Proteomic Profiling of Protease-Primed Virus-Permissive Caco-2 Cells Display Abortive-Interferon Pathway and Deregulated Thromboinflammatory SERPINS
Authors: Sharma Maryada , Panda Naresh K. 
Published: June 2020

Emerging paradigms in interferon (IFN) biology suggest a dynamic INF induced interactome that extends through broader Interferon Stimulated Gene (ISG)- induction, which implicates interferon- ISG coordinated cross-talk with mRNA processing, post-translational modification and metabolic processes that underlie pathological (viral, autoimmune and tumor biology) and physiological (stem cell regenerative pathways) processes. INF immune responses can also be triggered by endogenous host-derived molecules that are generated in response to cellular stress or hemostasis imbalance to establish tissue repair and regeneration in first place, however, overactivation or lack of countermeasures can result in host tissue damage. The proteases are integral to viral and tumor pathology, and importantly serine proteases TMPRSS2 and trypsin have been identified as important molecular determinants underlying COVID-19 pathology, and emergence of coronaviruses cultured in vitro, respectively. We propose that pathogen associated proteases can act as novel stress-inducers to facilitate viral- competent immunomodulation. We term it as Protease Induced Transcriptomic/ epi-Transcriptomic Reshaping (PITTR) of host cells to counter cellular stress. We present a novel experimental model and our preliminary findings of trypsin- primed Caco-2 cells (CPT) that result in translational halt comparable to cells grown under serum-starvation conditions (CSS). CPT at escalating trypsin concentration (CPT- EC) induce upregulation of selective proteins that majorly map to ribosomal, RNA transport, and spliceosome ribonucleoproteins (RNPs). The inclusion of proinflammatory IL1-b to CPT (CPT- IL) resulted in global overexpression of proteins comparable to Caco-2 cells cultured in growth-factor rich serum conditions (CFBS), indicating a likely de-repression of trypsin- induced translational halt. Caco-2 cells display abortive interferon proteome under differential trypsin conditions (CPT, CPT-EC and CPT-IL), which is marked by complete lack of INF generation despite induction of intermediate ISGs, suggestive of protease (trypsin)- dependent regulation of INF response. Viruses regulate the proteome of stress granules (SGs) that are induced to cope transient translational halt as a central adaptive response to pathogen induced cellular stress. The integral components of SGs include non-translating mRNA, ribonucleoproteins (RNPs) and RNA binding proteins (RBPs), which together form biological condensates through a biophysical process involving weak electrostatic interactions through intrinsically disordered regions in RBPs resulting in liquid- liquid phase separation. We compared the CPT- EC proteome to the Mammalian Stress Granules Proteome (MSGP) database to explore potential RBPs that could possibly regulate INF response (and could act as potential anti-viral targets). Notably, differentially upregulated RNPs and potential RBPs from ISG family including ADAR and PRKRA, and RNA helicases implicated in viral pathogenesis were found to be upregulated in the CPT- EC proteome further strengthening the role of proteases (trypsin) in regulating INF pathways independent of the pathogen. We propose that the supplementation of viable SARS-CoV-2 viral loads to trypsin- primed host cells could recapitulate an infectious disease model, which may closely phenocopy pathogen- driven inflammation and signaling events. Based on the global downregulation of seven SERPINS (serine protease inhibitors) linked to thromboinflammation in our LCMS profiling data, we support the candidature of serine protease inhibitors for protease mediated viral pathologies. COVID-19 is increasingly linked to coagulopathy and resemblance to Neutrophil Extracellular Trap (NET) related thromboinflammatory features; SERPIN A1AT (alpha 1 antitrypsin) being a potent neutrophil- elastase inhibitor and a negative regulator of coagulation complement pathway may be a promising candidate for establishing hemostasis rebalancing in COVID-19 pathology.