Abstract

Bovine Parvovirus (BPV) belongs to the genus Bocavirus, family Parvoviridae. BPV is the leading etiologic agent among the pathogens that cause primary gastroenteritis of cattle. Many of the intracellular events associated with virus replication are unknown. In this research project, we investigated BPV internalization into the host cell and trafficking in the cytosol. Preliminarily, EBTr cells had abundant clathrin, virus attached to purified clathrin, and EM micrographs revealed virus in endocytic vacuoles. Assays detecting virus infectivity (i.e. viral protein synthesis), virus production (completion of the replication cycle), and quantitative PCR (qPCR) to detect viral transcripts were used to evaluate virus uptake and subsequent trafficking events in the presence of selective inhibitors. Cell toxicity mediated by the drugs was evaluated by the MTT test. Virucidal effects of the drugs were assessed. A control virus was used to verify the inhibitor technology. Immunofluoresceinated virus particles were found in clathrin-rich early endosomes. Clathrin-mediated endocytosis (CME) was examined by clathrin polymerization inhibiting agent (chloropromazine), lysosomotropic agents (ammonium chloride and chloroquine), a vacuolar ATPase inhibitor (bafilomycin A1), and a blocker of transition between endosomes (brefeldin A). Caveosome pathway inhibitors included phorbol 12-myristate 13-acetate (a suppressor of caveolae formation), nystatin and methyl-beta-cyclodextrin (lipid raft blockers), and genistein (a tyrosine kinase phosphorylation inhibitor). Trafficking of BPV was investigated using specific inhibitors of proteasomal activity, actin-myosin function, and microtubule-dynein function. The proteasomal protease suppressor (lactacystin), and a proteasomal chymotrypsin inhibitor (epoxomicin) were used. The role of actin was probed by cytochlasin D, latrunculin A, and ML-7. The microtubule inhibitors nocodazole, vanadate, and EHNA were used to probe microtubule function. The inhibitors of CME reduced virus production and reduced infectivity, a result confirmed by qPCR. The blockers of caveolin-mediated entry did not interfere with virus production nor virus infectivity. Proteasome activity blockage did not affect the virus replication. But the virus cycle was affected by actin blockage and by microtubule blockage detected by qPCR. Taken together these data indicate that BPV uptake is mediated by clathrin coated pits and is acid-dependent. Further processing of BPV in the cytosol does not require proteasomal enzymes. Actin-associated vesicular transport appears to be essential to virus replication and trafficking to the nucleus appears to be mediated by microtubules.

Degree

PhD

College and Department

Life Sciences; Microbiology and Molecular Biology

Rights

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