Influenza virus pathogenicity is determined by caspase cleavage motifs located in the viral proteins

Abstract

Almost all influenza virus proteins are found to contain caspase cleavage motifs. Two caspase cleavage consensus sequences, EXD↓Y and D/EXXD↓Y (caspase motifs) were identified in N- and C-terminal regions of influenza virus proteins nucleocapsid NP (positions D16 and D497) and ionic channel M2 (positions D23 and D87). Using reverse genetics with the highly-virulent avian influenza virus A/FPV/Rostock (H7N1), as a vector precursor, these NP and M2 caspase motifs were artificially altered by site-directed mutagenesis and pathogenicity of the generated caspase mutant viruses was tested in chickens. Three main groups of virus mutants were identified. The first group of mutants was characterized by high replication in cells and low virulence in chickens. These virus mutants possessed the altered N-terminal NP and C-terminal M2 caspase motifs. The second group of virus mutants, possessing the altered N-terminal caspase motif of M2, was characterized by attenuated replication in cultured cells and reduced pathogenic properties in chickens. Third, mutations generated in the C-terminus of NP were lethal and restricted virus rescue by reverse genetics, implying a critical role of this caspase site in virus replication. Thus, these data suggested that, (i) caspase motifs in virus proteins play a significant role in virus pathogenicity; (ii) the lack of direct correlation between replication potential and pathogenicity, observed in caspase mutants of the first virus group, implied that virus caspase motifs could affect immunopathogenesis during the infection process, rather than simply controlling virus production in target cells in the chicken host.

Caspase Cleavage Motifs of Influenza Subtypes Proteins: Alternations May Switch Viral Pathogenicity

“…As shown in table 1, the caspase recognition motifs VDVD in M2, DDVD in PB2, and EEYD in NP proteins are conserved amongst H9N2, H5N1 viruses. These motifs were also reported for H7N1 subtype (13). The lack of caspase cleavage motif for M1 and NS2 proteins of these viruses is in agreement with that reported for avian H7N1 subtype.…”

“…A variety of host and viral factors are involved in induction of apoptosis that may depend on the cell type (8)(9)(10)(11)(12). The regulation of some host apoptotic factors like cysteinyl-aspartatekinases (caspases) activation interacts with influenza virus replication and pathogenicity (13,14). Generally, during the highly regulated form of cell death, a cascade of caspases is activated and lead to cleavage of many structural and regulatory proteins and involve many physiological and pathological processes (15,16).…”

Structure, Function, and Evolution of the Crimean-Congo Hemorrhagic Fever Virus Nucleocapsid Protein

“…Intriguingly, the nucleocapsid protein (NP) of human-infecting strains of influenza A virus also possesses caspase cleavage sites which have been shown to possess important roles in the virus life cycle (51,52). Infectious influenza viruses bearing mutations that abrogate caspase cleavage at an N-terminal recognition site could not be rescued, indicating that such alterations are lethal to virus viability, whereas mutations within a C-terminal caspase cleavage site rapidly reverted to the wild type to restore cleavability.…”

Bik Mediates Caspase-Dependent Cleavage of Viral Proteins to Promote Influenza A Virus Infection

“…Furthermore, cleavage of viral proteins by host cell proteases and protease cleavage motifs have been identified in proteins encoded by IAVs (18,37,38). Because IAVinduced activation of caspase 3 was inhibited in bik 2/2 MACEs and shBik HAECs, we tested whether viral proteins are cleaved in a Bik-dependent manner.…”