The effect of cellular context on miR-155 mediated gene regulation in four major immune cell types (PolyA-Seq)

Numerous microRNAs and their target mRNAs are co-expressed across diverse cell types. However, it is unknown whether they are regulated in a cellular context-independent or -dependent manner. Here, we explored transcriptome-wide targeting and gene regulation by miR-155, whose activation-induced expression plays important roles in innate and adaptive immunity. Through mapping of miR-155 targets using differential Argonaute iCLIP, mRNA quantification with RNA-Seq, and 3'UTR usage analysis using polyadenylation (polyA)-Seq in activated miR-155-sufficient and deficient macrophages, dendritic cells, T and B lymphocytes, we identified numerous targets differentially bound by miR-155. While alternative cleavage and polyadenylation (ApA) contributed to differential miR-155 binding to some transcripts, in a majority of cases identical 3'UTR isoforms were differentially regulated across cell types, suggesting ApA-independent and cellular context-dependent miR-155-mediated gene regulation reminiscent of sequence-specific transcription factors. Our study provides comprehensive maps of miR-155 regulatory RNA networks and offers a valuable resource for dissecting context-dependent and -independent miRNA-mediated gene regulation in key cell types of the adaptive and innate immune systems. Overall design: Primary dendritic cells, B cells, CD4 T cells, and macrophages from C57BL/6J wild type and miR-155 KO mice were cultured in RPMI medium with 10% FBS. Prior to harvesting primary dendritic cells, mice were subcutaneously injected with one million B16 melanoma cells expressing Flt3 ligand for about two weeks. After purification of splenic CD11c+ dendritic cells by CD11c microbeads (Miltenyi Biotec), dendritic cells were activated in a medium containing 100 ng/ml LPS (SIGMA) and 20 ng/ml GMSCF (Tonbo). Splenic primary B cells were purified by negative selection using Dynabeads Mouse CD43 (Invitrogen), and activated in a medium containing 25 ug/ml LPS and 6.5 ng/ml mIL4 (PeproTech). CD4 T cells from lymph node and spleen were purified with Dynabeads FlowComp Kit (Invitrogen). CD4+CD25-CD44- T cells were then activated with Dynabeads Mouse T-Activator CD3/CD28 (Invitrogen). Intraperitoneal macrophages, induced by thioglycollate injection, were harvested and activated with 100 ng/ml LPS.

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Hsin JP, Lu Y, Loeb GB, Leslie CS, Rudensky AY