Current Approaches on Viral Infection: Proteomics and Functional Validations

Zheng, Jie; Tan, Boon Huan; Sugrue, Richard; Tang, Kai

Quantitative proteomic approaches have been frequently utilized to study the relative expression level of viral and cellular proteomes upon virus infection. Precise measurement of expression shift could highlight the groups of significantly up-regulated and downregulated proteins, which may serve as key mediators or regulators involved in virus-hijacked secretory pathways. Therefore, these significantly regulated proteins characterized by quantitative proteomics could be considered as potential biomarkers or drug targets for diagnostic or therapeutic purposes. In one study, a proteomic approach, 2D gel combined with quantitative analysis was performed to unravel the changes in the cellular proteome before and after dengue virus serotype 2 (DEN-2) infection (Kanlaya et al., 2010a) . Sixteen host proteins were found to be up-regulated and twenty two proteins down-regulated. Ubiquitin-activating enzyme E1 (UBE1) was identified as a greatly up-regulated protein and its specific inhibitor, UBE1-41, was selected to explore the effect of UBE1 inhibition on virus propagation and infectivity. The treatment resulted in reduced viral protein synthesis and fivefold decrease in virus release. Therefore the importance of ubiquitin-proteasome pathway to DEN-2 infection could be revealed by specifically counteracting UBE1. Another quantitative www.frontiersin.org proteomic study was designed to illustrate sub-cellular changes upon expression of measles virus nucleoprotein (NP), which is a key mediator involved in cellular apoptosis pathway via triggering reactive oxygen species (ROS) and caspase 3 (Bhaskar et al., 2011) . The inhibition of caspase 3 by ascorbic acid could partially reverse and counteract the NP-induced apoptosis. Furthermore, in order to highlight the essential components responsible for antiviral and cell death signaling pathways of influenza A virus infected macrophages, 2D gel coupled with LC-MS/MS was used to quantitatively analyze the up-regulated or down-regulated host proteins in the cytosolic and mitochondrial proteomes (Ohman et al., 2009) . As a result, cytoskeleton proteins, e.g., actin and tubulin, were significantly up-regulated in the mitochondrial fraction; and deliveries of certain proteins involved in the antiviral machinery from cytosolic to mitochondrial region were clearly observed. Also, drug inhibition of actin networks by cytochalasin D could impair the expression of certain major antiviral proteins, such as interferon (IFN)-β and TNF-α. These indicate that actin could regulate the antiviral and cell death signaling pathways involved in mitochondrial responses. In another study, as Epstein-Barr virus (EBV) plays a role in gastric carcinogenesis, Fukagawa et al. (2008) used 2D gel followed by LC-MS/MS to quantitatively study the differentially expressed proteins in EBV infected carcinoma cells. Heat shock protein 27 was identified as a significantly up-regulated phosphorylated protein upon virus infection. Drug inhibition studies demonstrated that PI3K/Akt pathway was closely related to Hsp27/phosphorylation, as phosphorylation level was reduced upon treatment with PI3K inhibitors (LY294002 and wortmannin). As a result, suppression of PI3K signaling pathway could inhibit hsp27 function in EBV-induced gastric carcinomas.