Project description:A human embryonic fibroblast cell line was synchronously infected with poliovirus in the absence or presence of interferon-α, or with vacciniavirus, a virus that is not inhibited by interferon. The titers were sufficient to yield productive infection in a majority of the cells. The cells were harvested in triplicate at various time-points, and the transcriptosome compared with mock infected cells using oligo-based 35 k microarrays. The project had two purposes: to characterize the cellular response and to look for candidate genes involved in viral defense. The changes in gene expression due to vaccinia virus did not correspond to those caused by poliovirus. More surprisingly, neither did the changes when comparing 8 h and 16 h of poliovirus infection. However, a large proportion of the genes up-regulated by interferon-α were also up-regulated by poliovirus, both at 8 h and 16 h. Interferon-α inhibited poliovirus replication, thus the observations suggest that the cells do launch an antiviral response to poliovirus. Moreover, as interferon genes were not induced, the data indicate that several of the relevant genes can be activated in an interferon independent manner. Further analyses of the data led to a list of candidate antiviral genes. Functional information was limited, or absent, for most of these genes. Keywords: Poliovirus; Vacciniavirus; Interferon; Microarray; Gene expression; Defense genes
Project description:Although most eukaryotic mRNAs need a functional cap binding complex eIF4F for efficient 5' end- dependent scanning to initiate translation, picornaviral, hepatitis C viral, and a few cellular RNAs have been shown to be translated by internal ribosome entry, a mechanism that can operate in the presence of low levels of functional eIF4F. To identify cellular mRNAs that can be translated when eIF4F is depleted or in low abundance and that, therefore, may contain internal ribosome entry sites, mRNAs that remained associated with polysomes were isolated from human cells after infection with poliovirus and were identified by using a cDNA microarray. Approximately 200 of the 7000 mRNAs analyzed remained associated with polysomes under these conditions. Among the gene products encoded by these polysome-associated mRNAs were immediate-early transcription factors, kinases, and phosphatases of the mitogen-activated protein kinase pathways and several protooncogenes, including c-myc and Pim-1. In addition, the mRNA encoding Cyr61, a secreted factor that can promote angiogenesis and tumor growth, was selectively mobilized into polysomes when eIF4F concentrations were reduced, although its overall abundance changed only slightly. Subsequent tests confirmed the presence of internal ribosome entry sites in the 5' noncoding regions of both Cyr61 and Pim-1 mRNAs. Overall, this study suggests that diverse mRNAs whose gene products have been implicated in a variety of stress responses, including inflammation, angiogenesis, and the response to serum, can use translational initiation mechanisms that require little or no intact cap binding protein complex eIF4F.