Abstract LB-348: Chemoresistance in pancreatic cancer is conferred by MUC1 cytoplasmic tail binding to the promoter region of the ABCC1 (MRP-1) gene

Abstract

Abstract Introduction: The high mortality rate of pancreatic cancer (PC) is in part, due to their high propensity for metastasis and multidrug resistance. The three most common ways by which cancer cells acquire chemoresistance is via deregulation of apoptotic pathways, upregulation of survival pathways and upregulation of multi-drug resistance (MDR) genes. The MDR genes encode for ATP-binding cassette (ABC) membrane transporters, which extrudes chemotherapeutic drugs from cancer cells. However, the mechanisms behind the up-regulation of the MDR genes are not entirely understood. More than 90% of metastatic PC patients overexpress MUC1 (CD227), a membrane tethered mucin glycoprotein that has been linked to increased metastatic phenotype and drug resistance. The cytoplasmic tail (CT) of MUC1 has seven conserved tyrosine residues which are important for the signal transduction role of MUC1. The aim of this study was to understand the underlying mechanism by which MUC1 induces drug resistance in PC cells. Method: We used a panel of PC cells lines that endogenously express low or high levels of MUC1. The cells lines expressing low endogenous MUC1 were stably infected with the retroviral vector containing empty plasmid (Neo), or plasmid carrying full-length MUC1 (MUC1 WT), or full length MUC1 with the tyrosine residues of MUC1 CT mutated to phenylalanine (MUC1 Y0). The cells were treated with three commonly used chemotherapeutic/preventive drugs (Gemcitabine, Etoposide and Celecoxib). The level of dead cells was evaluated by H3 incorporation assay and Annexin V staining. We also checked for the activation of prosurvival pathways Erk1/2 and PI3K by Western Blot. The mRNA level of MDR genes were determined by RTPCR. CHIP (Chromatin Immunoprecipitation) was performed to determine the localization of MUC1 CT to the promoter region of ABCC1 gene (MRP1). Results: Our results indicate that PC cells expressing MUC1 WT or MUC1 Y0 have intrinsic resistance to chemotherapeutic, compared to cells expressing low levels of MUC1. We observed an enhanced activation of the prosurvival pathways Erk1/2 and PI3K in MUC1 high PC cells, compared to cells expressing low MUC1 or MUC1 Y0. Upon inhibition of the PI3K/Akt pathway, a partial loss in the chemoresistance was seen, indicating that this pathway is partially responsible for the chemoresistance. DNA microarray and RT PCR showed that the expression of MDR genes (ABCC1, ABCC3, ABCC5 and ABCB1) was significantly higher in PC cells expressing MUC1 WT or MUC1 Y0. Most importantly, for the first time, we showed that MUC1 CT localizes to the promoter region of a MDR gene, ABCC1. This suggests that MUC1 directly drives the transcription and expression of ABCC1 gene. The implications of the data are clinically significant as small molecule inhibitors can be designed to specifically block MUC1 CT signaling and transcriptional activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-348. doi:1538-7445.AM2012-LB-348