Systematic Evaluation of Role of Cathepsins in the late Stage of Influenza A Virus Infection

Abstract

Influenza A virus (IAV) causes acute respiratory viral infection which affects millions of people globally every year. As IAV evolves at an extremely fast rate due to its mutation-prone RNA genome, vaccines need to be annually re-calibrated to provide protection against the viral infection. Supplementing vaccine protection, the available anti-influenza drug portfolio constitutes an important arsenal to fight against the virus. However, there is growing evidence on the emergence of drug-resistant viral mutants, which threatens the current treatment regime and warrants the identification of new anti-influenza agents with high barrier to resistance. Since all the approved anti-influenza drugs target the virus-encoded proteins and since the viral proteins rapidly acquire mutations, the possibility remains on the emergence of viral variants, capable of subverting drug inhibition. An attractive approach in the therapeutic management of influenza is to identify and target the host factors, which are manipulated by IAV to complete its life cycle. Therefore, a comprehensive understanding of the host’s contribution to viral infection is of paramount importance to illuminate potential host targets and evaluate their suitability in therapeutic interventions. Among several host factors that have recently been implicated in viral infections, the endo/lysosomal cathepsins have emerged as critical players. In this study, we aimed to systematically evaluate the role of cathepsins in the late phase of IAV infection. Cathepsins are lysosomal protease majorly involved in protein degradation and cellular homeostasis. They are synthesized in precursor form in the ER and are trafficked via Golgi to the endo-lysosomal compartments. This study reveals that in the late stage of IAV infection, cathepsins showed cytoplasmic translocation and co-localized with viral hemagglutinin (HA). It was observed that upon lysosomal membrane permeabilization cathepsins are released from the lysosomal compartment into the cytosol. LAMP1 appeared to be degraded during the late stage of infection. Also, we observed localization change for cathepsin H (CTSH) depletion of mannose-6-phosphate receptor (M6PR). Together, this work suggests that cathepsins may play a critical role in the IAV assembly or egress processes. XV