Browsing by Subject "Cell Transformation, Viral"

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    Analysis of Epstein-Barr virus-regulated host gene expression changes through primary B-cell outgrowth reveals delayed kinetics of latent membrane protein 1-mediated NF-κB activation.
    (Journal of virology, 2012-10) Price, Alexander M; Tourigny, Jason P; Forte, Eleonora; Salinas, Raul E; Dave, Sandeep S; Luftig, Micah A
    Epstein-Barr virus (EBV) is an oncogenic human herpesvirus that dramatically reorganizes host gene expression to immortalize primary B cells. In this study, we analyzed EBV-regulated host gene expression changes following primary B-cell infection, both during initial proliferation and through transformation into lymphoblastoid cell lines (LCLs). While most EBV-regulated mRNAs were changed during the transition from resting, uninfected B cells through initial B-cell proliferation, a substantial number of mRNAs changed uniquely from early proliferation through LCL outgrowth. We identified constitutively and dynamically EBV-regulated biological processes, protein classes, and targets of specific transcription factors. Early after infection, genes associated with proliferation, stress responses, and the p53 pathway were highly enriched. However, the transition from early to long-term outgrowth was characterized by genes involved in the inhibition of apoptosis, the actin cytoskeleton, and NF-κB activity. It was previously thought that the major viral protein responsible for NF-κB activation, latent membrane protein 1 (LMP1), is expressed within 2 days after infection. Our data indicate that while this is true, LCL-level LMP1 expression and NF-κB activity are not evident until 3 weeks after primary B-cell infection. Furthermore, heterologous NF-κB activation during the first week after infection increased the transformation efficiency, while early NF-κB inhibition had no effect on transformation. Rather, inhibition of NF-κB was not toxic to EBV-infected cells until LMP1 levels and NF-κB activity were high. These data collectively highlight the dynamic nature of EBV-regulated host gene expression and support the notion that early EBV-infected proliferating B cells have a fundamentally distinct growth and survival phenotype from that of LCLs.
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    Epstein-Barr virus induces global changes in cellular mRNA isoform usage that are important for the maintenance of latency.
    (Journal of virology, 2013-11) Homa, Nicholas J; Salinas, Raul; Forte, Eleonora; Robinson, Timothy J; Garcia-Blanco, Mariano A; Luftig, Micah A
    Oncogenic viruses promote cell proliferation through the dramatic reorganization of host transcriptomes. In addition to regulating mRNA abundance, changes in mRNA isoform usage can have a profound impact on the protein output of the transcriptome. Using Epstein-Barr virus (EBV) transformation of primary B cells, we have studied the ability of an oncogenic virus to alter the mRNA isoform profile of its host. Using the algorithm called SplicerEX with two complementary Affymetrix microarray platforms, we uncovered 433 mRNA isoform changes regulated by EBV during B-cell transformation. These changes were largely orthogonal with the 2,163 mRNA abundance changes observed during transformation, such that less than one-third of mRNAs changing at the level of isoform also changed in overall abundance. While we observed no preference for a mechanistic class of mRNA isoform change, we detected a significant shortening of 3' untranslated regions and exclusion of cassette exons in EBV-transformed cells relative to uninfected B cells. Gene ontology analysis of the mRNA isoform changes revealed significant enrichment in nucleic acid binding proteins. We validated several of these isoform changes and were intrigued by those in two mRNAs encoding the proteins XBP1 and TCF4, which have both been shown to bind and activate the promoter of the major EBV lytic trans-activator BZLF1. Our studies indicate that EBV latent infection promotes the usage of mRNA isoforms of XBP1 and TCF4 that restrict BZLF1 activation. Therefore, characterization of global changes in mRNA isoform usage during EBV infection identifies a new mechanism for the maintenance of latent infection.
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    Inhibition of Neu-induced mammary carcinogenesis in transgenic mice expressing ERΔ3, a dominant negative estrogen receptor α variant.
    (Hormones & cancer, 2012-12) Davis, Vicki L; Shaikh, Firdos; Gallagher, Katie M; Villegas, Michael; Rea, Sheri L; Cline, J Mark; Hughes, Claude L
    The estrogen receptor α (ERα) splicing variant with an in-frame deletion of exon 3 (ERΔ3) is frequently expressed in the normal breast, but its influence on tumorigenesis has not been explored. In vitro, ERΔ3 has dominant negative activity, suggesting it may suppress estrogen stimulation in the breast. ERΔ3 may inhibit classical signaling on estrogen response element (ERE)-regulated genes as well as activate non-classical pathways at Sp1 and AP-1 sites. Transgenic mice were developed that express mouse ERΔ3 in all tissues examined, including the mammary gland. To investigate if ERΔ3 expression affects tumorigenesis, ERΔ3 mice were crossbred with MMTV-Neu mice. Mammary tumor onset was significantly delayed in ERΔ3/Neu versus MMTV-Neu females and metastatic incidence and burden was significantly reduced. Consequently, ERΔ3 expression suppressed tumor development and metastasis in this aggressive model of HER2/Neu-positive breast cancer. To determine if ER ligands with anticancer activity may augment ERΔ3 protection, the bitransgenic mice were treated with tamoxifen and soy isoflavones starting at age 2 months. Soy protein with isoflavones (181 mg/1,800 kcal) did not affect tumor development in MMTV-Neu or ERΔ3/Neu mice; however, metastatic progression was not inhibited in soy-treated ERΔ3/Neu mice, as it was in untreated ERΔ3/Neu mice. In contrast, tamoxifen (20 mg/1,800 kcal) significantly enhanced tumor prevention in ERΔ3/Neu versus MMTV-Neu mice (98% vs. 81% tumor free). The results in ERΔ3/Neu mice demonstrate that ERΔ3 influences estrogen-dependent mammary carcinogenesis and, thus, may be protective in women expressing ERΔ3 in the breast. However, exposure to different estrogens may augment or block its beneficial effects.