MUC1 induces drug resistance in pancreatic cancer cells via upregulation of multidrug resistance genes.

MUC1 (CD227), a membrane tethered mucin glycoprotein, is overexpressed in >60% of human pancreatic cancers (PCs), and is associated with poor prognosis, enhanced metastasis and chemoresistance. The objective of this study was to delineate the mechanism by which MUC1 induces drug resistance in human (BxPC3 and Capan-1) and mouse (KCKO, KCM) PC cells. We report that PC cells that express high levels of MUC1 exhibit increased resistance to chemotherapeutic drugs (gemcitabine and etoposide) in comparison with cells that express low levels of MUC1. This chemo resistance was attributed to the enhanced expression of multidrug resistance (MDR) genes including ABCC1, ABCC3, ABCC5 and ABCB1. In particular, levels of MRP1 protein encoded by the ABCC1 gene were significantly higher in the MUC1-high PC cells. In BxPC3 and Capan-1 cells MUC1 upregulates MRP1 via an Akt-dependent pathway, whereas in KCM cells MUC1-mediated MRP1 upregulation is via an Akt-independent mechanism. In KCM, BxPC3 and Capan-1 cells, the cytoplasmic tail motif of MUC1 associates directly with the promoter region of the Abcc1/ABCC1 gene, indicating a possible role of MUC1 acting as a transcriptional regulator of this gene. This is the first report to show that MUC1 can directly regulate the expression of MDR genes in PC cells, and thus confer drug resistance.