The Loss/Decreased Expression of GPR43 in Colorectal Carcinogenesis: A Highly Possible Tumor Suppressor Gene and Novel Therapeutic Target
KA Matkowskyj, J Liao, H Li, SM Rao, G-Y Yang. Northwestern University, Chicago, IL
Background: Short chain fatty acids (SCFAs) are an essential fuel source for colonocytes and are important for the functional integrity of the epithelium. The effects of SCFAs on cancer cell differentiation have been extensively studied. SCFAs can activate 2 closely related G protein-coupled receptors, GPR41 and GPR43. The role of GPR receptors, particularly in colon carcinogenesis, are unknown. The aim of this study is to analyze GPR43 expression in normal colonic epithelium, tubular adenomas, primary and metastatic colonic adenocarcinomas and to explore its potential role in carcinogenesis.
Design: Four tissue microarrays were created. Three of these arrays included 15 cases from colonic resection specimens with normal, primary and metastatic colonic adenocarcinoma in either lymph nodes or liver from each patient. The last microarray contained 10 colonic specimens with 5 tubular adenomas (TA) and 5 adenocarcinomas arising in TA. Immunohistochemistry was performed using a polyclonal rabbit GPR43 antibody and the avidin-biotin-peroxidase approach. The staining intensity was classified as no staining, low intensity staining, or high intensity staining. Next, protein was extracted from 11 colonic cells lines including the normal human colonic epithelial cell line NCM460 and the colonic adenocarcinoma cell line HT29, followed by western blotting using GPR43 antibody.
Results: High intensity expression for GPR43 was identified as punctuate, cytoplasmic staining in 100% of normal colonic epithelium (n=15). Loss of expression was found in 65% (13/20) of adenocarcinomas; specifically, all moderately and poorly differentiated carcinomas showed no expression (n=13), compared to 100% (7/7) of well-differentiated carcinomas which showed identical levels of GPR43 expression as seen in normal colonic mucosa (p<0.01). Interestingly, metastatic adenocarcinoma showed a 93% loss of expression for GPR43 (n=15) regardless of differentiation status. All tubular adenomas (n=5) demonstrated identical levels of GPR43 expression as in normal mucosa. Western blot revealed high intensity expression of GPR43 in the NCM460 cell line and in only 1 of the 10 adenocarcinoma cell lines (HT29).
Conclusions: This study demonstrates a significant decrease/loss of GPR43 receptor expression in moderate/poorly differentiated colonic adenocarcinomas and associated metastatic lesions, indicating it may serve as a useful malignant biomarker. Further studies are warranted exploring this possible tumor suppressor gene in colonic adenocarcinoma.
Tuesday, March 23, 2010 1:00 PM
Poster Session IV # 78, Tuesday Afternoon