Abstract 6326: Global changes in alternative mRNA polyadenylation profile promote the development of multidrug resistance (MDR) to chemotherapy in colon cancer
Authors: To Kenneth KW 
Published: September 2020

Abstract
Aim: The study investigated the global changes in mRNA alternative polyadenylation (APA) profile associated with MDR development in colon cancer cells.
Background: Polyadenylation is a crucial step needed for the maturation of eukaryotic mRNAs. APA refers to the production of different mRNA isoforms bearing varying length of 3'-untranslated region (3'UTR), where key RNA regulatory elements are found. APA usually eliminates the distal end of the 3'UTR, thus allowing the escape from the predominantly repressive effect from longer 3'UTR. Colon cancer is a leading cause of cancer-related death worldwide. MDR, which is usually associated with overexpression of ATP-binding cassette efflux transporters including ABCG2, is a major unresolved obstacle to successful cancer chemotherapy. We have previously reported that ABCG2 mRNA is more stable in MDR colon cancer cells. Interestingly, the increase in mRNA stability is tied to a missing microRNA binding site (miR-519c) due to the shortening of ABCG2 mRNA 3'UTR in drug resistant cells. Thus microRNA-mediated mRNA degradation and/or protein translation block are relieved, thereby leading to ABCG2 overexpression. A remarkable feature of 3'UTR APA is that it can be regulated globally, thus simultaneously affecting numerous mRNA transcripts. While ABCG2 mRNA 3'UTR is shortened in MDR colon cancer cells, the global changes in APA profile of other transcripts during the course of MDR development have not been reported.
Method: Differential APA signature and specific APA-regulated mRNAs were evaluated in two pairs of sensitive and MDR colon cancer cell lines by RNA sequencing. APA profiles were assessed from the RNA-Seq datasets by using the bioinformatics tool “DaPars”. Altered 3'UTR isoforms of a few differentially expressed mRNAs were validated by 3'RACE assay and 3'UTR isoform specific PCR analysis. The genes were subjected to Gene Ontology (GO) analysis to identify relevant molecular pathways and biological processes.
Result: APA profiles of two pairs of drug resistant ABCG2-overexpressing colon cancer cell line (S1-M1-80 & SW620 Flv100) versus their parental cells (S1 & SW620) were compared at the global scale from their sequenced RNA samples. By GO analysis using the PANTHER Platform, mRNA transcripts exhibiting 3'UTR shortening in S1-M1-80 and SW620 Flv100 versus their respective parental cells were enriched in biological processes including “transport and catabolism”, “cell growth and death”, and “cell motility” by GO terms. Genes ranked at the top of the list are mostly direct or indirect targets of the Wnt-β-catenin signaling pathway. Wnt signaling is a crucial pathway for mediating metastasis and therapeutic resistance.
Conclusion: Global changes of APA in gene regulation may contribute to the development of MDR in colon cancer. Further investigation is warranted to elucidate the mechanisms leading to APA. Modulation of the APA machinery may help eradicate MDR cancer cells.
Citation Format: Kenneth KW To. Global changes in alternative mRNA polyadenylation profile promote the development of multidrug resistance (MDR) to chemotherapy in colon cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6326.