Abstract 5748: Elevated aromatase, estrogen receptor variants and human hepatocellular carcinoma: a unifying hypothetical model

Abstract

Abstract Although there is evidence that hints at a potential role of estrogen in hepatocellular carcinoma (HCC), the use of antiestrogens has failed to improve disease-free and overall survival of HCC patients. In the present study we have investigated aromatase-driven estrogen formation in nontumoral and malignant human liver tissues and cells, also in relation to the expression of estrogen receptor (ER) β, ERα, and their splicing variants, aiming to get insights into the potential role of estrogens and the underlying mechanism(s) in human HCC. Chromatographic and exon-specific RT-PCR analyses were respectively used to assess activity and expression the aromatase enzyme and the expression of wild-type (hERα66, hERα1) and variant (hERα46, hERα36; hERα2/Cx, hERα5) ER, both in vivo and in vitro. Following incubation of tissue minces or liver cell lines, with either testosterone or androstenedione used as androgen labeled precursor, human HCC tissues and HepG2 hepatoma cells showed elevated aromatase activity, with estrogen formation rates of 20% at 24h and >95% at 72h. By contrast, no aromatase activity could be detected in nontumoral hepatic tissues and HA22T liver cancer. Cirrhotic samples exhibited variable enzyme activity, with average estrogen formation rates of 4-8%, while Huh7 HCC cells gave rise to 34% estrogen formation. Markedly lower aromatase mRNA levels were observed in HA22T cells and nontumoral liver tissues, as compared to HepG2 cells and HCC samples. Cirrhotic specimens displayed variable transcript levels, comparable in turn to those observed in nontumoral or HCC tissues. Interestingly, no or low expression of both wild type ERα and ERα could be detected in liver cancer cells and malignant tissues. Conversely, equivalent amounts of the hERα46 variant were observed in both cells and tissues, while hERα36 expression was highest in HepG2 cells and HCC samples, intermediate in Huh7 cells and cirrhotic tissues, and very low in HA22T cells and nontumoral liver. Only occasional expression of the two ERα variants was observed in liver cancer cells and tissues. It is noteworthy that the pattern of hERα36 expression was strictly related to that of the aromatase enzyme, suggesting that this ERα variant may be primarily implicated as a mediator of estrogen action in the malignant liver. Based on present and previous experimental evidence, we propose here a unifying hypothetical model whereby locally elevated, aromatase-driven, estrogen formation, combined with a shift in wild type/variant ER expression, may be primarily implicated in development and/or progression of human HCC and other neoplastic or chronic human diseases. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5748. doi:1538-7445.AM2012-5748