Progesterone Receptor Upregulation is an Early Event in Colon Carcinogenesis: Potential Modulator of Neoplastic Risk in Women

Abstract

Purpose: While colorectal cancer (CRC) impacts upon the genders equally, there are profound differences in biology and epidemiology (e.g., women tend to have proximal lesions, MSI high tumors etc). However, clinical practice largely treats CRC as gender-neutral. Our group has shown that CRC biomarkers are different in women thus having significant implications for screening (JAMA 2009, Can Prev Res 2010). The gender differences are generally attributed to sex steroids although precise hormones remain unclear. For instance, WHI data indicates estrogen/progesterone reduced CRC by 38% (Chlebowski et al., NEJM 2004) although estrogen alone had no effect (OR:1.08, Anderson et al., JAMA 2004) suggesting that the progesterone receptor (PR) was important. However, the role of PR in CRC remains unexplored. Methods: For these studies we employed the azoxymethane (AOM)-treated rat which is the best-accepted model of experimental colon carcinogenesis requiring 20 and 40 weeks for adenomas and CRCs to develop, respectively. PR expression from colonic mucosa was assessed by real time RT-PCR using high capacity cDNA synthesis kit and PR-specific taqman probe. In order to further assess PR's role, we employed a well-established chemopreventive agent, celecoxib in the human CRC cell line HCT 116. (Bertagnolli et al., NEJM 2006). We evaluated protein levels using quantitative immunoblot analysis. Results: In the AOM-treated rat, PR was markedly (319.6±12.2%) increased in the tumor when compared to colonic mucosal scrapings from age-matched saline-treated controls. Moreover, a comparable (392±4.2%, p<0.001) increase was noted in the microscopically-normal mucosa of these AOM-treated rats implicating field carcinogenesis. Typically, we examined the 10 week (premalignant) time-point since it best replicates human field carcinogenesis and noted a comparable induction of PR in the premalignant mucosa (313±4.2%, p<0.001). From a diagnostic perspective, the AUROC at the 10 week timepoint for discriminating AOM versus control rats was an impressive 0.97. Finally, we noticed that PR was markedly altered with celecoxib treatment (50μm) in HCT116 by 37.4% (p<0.01). Conclusion: We report, herein, for the first time that PR induction is an early event in colorectal carcinogenesis. Moreover, its reversal by chemoprevention underscores PR's biological significance. Importantly, the performance of PR expression was outstandingly supporting a possible role in CRC screening, potentially coupled with our recently developed ability to perform real time PCR on mucus layer fecal colonocytes (to detect field carcinogenesis). Furthermore, PR status may finally explain some of the gender-related differences in colon carcinogenesis.