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.