Evaluation of Nrf2 signaling pathway in biopsy specimens of patients with colorectal cancer

Abstract

Abstract Background: Colorectal cancer (CRC) is the fourth leading cause of cancer−related death worldwide. Activation of ABCB1 gene and its main product, P−glycoprotein, is the common reason for chemoresistance. The nuclear factor–- erythroid 2–related factor2 (Nrf2) is directly regulated by Kelch like ECH–associated protein1 (Keap1). In addition, Nrf2 is a key transcriptional factor that regulates efflux transporters, including P−gp. The aim of this study was to investigate the expression levels of Nrf2, Keap1 and ABCB1 in the biopsy samples and their association with clinicopathological features in CRC patients. Methods: Both mRNA and protein expression levels were measured by Real−time PCR and immunohistochemistry (IHC), respectively, in biopsies from colonoscopy in 65 CRC patients compared to those in 65 non−CRC individuals. Results: While expression levels of Nrf2 and ABCB1 (P−gp) were markedly higher in both mRNA and protein levels in CRC biopsies (p < 0.01), Keap1 expression level was significantly lower in these samples (p < 0.05). Positive correlations between Nrf2 expression level and tumor size (p = 0.003), lymph node (p = 0.038), distant metastasis (p = 0.008), and smoking status (p = 0.02) were observed. However, P–gp expression was associated only with patient age and smoking status. In addition, there was a positive correlation between protein levels of Nrf2 and P−gp, in both CRC (r = 0.617, p < 0.001) and non−CRC tissues (r = 0.930, p < 0.001). Conclusion: In conclusion, over-expression of Nrf2 and ABCB1/P−gp, as well as down-regulation of mRNA expression level of Keap1 in CRC patients denotes the role of Keap1/Nrf2/ABCB1 axis in CRC progression and chemoresistance. Our data suggest that therapeutic inhibition of Nrf2/ABCB1 signaling can be considered as a novel strategy to improve the efficacy of chemotherapeutics against CRC. Keywords: ABCB1/P−gp Chemotherapy Clinicopathological criteria Colorectal cancer Keap1 Nrf2