Role for Tumor Necrosis Factor Alpha in Murine Cytomegalovirus Transcriptional Reactivation in Latently Infected Lungs

Abstract

Interstitial pneumonia is a major clinical manifestation of primary or recurrent cytomegalovirus (CMV) infection in immunocompromised recipients of a bone marrow transplant. In a murine model, lungs were identified as a prominent site of CMV latency and recurrence. Pulmonary latency of murine CMV is characterized by high viral genome burden and a low incidence of variegated immediate-early (IE) gene expression, reflecting a sporadic activity of the major IE promoters (MIEPs) and enhancer. The enhancer-flanking promoters MIEP1/3 and MIEP2 are switched on and off during latency in a ratio of ϳ2:1. MIEP1/3 latencyassociated activity generates the IE1 transcript of the ie1/3 transcription unit but not the alternative splicing product IE3 that encodes the essential transactivator of early gene expression. Splicing thus appeared to be an important checkpoint for maintenance of latency. In accordance with previous work of others, we show here that signaling by the proinflammatory cytokine tumor necrosis factor alpha (TNF-␣) activates IE1/3 transcription in vivo. As an addition to current knowledge, Poisson distribution analysis revealed an increased incidence of IE1/3 transcriptional events as well as a higher amount of transcripts per event. Notably, TNF-␣ promoted the splicing to IE3 transcripts, but transcription did not proceed to the M55/gB early gene. Moreover, the activated transcriptional state induced by TNF-␣ did not predispose latently infected mice to a higher incidence of virus recurrence after hematoablative treatment. In conclusion, TNF-␣ is an important inductor of IE gene transcriptional reactivation, whereas early genes downstream in the viral replicative cycle appear to be the rate-limiting checkpoint(s) for virus recurrence.

Transplant-induced reactivation of murine cytomegalovirus immediate early gene expression is associated with recruitment of NF-κB and AP-1 to the major immediate early promoter

“…TNF expression is upregulated by allogeneic transplantation (Fig. 6 andHummel et al, 2009, 2001) and TNF is sufficient to activate MCMV IE gene expression and/or reactivation in vivo (Cook et al, 2006;Hummel et al, 2001;Simon et al, 2005). However, our previous studies showed that TNF was not required for reactivation of IE gene expression in response to allogeneic transplantation .…”

“…CMV genomes are heterochromatinized and the IE genes, which are required for lytic replication, are transcriptionally silent in latent infection (Grzimek et al, 2001;Hummel et al, 2001;Kurz et al, 1997Kurz et al, , 1999Liu et al, 2008Liu et al, , 2010Seckert et al, 2013;Simon et al, 2005). Activation of IE gene expression, through recruitment of transcription factors that control MIEP activity and remodelling of viral chromatin, is therefore likely required for reactivation of the virus.…”

“…Murine cytomegalovirus (MCMV) is very similar to HCMV in many important ways, including: (i) ability to establish latency and to reactivate; (ii) hierarchical regulation of viral gene expression; (iii) structure, function and organization of the major immediate early (IE) genes (Keil et al, 1987a, b;Meier & Stinski, 2013;Stenberg et al, 1984); (iv) repression of IE gene expression during latency by heterochromatinization of viral genomes (Grzimek et al, 2001;Hummel & Abecassis, 2002;Hummel et al, 2001;Kurz et al, 1999;Liu et al, 2008;Reeves & Sinclair, 2013;Reeves et al, 2005;Seckert et al, 2013); (v) the presence of similar regulatory elements (e.g. NF-k B, AP-1, Sp1 and CREB/ATF binding sites) in the viral IE enhancers Meier & Stinski, 2013); and (vi) (re)activation of the MIEP and/or IE transcription in response to inflammatory mediators or allogeneic stimulation (Döcke et al, 1994;Fietze et al, 1994;Huang et al, 2012;Hummel & Abecassis, 2002;Hummel et al, 2001;Kew et al, 2014;Lee et al, 2004;Liu et al, 2013;O'Connor & Murphy, 2012;Prösch et al, 1995;Reeves & Compton, 2011;Simon et al, 2005;Stein et al, 1993).…”

Human herpesvirus 6 infection in adult living related liver transplant recipients

“…Numerous in vitro and in vivo studies have elucidated the mechanisms of CMV reactivation and have shown that cytokine production, in particular tumor necrosis factor ␣ (TNF-␣), is involved in reactivation. [27][28][29] Although the molecular mechanism of HHV-6 reactivation remains unclear, we recently showed that interleukin-6 (IL-6) and TNF-␣ might play an important role in HHV-6 reactivation in patients with severe druginduced hypersensitivity syndrome. 30 These findings also suggest that cytokines may play an important role in HHV-6 reactivation in patients after organ transplant.…”

The Impact of Infection on Chronic Allograft Dysfunction and Allograft Survival After Solid Organ Transplantation

“…Different mechanisms of CMV-induced vascular or tissue damage in chronic allograft dysfunction have been proposed. The systemic inflammation induced by CMV replication might alter the state of allograft tolerance in the transplant recipient and subsequently trigger acute allograft rejection mediated by cytokines and other chemical mediators (39,40), which in turn will increase the risk for chronic allograft dysfunction.…”