Role of 2',5'-Oligoadenylate (2-5A) and RNA Cleavage in Anti- Inflammatory Response by Novel Nuclear Factor Kappa B (NF-kB) Inhibitor ASCC1

Abstract

The OAS/RNase L pathway is a principal mediator of the IFN-I induced anti-viral response. Second messenger 2’-5’ linked oligoadenylates (2-5A) generated by OAS are required to bind and activate latent endoribonuclease RNase L for cleavage of single-stranded RNA (ssRNA) from both viral and cellular sources. AKAP7 has been identified as the only known mammalian 2’5’-phosphodiesterase (2’5’-PDE), involved in limiting RNase L activity by regulating 2-5A turnover. Performing a bioinformatics screen, we identified scarcely known gene ASCC1 as possessing a C-terminal catalytic active site sequence homologous to AKAP7, and a KH RNA binding domain. We hypothesized ASCC1 is involved in innate immune system regulation and could possess similar 2’,5’- PDE and/or RNase activity. After generating full-length and delΔ1-79 (conserved catalytic site only) ASCC1 constructs, phosphodiesterase and RNase cleavage assays demonstrated ASCC1 does not degrade 2-5A or cleave ssRNA through individual nucleotide specificity respectively. Quantitative RT-PCR confirmed roughly 2-fold downregulation of pro-inflammatory NF-κB genes IL-6, IL-8, and TNF in HeLa cells overexpressing full-length ASCC1, corroborating previous evidence ASCC1 functions as a NF-κB inhibitor. Future directions should be aimed at determining ASCC1’s RNA binding mechanism and further characterizing its role as a NF-κB regulator in the anti-inflammatory response. Doing so would allow us to better understand the underlying basis for the association between germline ASCC1 mutations with genetic predisposition to chronic inflammatory disorders like rheumatoid arthritis, and further knowledge about mechanisms/pathways involved in regulating innate immune response.