Aims: We have shown earlier that inhibition of aldose reductase (AR), an oxidative stress-response protein, prevents colon cancer cell growth in vitro and in vivo. Changes in microribonucleic acid (miR) expression can contribute to cancer by modulating the functional expression of critical genes involved in cancer growth and metastasis. However, the molecular mechanisms by which AR regulates miR expression and their dependent mitogenic effects in cancer cells are not known. Therefore, we investigated how AR regulates growth factor-induced expression of miRs and growth of colon cancer cells.
Results: Inhibition of AR significantly downregulated growth factor-induced miR-21 expression in human colon cancer cells, HT29, SW480, and Caco-2. Further, AR inhibition also increased phosphatase and tensin homolog (PTEN) (a direct target of miR-21) and forkhead box O3A (FOXO3a) in colon cancer cells. Our results obtained with HT29 cells ablated with FOXO3a siRNA showed increased activator protein-1 (AP-1) activation and miR-21 expression, indicating that FOXO3a represses miR-21 via AP-1 inactivation. Inhibition of AR also prevented the epidermal growth factor-induced phosphorylation of phosphatidylinositol 3-kinase (PI3K), serine/threonine kinase (AKT), c-Jun, c-Fos, PTEN, and FOXO3a, and deoxyribonucleic acid (DNA)-binding activity of AP-1. More importantly, in human colon adenocarcinoma xenograft tissues, miR-21 expression was lower, and PTEN and FOXO3a levels were significantly higher in AR inhibitor-treated mice compared to controls.
Innovation: These findings demonstrate a novel role of AR in the regulation of miR-21 and its target PTEN in growth factor-induced colon cancer cell growth.
Conclusions: Collectively, these results show a novel role of AR in mediation of growth factor-induced colon cancer growth by modulating miR-21, PTEN, and FOXO3a expression through reactive oxygen species (ROS)/PI3K/AKT/AP-1.