Locus-specific regulation of Kd, Dd, and Ld class I genes in the BALB/c S49 lymphoma sublines

The S49 tumor sublines are variants isolated from a single parent BALB/c tumor which demonstrate locus-specific shut-off of their Kd, Dd, and/or Ld surface molecules. Four phenotypically different sublines were characterized: wild-type (Kd Dd Ld)+, a null phenotype (Kd Dd Ld)-, and two intermediates (Kd Dd)+ (Ld)- and (Kd)+ (Dd, Ld)-. Nonexpressed class I Ag were not induced with IFN-gamma even though the expressed antigens were found to be appropriately responsive. Southern blot analysis using probes specific for the 5', exonic or 3' portions of the Kd, Dd, and Ld genes indicated that these S49 sublines have no major chromosomal aberrancies. Northern blot analysis of RNA from each S49 subline using locus-specific oligonucleotide probes revealed message only for the expressed Ag. Thus, the locus-specific shut-off of class I expression in these tumors appears to be acting at the transcriptional level. RNase protection analysis confirmed this result and furthermore demonstrated that the repression is exquisitely specific for the Kd, Dd, and Ld genes as other "class I-like" messages were detected in each cell line. These findings are discussed in the context of the various cis- and trans-acting mechanisms that have been proposed to regulate class I expression.