Differential expression of insulin receptor isoforms A and B in highly proliferative stem and tumor cells vs. differentiated intestinal epithelial cells

Abstract

Little is known about expression and roles of insulin receptor (IR) in the intestinal epithelium despite emerging links between obesity, hyperinsulinemia, and intestinal dysfunction or cancer risk. IR exists as an IR‐B isoform that mediates insulin's metabolic actions and an IR‐A isoform implicated in fetal growth and recently, cancer. This study used Sox9‐EGFP reporter mice, ApcMin/+ mice, and human colorectal cancer cell lines (CRC) to test the hypothesis that IR‐A and IR‐B have distinct expression profiles in highly proliferative vs differentiated normal intestinal epithelial cells (IEC) or CRC.ResultsIR‐A predominates in highly proliferative intestinal epithelial stem cells and progenitors, while IR‐B predominates in differentiated lineages. In ApcMin/+ mice, the IR‐B:IR‐A ratio is dramatically decreased in tumor vs non‐tumor tissue in small intestine (0.65 ± 0.02 vs 1.3 ± 0.03) and colon (0.63 ± 0.1 vs 1.27 ± 0.9). The IR‐B:IR‐A ratio is higher in CRC with the ability to differentiate vs undifferentiated, aggressively growing CRC. The ratio of IR‐B:IR‐A is significantly increased in differentiated vs undifferentiated Caco2 cells (2.2 ± 0.2 vs 1.5 ± 0.1). We conclude that relative expression levels of IR‐B:IR‐A may be critical determinants of normal IEC or CRC differentiation. Grants: F31AG040943 (SFB) and NIH DK040247‐19 (PKL).