DNA methylation-dependent regulation of human CD99 expression in Hodgkin and Reed-Sternberg cells of Hodgkin's lymphoma

摘要

Human CD99 is an integral transmembrane protein, which was recently suggested as a potential tumor suppressor in the certain types of tumors. It has been previously shown that CD99 is underexpressed in malignant Hodgkin and Reed-Sternberg (H-RS) cells of Hodgkin's lymphoma (HL). In this study, to investigate the mechanism by which the downregulation of CD99 molecules in H-RS cells takes place, the expression and gene methylation of human CD99 were analyzed in an H-RS cell line, L428. First, CD99 mRNA and protein expression of the cells were analyzed using RT-PCR and Western analysis. In addition, methylation profile of the CD99 promoter region was analyzed using methylation specific PCR (MSP) and subsequent DNA sequencing. In LA28, the CD99 mRNA level as well as the protein level was substantially lower than those in a corresponding normal cell line. MSP analysis of the CD99 promoter region of the L428 cells, revealed the high incidence of methylated CpG dinucleotides in the CD99 promoter. Furthermore, demethylation by the treatment of 5'-azacytidine induced CD99 expression in the L428 cells, indicating a critical role of methylation in CD99 gene silencing in H-PS cells. Taken together, these results indicate that the downregulation of CD99 in malignant H-RS cells is, at least in part, associated with methylation of the gene, suggesting a potential link between the gene hypermethylation and HL pathogenesis.