DNA methylation-mediated silencing of nonsteroidal anti-inflammatory drug-activated gene (NAG-1/GDF15) in glioma cell lines

✍ Scribed by Mitsutoshi Kadowaki; Hiroki Yoshioka; Hideki Kamitani; Takashi Watanabe; Paul A. Wade; Thomas E. Eling

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: French
• Weight: 757 KB
• Volume: 130
• Category: Article
• ISSN: 0020-7136
• DOI: 10.1002/ijc.26082

✦ Synopsis

Abstract

Nonsteroidal anti‐inflammatory drug‐activated gene, NAG‐1, a transforming growth factor‐β member, is involved in tumor progression and development. The association between NAG‐1 expression and development and progression of glioma has not been well defined. Glioblastoma cell lines have lower basal expression of NAG‐1 than other gliomas and normal astrocytes. Most primary human gliomas have very low levels of NAG‐1 expression. NAG‐1 basal expression appeared to inversely correlate with tumor grade in glioma. Aberrant promoter hypermethylation is a common mechanism for silencing of tumor suppressor genes in cancer cells. In glioblastoma cell lines, NAG‐1 expression was increased by the demethylating agent, 5‐aza‐2′‐deoxycytidine. To investigate whether the NAG‐1 gene was silenced by hypermethylation in glioblastoma, we examined DNA methylation status using genomic bisulfite sequencing. The NAG‐1 promoter was densely methylated in several glioblastoma cell lines as well as in primary oligodendroglioma tumor samples, which have low basal expression of NAG‐1. DNA methylation at two specific sites (−53 and +55 CpG sites) in the NAG‐1 promoter was strongly associated with low NAG‐1 expression. The methylation of the NAG‐1 promoter at the −53 site blocks Egr‐1 binding and thereby suppresses Nag‐1 induction. Treatment of cells with low basal NAG‐1 expression with NAG‐1 inducer also did not increase NAG‐1. Incubation with a demethylation chemical increased Nag‐1 basal expression and subsequent incubation with a NAG‐1 inducer increased NAG‐1 expression. We concluded from these data that methylation of specific promoter sequences causes transcriptional silencing of the NAG‐1 locus in glioma and may ultimately contribute to tumor progression.