Research Interest:
PIV5 & Host Interactions

PIV5 is a member of the Rubulavirus genus of the family Paramyxoviridae which includes many important human and animal pathogens such as mumps virus, human parainfluenza virus type 2 and type 4, Newcastle disease virus, Sendai virus, HPIV3, measles virus, canine distemper virus, rinderpest virus and respiratory syncytial virus. Although PIV5 was originally isolated from cultured primary monkey cells its natural host is the dog in which it causes kennel cough. PIV5 can infect humans and isolates have been obtained from human sources, but no known symptoms or diseases in humans have been associated with PIV5.

Unlike most paramyxoviruses, PIV5 can infect many cells with little cytopathic effect (CPE) and PIV5 infection does not induce apoptosis. For example, PIV5 can grow in MDBK cells productively up to 40 days without severe CPE. The ability of PIV5 to grow productively without inducing CPE suggests that PIV5 may have mechanisms to evade host defense responses such as apoptosis.

PIV5 encodes eight known viral proteins. Nucleocapsid protein (NP), phosphoprotein (P), V protein and large RNA polymerase (L) protein are important for transcription and replication of the viral RNA genome. The V protein causes degradation of signal transducer and activator of transcription (STAT) 1 protein, a key protein for interferon responses, in human cells and slows down cell cycle. The fusion (F) protein, a glycoprotein, mediates both cell-to-cell and virus-to-cell fusion in a pH-independent manner that is essential for virus entry into cells. The hemagglutinin-neuraminidase (HN), another viral glycoprotein, is also involved in virus entry and release from the host cells. The matrix (M) protein is thought to play an important role in virus assembly. Unlike most paramyxoviruses, PIV5 encodes a small hydrophobic (SH) integral membrane protein located between the genes for the glycoproteins F and HN. The SH protein is a 44-residue hydrophobic integral membrane protein and is oriented in membranes with its N terminus in the cytoplasm.

The SH gene was deleted from cDNA of the PIV5 genome and a viable virus was recovered using a reverse genetics system. The virus (rPIV5ΔSH) caused increased CPE and apoptosis in MDBK cells (bovine cell line), L929 cells (mouse cell line) and MDCK cells (canine cell line), but not in HeLa T4 and A549 cells (human cell lines).rPIV5ΔSH was indistinguishable from the wild type SV5 virus in single-step growth curve, plaque size, viral protein and viral mRNA synthesis. Co-infection of rPIV5ΔSH with PIV5 did not result in CPE, which lends support to the notion that expression of the SH protein is the key factor in preventing apoptosis.

Examination of rPIV5ΔSH in a small animal model system showed that it was attenuated in vivo as compared to wild-type rPIV5, even though it caused vastly greater CPE in mouse, bovine and canine cell types, a finding consistent with the notion of clearance of apoptotic cells in a host species.

PIV5 provides a good model system to understand how paramyxoviruses induce and inhibit apoptosis. Activation of apoptotic cascades can be studied using rPIV5ΔSH and inhibition of apoptosis can be studied using wild type PIV5 virus. Additional mutant PIV5 viruses that induce apoptosis in infected cells can be obtained by manipulating PIV5's RNA genome using a reverse genetics system and studied. Pathogenicity of mutant PIV5 viruses can be examined in vivo using a small animal model system.