Epigenetic regulation of RhoB loss of expression in lung cancer

Julien Mazières,Daniel Tovar,Claire Marty-Detraves,Biao He,Anne Pradines,David Jablons,Jacobo Nieto-Acosta,Carine Clanet,Gilles Favre

doi:10.1186/1471-2407-7-220

Abstract

BackgroundRhoB is down-regulated in most lung cancer cell lines and tumor tissues when compared with their normal counterparts. The mechanism of this loss of expression is not yet deciphered.MethodsSince no mutation has been reported in the RhoB sequence, we investigated the epigenetic regulation of RhoB expression by analyzing the effect of HDAC inhibitors and methyltransferase inhibitors, by direct sequencing after bisulfite treatment and by methylation specific PCR.ResultsWe first showed that histone deacetylase (HDAC) inhibitors induce a significant RhoB re-expression in lung cancer cell lines whereas only a slight effect was observed with methyl transferase inhibitors. As promoter methylation is the most common epigenetic process in lung cancer, we performed methylation specific PCR and sequence analysis after bisulfite treatment and demonstrated that RhoB was methylated neither in lung cancer cell lines nor in tumor tissues. We also showed that a variable number of tandem repeats sequences in the 5' region of the RhoB gene was involved in HDAC response.ConclusionWe thus propose that RhoB regulation of expression occurs mainly by histone deacetylation rather than by promoter hypermethylation and that this process can be modulated by specific 5' sequences within the promoter.

Highlights

RhoB is down-regulated in most lung cancer cell lines and tumor tissues when compared with their normal counterparts
We recently showed that RhoB loss of expression occurred frequently in lung carcinogenesis [1]
We previously reported the presence of a Variable Number of Tandem Repeat (VNTR) sequence in the human RhoB 5' region that is known to be linked with the penetrance and the development of several cancers [18]

Summary

Introduction

RhoB is down-regulated in most lung cancer cell lines and tumor tissues when compared with their normal counterparts. The mechanism of this loss of expression is not yet deciphered. RhoB has been recently identified as a gene widely involved in lung carcinogenesis [1,2,3]. We recently showed that RhoB loss of expression occurred frequently in lung carcinogenesis [1]. We showed in two independent immunohistochemical studies that RhoB protein was expressed in normal lung and decreased dramatically through lung cancer progression. We showed that ectopic expression of RhoB in lung cancer cell line A549 suppressed cell proliferation, anchorage-independent growth, and xenograft tumor growth in nude mice [1]. Loss of expression of RhoB has been reported in other solid tumors such as Head and Neck carcinomas [15] and brain tumors [16]

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Conclusion