DOB promoter contains the highly conserved W, X1, and Y boxes in addition to a putative OCT box. Mutational analysis of the DOB promoter demonstrated that the X1, Y and OCT boxes are necessary for maximum promoter activity.Furthermore, our results demonstrate that CREB-1, RFXANK and Oct-2 occupy the DOB promoter in vivo, However, CIITA and Bob-1 were only minimally recruited. Finally, fusion of Bjab, a DOB-negative B cell line, with.174 B cells that lack the complete MHC class II region (including the DO genes), lead to DO expression. These data indicate that the expression of DO is regulated by an unidentified factor in B cells.