Global DNA hypomethylation-induced ΔNp73 transcriptional activation in non-small cell lung cancer

p73 possesses an extrinsic P1 promoter and an intrinsic P2 promoter controlling the expression of the pro-apoptotic TAp73 isoforms and the anti-apoptotic ΔΝp73 isoforms respectively. In this study, we investigated the DNA methylation status of both promoters as a means of epigenetic transcriptional control of their corresponding isoforms in 102 primary non-small cell lung carcinomas (NSCLCs). We demonstrated that while P1 hypermethylation-associated reduction of TAp73 mRNA levels is relatively infrequent, the P2 hypomethylation-associated over-expression of ΔΝp73 mRNA is a frequent event, particularly among squamous cell carcinomas. P2 hypomethylation strongly correlated with LINE-1 element hypomethylation, indicating that ΔΝp73 over-expression may be a passive consequence of global DNA hypomethylation.