Molecular and functional characterization of peroxisomal MAVS in innate immunity

Abstract

MAVS is a critical adaptor in the signalling pathway of type I interferon (IFN) production. The importance of peroxisomes in antiviral response arose from the findings that MAVS resides on peroxisomes. MAVS forms functional aggregates on the mitochondria surface for signal propagation, whether MAVS also forms aggregates at peroxisomes remains uncharacterized. Previous work has showed that peroxisomal MAVS induces type I IFN-independent induction of certain ISGs in a rapid but transient manner, distinguishing itself from mitochondrial MAVS. This project aims to explore the key differences, concerning the aggregates formation and signalling kinetics, between peroxisomal and mitochondrial MAVS. We hypothesized that MAVS aggregation is dispensable for peroxisomal MAVS-mediated signalling as peroxisome surface is unlikely to support MAVS signalosome formation. To characterize the MAVS-mediated signalling from peroxisomes, the strategy to separate the putative mitochondrial and peroxisomal functions is of great importance. In view of the finding that tail-anchored proteins with high positive charges at tail sequence tend to be targeted to peroxisomes, we generated U2OS MAVS KO cells stably expressing wild type MAVS and mutants with higher or lower positive charged tails. Confocal microscopy has revealed that MAVS localization is highly dependent on the tail charge, suggesting MAVS utilizes its tail sequence to localize to both mitochondria and peroxisomes. Upon SeV infection, significant IFN-β mRNA level and secretion were detected in MAVS KO cells reconstituted with peroxisome-targeted MAVS. Functionally, our work has demonstrated that overexpression of aggregation-defective mutants induces robust expression of type I IFN and ISGs in peroxisomal MAVS but not in wild type and mitochondrial MAVS, suggesting that peroxisomal MAVS mediates type I IFN response in an aggregation-independent manner. Collectively, our evidence suggests that peroxisomal MAVS exhibits the ability to induce type I IFN in both overexpression and stable gene expression model. Our work showcases that aggregation is dispensable for peroxisomal MAVS mediated signalling, providing insights into the multifaceted MAVS in innate immune signalling.

Targeting MAVS to peroxisomes is achieved by subtly increasing the positively charged residues at the tail region of MAVS, highlighting the functional role of tail charge in subcellular targeting of MAVS.