Journal Article

Carcinogen exposure differentially modulates RAR-β promoter hypermethylation, an early and frequent event in mouse lung carcinogenesis

Brian R. Vuillemenot, Leah C. Pulling, William A. Palmisano, Julie A. Hutt and Steven A. Belinsky

in Carcinogenesis

Volume 25, issue 4, pages 623-629
Published in print April 2004 | ISSN: 0143-3334
Published online April 2004 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgh038
Carcinogen exposure differentially modulates RAR-β promoter hypermethylation, an early and frequent event in mouse lung carcinogenesis

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The retinoic acid receptor beta (RAR-β) gene encodes one of the primary receptors for retinoic acid, an important signaling molecule in lung growth, differentiation and carcinogenesis. RAR-β has been shown to be down-regulated by methylation in human lung cancer. We have used previously lung tumors induced in mice to evaluate the timing and effect of specific carcinogen exposures on targeting genes altered in human lung cancer. These studies were extended to characterize the role of methylation of the RAR-β gene in murine lung cancers. After treatment with the demethylating agent 5-aza-2′-deoxycytidine (DAC), RAR-β was re-expressed in silenced cell lines or expressed at a higher rate than without DAC, supporting methylation as the inactivating mechanism. Bisulfite sequencing detected dense methylation in the area of the CpG island that contained the 5′ untranslated region and the first translated exon in non-expressing cell lines, compared with minimal and heterogeneous methylation in normal mouse lung. Methylation-specific PCR revealed that this gene is targeted differentially by carcinogen exposures with the detection of methylated alleles in virtually all primary tumors associated with cigarette smoke or 4-methylnitrosamino-1-(3-pyridyl)-butanone (NNK) in contrast to half of tumors induced by methylene chloride or vinyl carbamate. RAR-β methylation was also detected in 54% of preneoplastic hyperplasias induced by treatment with NNK. Bisulfite sequencing of both premalignant and malignant lesions detected dense methylation in the same area observed in cell lines, substantiating that this gene is functionally inactivated at the earliest histologic stage of adenocarcinoma development. These studies demonstrate that aberrant methylation of RAR-β is an early and common alteration in murine lung tumors induced by several environmentally relevant exposures.

Keywords: DAC, 5-aza-2′-deoxycytidine; ER, estrogen receptor-α; MSP, methylation-specific PCR; NNK, 4-methylnitrosamino-1-(3-pyridyl)-butanone; RARE, retinoic acid response elements; RAR-β, retinoic acid receptor-β

Journal Article.  5310 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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