SPAN-Xb expression in myeloma cells is dependent on promoter hypomethylation and can be upregulated pharmacologically

Abstract

SPAN-Xb is a novel cancer-testis antigen in multiple myeloma (MM). In this study, we determined the mechanisms regulating SPAN-Xb expression in MM. SPAN-Xb promoter sequence was first cloned into the CAT-reporter vector to determine the role of promoter methylation in the regulation of gene expression. Tumor cells were treated with 5-azacytidine and a panel of cytokines were used to determine their ability to induce SPAN-Xb expression. Bisulfite conversion with sequence analysis was applied to a panel of tumor cells and normal tissues to correlate the CpG dinucleotide hypomethylation and SPAN-Xb expression. We found that SPAN-Xb promoter function could be silenced by methylation. 5-Azacytidine induced promoter hypomethylation and resulted in SPAN-Xb expression, at both the transcript and protein levels. Hypomethylation of the CpG dinucleotides at positions -310, -307, -299 and -221 within the SPAN-Xb promoter strongly predict for SPAN-Xb expression. Both IL-7 and GM-CSF were also able to upregulate the expression of SPAN-Xb in myeloma cells, but only after the promoter sequence has been hypomethylated. Our results provide the first evidence showing the role of promoter methylation in the primary regulation of SPAN-Xb and the ability of IL-7 and GM-CSF to further enhance SPAN-Xb gene and protein expression in myeloma cells.