Abstract 508: Identification of FRA-1 as a potential driver of pro-invasive properties in pancreatic cancer in conjunction with MUC1

Abstract

The transmembrane mucin, MUC1, contributes to the progression of pancreatic cancer, in part by conducting signals from the cell surface that regulate expression of molecules associated with aggressive tumor behavior. We investigated transcriptional co-regulatory effects mediated by interactions of the MUC1 cytoplasmic tail with activator protein 1 (AP-1). Previous results suggest that MUC1 regulates the capacity of AP-1 to bind specific promoter elements and regulate genes that contribute to tumor progression. The DNA binding activity of AP-1 is controlled in several ways including composition of the protein dimer. The precise mechanism by which MUC1 alters transcriptional complexes remains unknown. We sought to determine how MUC1 influences the formation of AP-1 complexes and potential downstream effects.

We found MUC1 increased c-Jun protein levels, the major component of AP-1, in a manner largely independent of transcriptional upregulation (mRNA upregulation was observed in only one cell line of several analyzed). Formation of the AP-1 dimer was assessed by quantitative and semi-quantitative assays. MUC1 promoted the association of c-Jun with the Fos protein, FRA-1. This association was promoted by enhanced ERK2 signaling in MUC1 expressing cell lines. In breast cancer, FRA-1 drives an invasive and metastatic phenotype. Overexpression of FRA-1 in pancreatic cancer cell lines promoted migratory and invasive behaviors in vitro. Blocking FRA-1 activity by shRNA knockdown or ERK inhibition decreased migration and invasion. Analysis of gene expression in pancreatic tumor samples and normal, uninvolved tissue [mined from the Gene Expression Omnibus (GEO)] revealed that tumor samples had significantly increased levels of FRA-1 mRNA. A subset of these samples exhibited gene expression patterns consistent with a FRA-1:EMT phenotype previously observed in colorectal cancer cells. We evaluated expression of FRA-1 protein in primary pancreatic tumors, liver metastases, and uninvolved non-malignant pancreas. Robust nuclear localization of FRA-1 was observed in primary and metastatic tumor cells whereas uninvolved pancreas showed lower levels of diffuse cytoplasmic staining.

Based on these results, we hypothesize that FRA-1 plays an important role in a subset of pancreatic cancers by altering the binding profile of AP-1. Due to a dependence on ERK activity for FRA-1 function, we propose that cancers with activating mutations in the RAS-RAF-MEK-ERK cascade are the most likely candidates for utilization of FRA-1.

Citation Format: Ryan L. Hanson, Michael A. Hollingsworth. Identification of FRA-1 as a potential driver of pro-invasive properties in pancreatic cancer in conjunction with MUC1. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 508. doi:10.1158/1538-7445.AM2015-508