Coordinate Inhibition of Cytokine-mediated Induction of Ferritin H, Manganese Superoxide Dismutase, and Interleukin-6 by the Adenovirus E1A Oncogene

The transcriptome of the adenovirus infected cell

Alternations of cellular gene expression following an adenovirus type 2 infection of human primary cells were studied by using superior sensitive cDNA sequencing. In total, 3791 cellular genes were identified as differentially expressed more than 2-fold. Genes involved in DNA replication, RNA transcription and cell cycle regulation were very abundant among the up-regulated genes. On the other hand, genes involved in various signaling pathways including TGF-β, Rho, G-protein, Map kinase, STAT and NF-κB stood out among the down-regulated genes. Binding sites for E2F, ATF/CREB and AP2 were prevalent in the up-regulated genes, whereas binding sites for SRF and NF-κB were dominant among the down-regulated genes. It is evident that the adenovirus has gained a control of the host cell cycle, growth, immune response and apoptosis at 24 h after infection. However, efforts from host cell to block the cell cycle progression and activate an antiviral response were also observed.

HDAC inhibitor-induced activation of NF-κB prevents apoptotic response of E1A+Ras-transformed cells to proapoptotic stimuli

HDAC inhibitors (HDACIs) are capable of suppressing the cell growth of tumour cells due to the induction of apoptosis and/or cell cycle arrest. This allows of considering HDACIs as promising agents for tumour therapy. The final outcome - apoptotic cell death or cell cycle arrest - depends on the type of tumour and cellular context. In this report, we addressed the issue by analysing effects produced in E1A+Ras-transformed MEF cells by HDAC inhibitors sodium butyrate (NaB), Trichostatin A (TSA) and some others. It has been shown that the HDACIs induced cell cycle arrest in E1A+Ras-transformed cells but not apoptosis. The antiapoptotic effect of HDACIs is likely to be a result of NF-κB-dependent signaling pathway activation. HDACI-induced activation of NF-κB takes place in spite of a deregulated PI3K/Akt pathway in E1A+Ras cells, suggesting an alternative mechanism for the activation of NF-κB based on acetylation. HDACI-dependent activation of NF-κB prevents the induction of apoptosis by cytostatic agent adriamycin and serum deprivation. Accordingly, suppression of NF-κB activity in HDACI-arrested cells by the chemical inhibitor CAPE or RelA-siRNA resulted in the induction of an apoptotic programme. Thus, our findings suggest that the activation of the NF-κB pathway in HDACI-treated E1A+Ras-transformed cells blocks apoptosis and may thereby play a role in triggering the programme of cell cycle arrest and cellular senescence.

Adenovirus E1A regulates lung epithelial ICAM-1 expression by interacting with transcriptional regulators at its promoter

We focused on the regulation of inflammatory mediator expression by adenovirus E1A in lung epithelial cells and the role of this viral protein in the pathogenesis of chronic obstructive pulmonary disease (COPD). We previously reported that E1A, a well-known regulator of host genes, increased ICAM-1 expression in human bronchial epithelial (HBE) and A549 cells in response to LPS stimulation. In this report, we clarified the mechanism of this regulation. We found NF-kappaB translocation to the nucleus after LPS stimulation in both E1A-positive and -negative HBE cells. ICAM-1 promoter reporter constructs revealed that a mutation in the proximal NF-kappaB binding site completely inhibited increased transcription, whereas the mutation in a distal site did not. We analyzed the participation of E1A in transcriptional complex formation at this promoter using chromatin immunoprecipitation. In E1A-positive HBE and A549 cells, LPS stimulation increased ICAM-1 promoter immunoprecipitation by NF-kappaB p65 and p300 but not activator protein-1 antibodies with a concomitant increase by the E1A antibody. No increase was found in E1A-negative cells except in HBE cells with p65 antibody. The association of E1A with the increased promoter immunoprecipitation with p300 was also observed after TNF-alpha stimulation of A549 cells. These results suggest that adenovirus E1A regulates the ICAM-1 promoter through its proximal NF-kappaB binding site, most likely by interacting with the transcriptional complex that forms at this site. E1A regulation of the LPS response may play a role in acute exacerbations as a consequence of bacterial infections in COPD.

Elevated intracellular calcium increases ferritin H expression through an NFAT-independent post-transcriptional mechanism involving mRNA stabilization

An increase in intracellular Ca2+ is one of the initiating events in T-cell activation. A calcium-mediated signalling cascade in T-cells involves activation of calcineurin and the dephosphorylation and translocation of NFAT (nuclear factor of activated T-cells), resulting in the transcriptional activation of target genes such as IL-2 (interleukin-2). In the present study, we found that increased intracellular calcium leads to induction of the antioxidant protein ferritin H. We previously reported that the ferritin H gene is transcriptionally activated under oxidative stress conditions through an ARE (antioxidant-responsive element). The facts that the ferritin H ARE contains a composite AP-1 (activator protein 1) site and that NFAT collaborates with AP-1 transcription factors led us to test whether calcium-activated NFAT is involved in the ferritin H induction through the ARE. Treatment of Jurkat T-cells with the calcium ionophore, ionomycin, increased ferritin H mRNA and protein expression. Although NFAT translocated to the nucleus and bound a consensus NFAT sequence located in the IL-2 promoter after ionomycin treatment, it did not activate ferritin H transcription despite the presence of a putative NFAT-binding sequence in the ferritin H ARE. In addition, the calcineurin inhibitor cyclosporin A treatment blocked ionomycin-mediated NFAT nuclear translocation but failed to abrogate the increase in ferritin H mRNA. Analysis of mRNA stability after actinomycin D treatment revealed that ionomycin prolongs ferritin H mRNA half-life. Taken together, these results suggest that ionomycin-mediated induction of ferritin H may occur in an NFAT-independent manner but through post-transcriptional stabilization of the ferritin H mRNA.