The field of virology has seen explosive growth in the past few decades. A large amount of effort has gone into successfully delineating virus evolution, genetic diversity, immunology, pathogenesis, structure, vaccine development, viral gene expression and genomic replication strategies. In addition, considerable recent work has been focusing on cellular responses to infection as well as how viruses may induce transformation and oncogenesis. Viruses are obligate intracellular parasites and thus absolutely dependent upon host cells. Not surprisingly, they often cause profound changes in cells, including apoptosis, death and signalling, to name a few perturbations. Thus, the molecular signals for how viruses induce pathophysiological alterations in their hosts have been of growing recent interest. Cellular and organismal responses, such as those induced by virus infection, are invariably mediated by changes in gene and protein expression and modification. Thus, there has been keen interest in understanding how gene and protein expressions and modifications are quantitatively and qualitatively affected by such challenges. From a historical perspective, most early work that examined host protein responses to virus infection employed “biased” approaches, in which investigators targeted a limited number, or only one cellular molecule of interest. Completion of many organisms’ genome sequences has allowed the global “non-biased” simultaneous analysis of the entire repertoire of cellular mRNA species, the transcriptome, by gene micro-arrays. This has provided significant information about how cellular gene expressions are altered by virus-induced perturbations, but has not provided as much information about the encoded proteins. This results for several reasons, including, but not limited to the fact that gene expression levels cannot accurately predict protein expression levels, nor the types and extent of post-translational modifications, many genes encode multiple proteins through splice variants, and protein activity may be affected by a large number of conditions, including phosphorylation. Recent technological and bioinformatic approaches make it now possible to begin to extend similar global analyses to probe the cellular proteome, the repertoire of the actual effector molecules. One general strategy has been to take advantage of improved separations technologies, as well as greatly improved mass spectrometry resolution, to quantitatively or comparatively measure hundreds or thousands of proteins. Proteins from multiple conditions (i.e., mock-infected and infected) may be differentially labelled by various techniques, such as 2D-DIGE, ICAT, iTRAQ, SILAC, with 18O during peptide preparation, and/or by various other methods, and then compared to measure comparative alterations in the levels of proteins induced by the virus infection. Such analyses have also been extended by using “label-free” methods for more efficient multiplexing applications, and/or by examining specific protein modifications. In addition, concerted efforts to raise antibodies against all cellular proteins have resulted in the development of “antibody arrays,” which are also generally used for quantitative or comparative assays. Finally, while assays, such as the above, are generally limited to delineating the absolute amount of specific proteins, newer technologies have been developed that allow the simultaneous probing of hundreds of proteins’ functions. Assays, such as “Activity Based Protein Profiling”, are designed to probe enzymatic activity, with current focus on broad-spectrum proteases and other enzymatic classes. This Research Topic will provide an overview of many of these methods, as well as numerous specific examples of each approach, and how they are used to better delineate the ways viruses affect cellular responses during infection.
