Journal Article

A Novel Retinoic Acid Receptor β Isoform and Retinoid Resistance in Lung Carcinogenesis

W. Jeffrey Petty, Na Li, Adrian Biddle, Rebecca Bounds, Christopher Nitkin, Yan Ma, Konstantin H. Dragnev, Sarah J. Freemantle and Ethan Dmitrovsky

in JNCI: Journal of the National Cancer Institute

Volume 97, issue 22, pages 1645-1651
Published in print November 2005 | ISSN: 0027-8874
Published online November 2005 | e-ISSN: 1460-2105 | DOI: http://dx.doi.org/10.1093/jnci/dji371

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Background: We previously reported that all-trans-retinoic acid (RA) treatment can prevent in vitro transformation of immortalized human bronchial epithelial (HBE) cells. Methods: To determine whether methylation inhibits RARβ expression in HBE cells, we used sodium bisulfite sequencing to compare RARβ P2 promoter methylation patterns in RA-sensitive (BEAS-2B) and RA-resistant (BEAS-2B-R1) HBE cells. Immunoblotting was used to assess induction of the RARβ, placental transforming growth factor β (PTGF-β), Fos-related antigen 1 (Fra-1), and transglutaminase II (TGase II) proteins by RA following treatment with azacitidine, a DNA demethylating agent. The expression, transcriptional activity, and growth suppressive activity of RARβ1′, a novel RAR isoform, were evaluated in lung cancer cells transfected with RARβ1′, and expression was also studied in paired normal lung tissues and lung tumors. All statistical tests were two-sided. Results: Hypermethylation was observed in the 3′ region of the RARβ P2 promoter of BEAS-2B-R1 but not BEAS-2B cells. Azacitidine treatment of BEAS-2B-R1 cells restored RA-inducible RARβ2 and PTGF-β expression but not that of RARβ1′, Fra-1, or TGase II. RARβ1′ expression was repressed in RA-resistant BEAS-2B-R1 cells and in lung cancers, compared with adjacent normal lung tissues. BEAS-2B-R1 cells transiently transfected with RARβ1′ had increased RA-dependent activation of a retinoic acid receptor element (RARE)–containing reporter plasmid compared with vector control (mean = 3.2, 95% confidence interval [CI] = 3.1 to 3.3 versus mean = 1.4, 95% CI = 1.3 to 1.5; P<.001). In H358 lung cancer cells transiently transfected with RARβ1′, RA treatment restored target gene expression compared with that in vector-transfected cells and suppressed cell growth compared with that in untreated cells (4 μM; treated mean = 0.49 versus untreated mean = 1.0, difference = 0.51, 95% CI = 0.35 to 0.67, P = .003; 8 μM: treated mean = 0.50 versus untreated mean = 1.0, difference = 0.50, 95% CI = 0.26 to 0.74, P = .015). Conclusion: Restoration of RARβ1′ expression may overcome retinoid resistance in lung carcinogenesis.

Journal Article.  5616 words.  Illustrated.

Subjects: Medical Oncology

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