Objective: To investigate the effect of 5-azacytidine on XAF1 expression in myeloma cell lines RPMI8226 and XG-7 and the in vitro anti-myeloma activity of 5-azacytidine.
Methods: XAF1 mRNA and protein expression was detected by semi-quantitative reverse transcriptase PCR and Western blot, respectively. Methylation specific PCR (MSP) was used to detect methylation status of XAF1 promoter CpG islands. RPMI8226 and XG-7 cells were treated with 0-5 micromol/L of 5-azacytidine and Cell Counting Kit-8 colorimetric assay was used to evaluate the growth inhibitory effect. Cell apoptosis was determined with Annexin V-PE/7-AAD staining by flow cytometry.
Results: Untreated RPMI8226 cells expressed XAF1 mRNA isoforms 1 and 2, and untreated XG-7 cells had no XAF1 expression. Hypermethylation of XAF1 promoter CpG islands was detected in both the cell lines. After treated with 2.5 micromol/L 5-azacytidine for 72 h, both the cell lines expressed full-length XAF1 transcript and protein. 5-azacytidine treatment led to XAF1 promoter CpG islands hypomethylation and showed anti-myeloma activity in a time- and concentration-dependent manner with IC50 of 2.4 micromol/L and 2.6 micromol/L at 48 h for RPMI8226 and XG-7 cell lines, respectively.
Conclusions: Lack of XAF1 expression and abnormal expression of XAF1 in myeloma cell lines are associated with XAF1 gene promoter CpG islands hypermethylation. 5-azacytidine treatment can induce XAF1 mRNA and protein expression and exerts anti-myeloma activity via apoptosis at clinically achievable concentrations.