Epigenetic Silencing of the RASSF1A Tumor Suppressor Gene through HOXB3-Mediated Induction of DNMT3B Expression

Abstract

SUMMARY The RASSF1A tumor suppressor gene is epigenetically silenced in a variety of cancers. Here we perform a genome-wide human shRNA screen and find that epigenetic silencing of RASSF1A requires the homeobox protein HOXB3. We show that HOXB3 binds to the DNA methyltransferase DNMT3B gene and increases its expression. DNMT3B, in turn, is recruited to the RASSF1A promoter, resulting in hypermethylation and silencing of RASSF1A expression. DNMT3B recruitment is facilitated through interactions with Polycomb repressor complex 2 and MYC, which is bound to the RASSF1A promoter. Mouse xenograft experiments indicate that the oncogenic activity of HOXB3 is due, at least in part, to epigenetic silencing of RASSF1A. Expression analysis in human lung adenocarcinoma samples reveals that RASSF1A silencing strongly correlates with over-expression of HOXB3 and DNMT3B. Analysis of human cancer cell lines indicates that the RASSF1A epigenetic silencing mechanism described here may be common in diverse cancer types.

Targeted Methylation of Two Tumor Suppressor Genes Is Sufficient to Transform Mesenchymal Stem Cells into Cancer Stem/Initiating Cells

“…3B). On the basis of the wide range of cellular functions associated with HIC1 and RassF1A (16,19,24), it was not surprising to observe global changes in the MSC methylome. Furthermore, as both HIC1 and RassF1A were reported to function as TSGs that act via p53, we conducted unsupervised ontological analysis of the array target loci and found that p53 and its associated signaling components were significantly altered by me_H&R transfection (Fig.…”

DNA Methylation and Nonsmall Cell Lung Cancer

“…RASSF1A promoter is frequently hypermethylated in a variety of cancers, including lung carcinoma (Dammann et al, 2000(Dammann et al, , 2001(Dammann et al, , 2005Honorio et al, 2001), and its hypermethylation leads to epigenetic silencing of RASSF1A by HOXB3-mediated induction of DNMT3B expression (Palakurthy et al, 2009). APC is a negative regulator of Wingless-INT (WNT) pathway, which involves in selfrenewal of stem cell (Mazieres et al, 2005), and APC methylation occurrence rate is up to 94% in NSCLC but 20% in normal control group (Brabender et al, 2001).…”

The DNMT3B -579 G>T promoter polymorphism and risk of lung cancer

“…-579 G>T is a single SNP in the promoter region of the DNMT3B gene, which may modify susceptibility to tumors (18,19). DNMT3Bs are the predominant expression forms of DNMT3B in human lung cancer and, in part, are involved in the epigenetic silencing of RASSF1A (20). DNMT3B proteins were highly expressed in a coordinate manner in lung tumors, particularly in smokers, and overexpression may result in promoter hypermethylation of multiple tumor suppressor genes (TSGs), ultimately leading to lung tumorigenesis and poor prognosis (21).…”