Human bocavirus (HBoV) is associated with acute expiratory wheezing and pneumonia. The HBoV genome has been frequently detected worldwide, ranging from 2%-19%, in respiratory specimens from young children with acute respiratory illnesses. Differentiated human airway epithelial cells have been recently shown to support HBoV replication;however, a high virus load is required. An infectious DNA clone of HBoV has not been constructed, which impairs study of the pathogenesis of this virus. Minute virus of canines (MVC), a canine bocavirus, causes respiratory diseases with breathing difficulty and enteritis with severe diarrhea in pups. MVC infection of permissive WRD cells perturbs cell progression at the S-phase in favor of viral replication in early infection and at the G2/M-phase in later infection, and ultimately leads to an apoptotic cell death. In addition, a DNA damage response is detected during MVC infection. Therefore, cell death induced by MVC infection, which is independent of both nonstructural and structural viral proteins, must be a host defense mechanism, presumably the DNA damage response, designed to arrest viral replication by eliminating infected cells, and must be regulated. In addition, bocaviruses are unique among parvoviruses in that a third ORF, the mid-ORF, encodes a novel non-structural protein, NP1. Because of the similarities between HBoV and MVC, both in the organization and sequence of the genomes and in the symptoms of caused diseases, study of the canine Bocavirus MVC will eventually answer questions about the functions of NP1 in Bocavirus DNA replication and the molecular basis of Bocavirus-induced cell cycle arrest and cell death. Ultimately, knowledge obtained from study of MVC will help us to understand the molecular pathogenesis of HBoV. In this application, we propose to discover the function of the NP1 protein in Bocavirus DNA replication, especially, to identify cellular factors that interact with the NP1;and how Bocavirus infection arrests the cell cycle and causes an apoptotic cell death;and attempt to construct an infectious clone of HBoV from clinical specimens. In addition, the strategy that Bocavirus infection uses to induce a DNA damage response, leading to cell cycle arrest and cell death, is unusual in that viral proteins are not involved. Examining this strategy within the tractable biological system of Bocavirus provides us an attractive opportunity to gain insight into the basic cellular mechanism involved in defending against viral infection.
Human bocavirus is pathogenic to humans, causes lower respiratory tract infections in children. Study of the animal bocavirus will help us to understand the replication and pathogenesis of the bocaviruses in general. Our experiments will thus answer critical questions in the pathogenesis of human bocavirus infection, and have the potential to provide prophylactic and therapeutic interventions to diseases caused by human bocavirus.
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