Journal Article

Increase of carcinogenic risk via enhancement of cyclooxygenase-2 expression and hydroxyestradiol accumulation in human lung cells as a result of interaction between BaP and 17-beta estradiol

Louis W. Chang, Yun-Ching Chang, Chia-Chi Ho, Ming-Hsien Tsai and Pinpin Lin

in Carcinogenesis

Volume 28, issue 7, pages 1606-1612
Published in print July 2007 | ISSN: 0143-3334
Published online February 2007 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgm013
Increase of carcinogenic risk via enhancement of cyclooxygenase-2 expression and hydroxyestradiol accumulation in human lung cells as a result of interaction between BaP and 17-beta estradiol

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Animal studies demonstrated that females are more susceptible than males to benzo[a]pyrene (BaP)-induced toxicities, including lung carcinogenesis. Elevation of cyclooxygenase-2 (COX-2) expression has been shown to increase the risk of cancer development. BaP induces COX-2 expression, and an interaction between BaP and estrogen in relation to COX-2 expression is suspected. In the present study, 10 μM BaP alone only slightly increased COX-2 mRNA expression and 10 nM 17-beta estradiol (E2) alone slightly increased prostaglandin E2 (PGE2) secretion in human bronchial epithelial cells. However, co-treatment with BaP and E2 potentiated COX-2 mRNA expression and significantly elevated PGE2 secretion. Utilizing specific inhibitors and reporter assays, we further investigated the potentiation mechanisms of E2 on BaP-induced COX-2 expression. First, E2 activated estrogen receptor to increase PGE2 secretion, which directly increased COX-2 expression. Second, E2 potentiated BaP-induced nuclear factor-κB (NF-κB) activation, which regulates COX-2 expression. Third, although the aryl hydrocarbon receptor (AhR) did not play a role in BaP-induced COX-2 expression, the potentiation effect of E2 itself was AhR dependent. We further demonstrated that BaP induced the production of genotoxic E2 metabolites (2- and 4-hydroxyestradiols) via AhR-up-regulated cytochromes P450 1A1 and 1B1. These metabolites could directly activate NF-κB to further promote COX-2 mRNA expression in human lung epithelial cells. These findings were further supported by increased PGE2 secretion in rat lung slice cultures. Our findings that the BaP–E2 interaction enhanced COX-2 expression and hydroxyestradiol accumulation in the media of cultivated lung cells and tissues provide the needed scientific basis for higher risk of BaP-associated lung cancer in females.

Journal Article.  5305 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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