Identification of cellular proteases involved in influenza A virus replication

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Hagan, Mable
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Nature Publishing Group
Influenza viruses circulate worldwide and are a serious public health concern, causing annual epidemics of human respiratory tract infections. Reassortment of gene segments between different strains of influenza can generate new pandemic strains, like the 2009 H1N1 pandemic and the current H7N9 avian influenza virus. Vaccines are the most effective option to limit the impact of a pandemic, however preparation of a new vaccine takes months. Antiviral treatment is recommended until a vaccine is available, however the efficacy of current antivirals is highly susceptible to the development of resistance. These pitfalls prioritize the need to discover new compounds targeting essential functions of the virus. My thesis focuses on the identification of cellular proteases that are required for influenza virus replication to develop as potential antiviral targets. Proteolytic cleavage of influenza virus hemagglutinin (HA) is essential for infectivity. Although several cellular proteases have shown HA cleaving activity, these proteases demonstrate significant variation in the cleavage efficiency across the HA subtypes found in human and avian viruses, including some subtypes that are not cleaved by any of these proteases. This work aimed to identify novel cellular proteases that are involved in HA activation by using a human protease siRNA library to screen Caco2 cells infected with a seasonal GFP-expressing influenza virus. Potential proteases identified were validated using wild-type influenza viruses of different subtypes. The most promising protease candidate identified was MASP1, and a MASP1 stably-knocked down Caco2 (MASP1-KD) cell line was generated. MASP1 was shown to be essential for efficient replication of a broad range of influenza virus subtypes. Assessment of where MASP1 fits into the influenza virus life cycle revealed that MASP1 most likely is involved in later stages of viral replication. Comparison of the proteomic profiles between Caco2 and MASP1-KD cells further revealed possible cellular pathway interactions that MASP1 may be involved in. The discovery of a new role for MASP1 in the replication of influenza viruses, and possibly other viral families, provides a strong foundation for future studies to evaluate the effectiveness of MASP1 therapeutics and expands our knowledge of virus and host biology.
Influenza virus, cellular proteases
Hagan M, Ranadheera C, Audet J, Morin J, Leung A and Kobasa D. (2016) Post-exposure treatment with whole inactivated H5N1 avian influenza virus protects against lethal homologous virus infection in mice. Scientific Reports. Jul 12;6:29433.