Human Cytomegalovirus Induces the Interferon Response via the DNA Sensor ZBP1

Abstract

Human cytomegalovirus (HCMV) is a member of the betaherpesvirus family that, unlike other herpesviruses, triggers a strong innate immune response in infected cells that includes transcription of the beta interferon gene via activation of interferon regulatory factor 3 (IRF3). IRF3 activation requires signaling from pattern recognition receptors that is initiated by their interaction with specific pathogen-associated molecules. However, while IRF3-activating pathways are increasingly well characterized, the cellular molecules involved in HCMV-mediated IRF3-dependent beta interferon transcription are virtually unknown. We undertook a systematic examination of new and established IRF3-terminal pathway components to identify those that are essential to HCMV-triggered IRF3 activation. We show here that IRF3 activation induced by HCMV infection involves the newly identified protein STING but, in contrast to infections with other herpesviruses, occurs independently of the adaptor molecule IPS-1. We also show that the protein DDX3 contributes to HCMVtriggered expression of beta interferon. Moreover, we identify Z-DNA binding protein 1 (ZBP1) as being essential for IRF3 activation and interferon beta expression triggered by HCMV, as well as being sufficient to enhance HCMV-stimulated beta interferon transcription and secretion. ZBP1 transcription was also found to be induced following exposure to HCMV in a JAK/STAT-dependent manner, thus perhaps also contributing to a positive feedback signal. Finally, we show that constitutive overexpression of ZBP1 inhibits HCMV replication. ZBP1 was recently identified as a cytosolic pattern recognition receptor of double-stranded DNA, and thus, we propose a model for HCMV-mediated IRF3 activation that involves HCMV-associated DNA as the principal innate immune-activating pathogen-associated molecular pattern.

Role of nucleotide-binding oligomerization domain 1 (NOD1) and its variants in human cytomegalovirus control in vitro and in vivo

“…The innate immune response to HCMV involves an orchestrated system composed of multiple receptors residing in different cellular compartments (1,4,7,29). Characterizing of these receptors and understanding their function and networking, as well as strategies used by HCMV to counteract their activities, are of paramount importance for HCMV control.…”

“…The activity of the promyeolcytic leukemia protein, a regulator of type I IFN response, is counteracted by HCMV-encoded immediate early 1 protein (IE1) (6). A cytoplasmic dsDNA sensor, ZBP1, activates IRF3 on infection, and its overexpression inhibits HCMV replication (7). IFN-inducible protein IFI16 modestly inhibits HCMV by blocking Sp1-mediated transcription of HCMV-encoded UL54 and UL44, which are involved in viral DNA synthesis (8).…”

Pattern Recognition Receptor–Initiated Innate Antiviral Responses in Mouse Epididymal Epithelial Cells

“…DAI is required for HSV-1-induced IFN production in mouse microglial cells, astrocytes, and fibroblast line L929 (10,45). Human foreskin fibroblasts also require DAI for IFN production in response to CMV infection (46). In contrast, DAI is dispensable for the DNA-triggered IFN production in mouse embryo fibroblasts and dendritic cells (44).…”

Activation of host pattern recognition receptors by viruses

“…DAI has now been show to be important for the antiviral immune response to Human cytomegalovirus (HCMV). It was observed that DAI was essential for IRF3 activation and IFNβ expression triggered by HCMV, and that overexpression of DAI could inhibit replication of HCMV [36]. From this work, the authors suggested that DAI is the principal PRR for the IFNβ response to HCMV infection.…”

“…Although novel downstream signalling components involved in DNA sensing pathways, such as DDX3 [34][35][36] and STING [37], continue to be identified, and although high mobility group proteins have recently been implicated in delivering nucleic acid to PRRs for detection [38], identification of cytoplasmic DNA PRRs (that could bind DNA and transmit a signal to TBK1) remains elusive.…”