Secretion of PRRS virrus GP3 glycoprotein controversy: GP3 characterization and role identification in vitro and in vivo

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The most important viral disease in term of economical lost in swine industry worldwide is the Porcine Reproductive and Respiratory Syndrome (PRRS). The etiological agent of PRRS, PRRS virus (PRRSV) is classified in two distinct genotypes, the North American (NA) and the European (EU), which possess a nucleotide sequence identity of 63% when compared one to another. Presently, the efficacy of commercial vaccines is quite mitigated. Consequently, to improve prophylactic methods, it is important to characterize and establish the roles and functions of the viral proteins of PRRSV. Those improvement could be beneficial for both veterinary pharmaceuticals and porcine industries. Until now, the function of the GP3 glycoprotein, encoded by the ORF3 gene of PRRSV is unknown, based on conflicting data existing between the GP3 of both genotypes. At first in 1996, the GP3 of the EU reference strain Lelystad (LV) was reported to be a structural protein of the virion, but in 1998, following the modification and improvement that was made by our team in the virus purification techniques, the GP3 of our NA reference strain IAF-Klop was reported to be a non structural and secreted protein from PRRSV infected cells. Even if there is only a sequence identity (homology) of 54% between the GP3 of both strains, three out of four proteomic and bioinformatic models (in silico) suggest that LV GP3 is an extracellular protein. Since the GP3 of a NA reference strain is non structural and secreted from infected cells then what is her function? It is well known that other viral secreted proteins (ex: herpes, pox) possess similarities with cytokines and subsequently modulate the immune reponse of infected hosts. The hypothesis of the present proposal is that GP3 of both genotypes share the same characteristics and that secreted GP3 (sGP3) possesses specific activities in PRRSV infected hosts. To prove this hypothesis, different objectives will be realized like: establishing the LV GP3 intra and extracellular localization in comparison with IAF-Klop GP3; evaluating the effect of sGP3 on freshly isolated porcine immune cells; evaluating the pathogenicity of ORF3 mutated PRRSV (which GP3 secretion is suppress) in infected swines.