UHRF1-Mediated Tumor Suppressor Gene Inactivation in Nonsmall Cell Lung Cancer

BACKGROUND: The UHRF7 gene possesses an essential role in DNA methylation maintenance, but its contribution to tumor suppressor gene hypermethylation in primary human cancers currently remains unclear. METHODS: mRNA expression levels of UHRF7, DNMT1, DNMT3A, DNMT3B, and E2F1 were evaluated in 105 primary nonsmall cell lung carcinomas by quantitative polymerase chain reaction. The methylation status of CDKN2A and RASSF1 promoters was examined by pyrosequencing. UHRF7 was knocked down by short hairpin RNA in A549 lung adenocarcinoma cells. RESULTS: All 4 genes were overexpressed in a coordinated manner in the lung tumor tissues, and their expression correlated with that of E2F1. Higher UHRF7 expression in tumor tissues correlated with the hypermethylation of CDKN2A (P=.005) and RASSF1 promoters (P=.034), and the relationship with a combined epigenotype was even stronger (P = 2.3 x 10(-4)). When UHRF7 was knocked down in A549 lung adenocarcinoma cells, lower methylation levels of RASSF1, CYGB, and CDH13 promoters were observed. Also, UHRF1 knockdown clones demonstrated reduced proliferation and decreased cell migration properties. CONCLUSIONS: Our data demonstrate that UHRF7 is a key epigenetic switch, which controls cell cycle in nonsmall cell lung carcinoma through its ability to sustain the transcriptional silencing of tumor suppressor genes by maintaining their promoters in a hypermethylated status. Thus, UHRF1 should be considered, along with DNMTs, among the potential targets for cancer treatment and/or therapeutic stratification. Cancer 2011;117:1027-37. (C) 2010 American Cancer Society.