Influenza virus expresses transcripts early in infection and transitions towards genome replication at later time points. This process requires de novo assembly of the viral replication machinery, large ribonucleoprotein complexes (RNPs) composed of the viral polymerase, genomic RNA and oligomeric nucleoprotein (NP). Despite the central role of RNPs during infection, the factors dictating where and when they assemble are poorly understood. Here we demonstrate that human protein kinase C (PKC) family members regulate RNP assembly. Activated PKCδ interacts with the polymerase subunit PB2 and phospho-regulates NP oligomerization and RNP assembly during infection. Consistent with its role in regulating RNP assembly, knockout of PKCδ impairs virus infection by selectively disrupting genome replication. However, primary transcription from pre-formed RNPs deposited by infecting particles is unaffected. Thus, influenza virus exploits host PKCs to regulate RNP assembly, a step required for the transition from primary transcription to genome replication during the infectious cycle. eLife digest To be able to multiply, the influenza virus needs to enter the cells of its host and trick them into copying the virus’ genetic information and assembling new virus particles. The genetic information of the virus is stored in molecules of ribonucleic acid (RNA) and encodes several viral proteins that are involved in making the new virus particles. These proteins include an enzyme known as the viral polymerase and a “nucleoprotein”. The viral polymerase copies the RNA and then the nucleoprotein binds to the new RNA to protect it until it is packaged into new virus particles. Many nucleoprotein units assemble into long chains that coat the whole length of the RNA, but it is not yet known exactly how this process is controlled. In cells, other enzymes known as kinases are able to alter the activities of many proteins by modifying the structures of proteins by a process called phosphorylation. Influenza nucleoprotein was previously shown to be phosphorylated. It is therefore possible that the influenza virus may use phosphorylation to control the assembly of nucleoproteins into chains along the RNA. However, the virus’ RNA does not encode any kinase enzymes of its own, so it must rely on kinases from its host cell. Human cells produce many kinase enzymes that can be grouped into several different protein families. Mondal et al. studied the role of the protein kinase C family in making new virus particles. The experiments show that modifying the members of this protein family to be permanently active causes the viral nucleoprotein to be phosphorylated at two specific sites on the protein. This regulates the assembly of the nucleoproteins into long chains on the RNA, and ultimately promotes the production of new virus particles. Closer examination revealed that this effect was primarily down to one specific kinase known as PKCδ. The virus was less able to multiply in human lung cells that were missing PKCδ – specifcially because the formation of nucleoprotein chains was no longer regulated – and these cells produced lower quantities of virus proteins. Taken together, these findings show that kinases produced by host cells can control the ability of viruses to replicate by modifying the viral nucleoproteins. In the future, it may be possible to develop new drugs that target PKCδ and other cellular factors the virus needs to help treat influenza infections.
【저자키워드】 Human, Influenza virus, nucleoprotein, Other, protein kinase C, kinase, polymerase,