Abstract 1728 Alternative Splicing of the Innate Immune Regulator IRF7 Across Cell Types and in Response to Immune stimuli

Alternative Splicing (AS) is a ubiquitous process in which a primary RNA transcript is processed by variable inclusion of exon and intron elements. This process is primarily regulated by functional cis-regulatory elements in the pre-mRNA and the trans-acting factors (RNA-binding proteins) that recognize and bind to these cis-elements to either promote or suppress the assembly of spliceosome at adjacent splice sites. Studies have shown that, upon T-cell Receptor (TCR) activation, a significant number of genes associated with various signaling pathways, including the type-1 interferon (IFN) signaling pathway, are alternatively spliced. The underlying regulatory mechanisms of AS events of the IFN-signaling molecules and their impact on overall innate immune signaling network are yet to be fully understood. Our study focuses on a specific AS event of the Interferon Regulatory Factor-7(IRF7), a master transcription factor in type-1 IFN signaling involving the retention of intron 1. Splicing of intron 1 results in the canonical form of IRF7 (cIRF7) while retention of intron 1 results in an alternate translation start site leading to an N-terminally extended form of IRF7 (exIRF7). We have found that stimulation of both Jurkat T cells and A549 lung epithelial cells by viral infection or drugs that target known immune signaling receptors –PMA, Poly I:C, and LPS- cause changes in expression of two isoforms of IRF7 in a signal and time specific manner. We also find differences in IRF7 expression across distinct primary hematopoietic cell types. Using CRISPR gene editing to force sole expression of one isoform, studies are in progress to determine the functional differences of these isoforms in cellular gene expression and viral infectability. Determining the functional differences of the splice variants will enhance our understanding on regulation of signal-induced splicing events, particularly intron-retention, and role of such events in modulating cellular type-1 IFN response.