Host- and Strain-Specific Regulation of Influenza Virus Polymerase Activity by Interacting Cellular Proteins

ABSTRACT Highly pathogenic avian influenza A (HPAI) viruses of the H5N1 subtype have recently emerged from avian zoonotic reservoirs to cause fatal human disease. Adaptation of HPAI virus RNA-dependent RNA polymerase (PB1, PB2, and PA pro-teins) and nucleoprotein (NP) to interactions with mammalian host proteins is thought to contribute to the efficiency of viral RNA synthesis and to disease severity. While proteomics experiments have identified a number of human proteins that associate with H1N1 polymerases and/or viral ribonucleoprotein (vRNP), how these host interactions might regulate influenza virus poly-merase functions and host adaptation has been largely unexplored. We took a functional genomics (RNA interference [RNAi]) approach to assess the roles of a network of human proteins interacting with influenza virus polymerase proteins in viral poly-merase activity from prototype H1N1 and H5N1 viruses. A majority (18 of 31) of the cellular proteins tested, including RNA-binding (DDX17, DDX5, NPM1, and hnRNPM), stress (PARP1, DDB1, and Ku70/86), and intracellular transport proteins, were required for efficient activity of both H1N1 and H5N1 polymerases. NXP2 and NF90 antagonized both polymerases, and six more RNA-associated proteins exhibited strain-specific phenotypes. Remarkably, 12 proteins differentially regulated H5N1 polymerase according to PB2 genotype at mammalian-adaptive residue 627. Among these, DEAD box RNA helicase DDX17/p7