Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2010
Publication Date: 11/10/2010
Citation: Gladue, D.P., Holinka-Patterson, L.G., Fernandez-Saniz, I., Prarat, M.V., O'Donnell, V.K., Vepkhvadze, N., Lu, Z., Rogers, K., Risatti, G.R., Borca, M.V. 2010. Effects of the interactions of classical swine fever virus core protein with proteins of SUMOylation pathway on virulence in swine. Virology. 407:129-136. Interpretive Summary: Core is one of the four structural proteins of Classical Swine Fever Virus (CSFV) a virus causing a severe disease in swine. Knowledge of Core function is very limited. We identified two swine proteins that interact with CSFV Core during the virus infection. The sites of the Core protein which actually interact with the host proteins were also identified. CSFV harboring alteration of these Core regions resulted completely attenuated in swine. Therefore CSFV Core protein specifically interacts with swine host protein during the cycle of virus replication and this interaction appears to be critical in the mechanism of virus virulence. These results will be useful in vaccine development against this important disease.
Technical Abstract: The classical swine fever virus (CSFV) nucleocapsid or Core protein serves a protective function for the viral RNA, and acts as a transcriptional regulator. However studies involving the CSFV Core protein have been limited. To gain insight into other functions of the Core protein, particularly into its possible role in virus virulence, we utilized the yeast two-hybrid system to screen a custom swine primary macrophage cDNA library to identify host proteins that physically interact with the viral Core protein. Our studies revealed several proteins as specific binding partners for the Core protein. Two of the identified proteins are involved in the sumoylation pathway and were chosen to be analyzed further: SUMO-1 (small ubiquitin-like modifier) and SUMO-1 conjugating enzyme UBC9. Sumoylation is a reversible post-translational modification that has been shown to have various effects on its protein targets, such as to modulate the function of several transcription factors, protein activation, protein stability, and changes in protein intracellular location. Protein modification by SUMO-1 occurs by covalently binding to specific lysine residues in the target protein. In the CSFV Core protein there are five lysines (K) that are high probability binding sites for sumoylation (positions 179, 180, 220, 221 and 246 of the CSFV Brescia strain polyprotein). Substitutions of those lysines for alanines (K'A) demonstrated that K179, K180, and K221 are critical for SUMO-1 recognition, while residue K220 is critical for UBC9 recognition. CSFV mutants harboring point K'A substitutions in these five lysine residues were developed to assay the importance of sumoylation residues for viral virulence in swine. Remarkably, the ability of introduced substitutions in the Core protein affecting SUMO-1 recognition is closely related with virus virulence in swine suggesting that the ability of CSFV Core to bind host SUMO-1 protein during the infection may play a critical role in virus virulence.