apoptosis; bone-marrow microenvironment; cancer; cyclin-dependent kinase inhibitor; DNA methylation; dna methyltransferase; gene-expression; histone deacetylase inhibitors; interleukin-6; methylation; molecular pathogenesis; multiple myeloma cell lines; multiple-myeloma; p16

Gene inactivation of the cyclin-dependent kinase inhibitors p16(INK4a), p15(INK4b) and p21(WAF) is frequently mediated by promoter gene methylation, whereas histone deacetylases (HDACs) control gene expression through their ability to deacetylate proteins. The effect of suberohydroxamic acid (SBHA) and 5-Aza-2 '-deoxycytidine (Decitabine) (DAC) treatments on the transcription of CDKN2A, CDKN2B and CDKN1A genes, and their effects on molecular biological behavior were examined in two myeloma cell lines, RPMI8226 and U266, which differ in p53-functionality and IL-6 expression. In both tested myeloma cell lines, a non-methylated state of the CDKN2B gene promoter region was detected with normal gene expression, and the same level of p15(INK4b) protein was detected by immunocytochemical staining. Furthermore, in myeloma cells treated with SBHA and DAC alone, the expression of both p15(INK4b) and p21(WAF) was significantly upregulated in RPMI8226 cells (p53-functional, without IL-6 expression), whereas in the U266 cell line (p53 deleted, expressing IL-6) only p21(WAF) expression was significantly increased. Moreover, the analysis revealed that treatment with DAC induced DNMT3B enhancement in U266 cells. In conclusion, in myeloma cells with IL-6 expression, significantly increased DNMT3B expression indicated the tumorigenic consequences of 5-Aza-2 ' deoxycytidine treatment, which requires careful use in diseases involving epigenetic dysregulation, such as multiple myeloma (MM).