Inactivation of p16 by methylation in human lung adenocarcinoma

Abstract

Adenocarcinoma (AdC) of the central and peripheral lung may arise through distinct molecular mechanisms resulting from differences in exposure of these lung compartments to carcinogen. Inactivation of the p16 gene by aberrant promoter hypermethylation, an epigenetic mechanism, has been implicated in AdC development associated with tobacco. We investigated the frequency of p16 methylation in AdC from three different populations: smokers, former uranium miners who smoked, and those who had never smoked (NS). We also examined the effect of central versus peripheral tumor location on gene inactivation. We found that p16 was methylated in 53% (36/68), 59% (16/27), and 49% (27/55) of peripheral tumors from smokers, former uranium miners, and those in the NS group. Central AdCs seem to have a higher frequency of p16 methylation (21/30; 70%) than peripheral tumors. This higher frequency of p16 methylation in central AdCs parallels our findings for squamous carcinoma, a predominantly central lesion. These studies also indicate that radon exposure does not interact synergistically with tobacco to target this gene for inactivation, but they do implicate p16 as a major pathway for AdC development in the NS group. The interaction of p19 with p16 methylation will also be discussed.