Poxvirus host range genes.

As a family of viruses, poxviruses collectively exhibit a broad host range and most of the individual members are capable of replicating in a wide array of cell types from various host species, at least in vitro. At the cellular level, poxvirus tropism is dependent not upon specific cell surface receptors, but rather upon: (1) the ability of the cell to provide intracellular complementing factors needed for productive virus replication, and (2) the ability of the specific virus to successfully manipulate intracellular signaling networks that regulate cellular antiviral processes downstream of virus entry. The large genomic coding capacity of poxviruses enables the virus to express a unique collection of viral proteins that function as host range factors, which specifically target and manipulate host signaling pathways to establish optimal cellular conditions for viral replication. Functionally, the known host range factors from poxviruses have been associated with manipulation of a diverse array of cellular targets, which includes cellular kinases and phosphatases, apoptosis, and various antiviral pathways. To date, only a small number of poxvirus host range genes have been identified and studied, and only a handful of these have been functionally characterized. For this reason, poxvirus host range factors represent a potential gold mine for the discovery of novel pathogen-host protein interactions. This review summarizes our current understanding of the mechanisms by which the known poxvirus host range genes, and their encoded factors, expand tropism through the manipulation of host cell intracellular signaling pathways.