Abstract A062: The effects of cellular context on miR-155 mediated regulation of gene expression

Abstract

Abstract MicroRNA-155 (miR-155) is involved in differentiation and regulation of responses of multiple haematopoietic cell types. Its dysregulation is implicated in many human malignancies, e.g. Hodgkin, diffuse large B lymphomas, and breast cancer. Many microRNAs and their target mRNAs are co-expressed in diverse types of cells and tissues. To what extent the interaction between a specific microRNA and its target mRNAs is preserved in different cellular context is largely unknown. We employed genome-wide approaches to investigate whether regulation of commonly expressed mRNA by miR-155 operates in a cell type-specific manner in analogy to cell-context dependent regulation by transcription factors. We first performed RNA-Seq to quantitatively measure mRNA expression levels in primary B cells, dendritic cells, macrophages, and CD4+ T cells from wild type and miR-155 knockout mice. We found many miR-155 target mRNAs that contain seed matches in 3' untranslated regions (3'UTRs) were differentially repressed between four types of primary immune cells. Next, we performed iCLIP (individual-nucleotide resolution UV crosslinking and immunoprecipitation) to precisely map Argonaute 2 binding. Quantitative analysis of iCLIP in both wild type and miR-155 KO primary cells uncovered hundreds of miR-155 bound genes, a large number of which overlapped the cohorts of genes that were identified by RNA-Seq as differentially regulated by miR-155. Most mRNAs are alternatively polyadenylated, and through alternative polyadenylation (ApA) mRNAs can acquire or lose microRNA sites. To account for ApA, we carried out PolyA-Seq to measure polyadenylation site usage, and found that ApA contributed to differential miR-155 regulation of a number of genes. However, in many cases the same target 3'UTR isoforms were differentially regulated between cell types, suggesting ApA-independent mechanisms of miR-155 specificity, and cellular context dependent miR-155-mediated regulation of gene expression. This research will elucidate mechanistic underpinning of cell-context dependent microRNA function, and help understand miR-155 functions in disease, specifically in lymphomas and other cancers. Citation Format: Jing-Ping Hsin, Yuheng Lu, Christina S. Leslie, Alexander Y. Rudensky. The effects of cellular context on miR-155 mediated regulation of gene expression [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A062.