SAMHD1 Modulates Early Steps during Human Cytomegalovirus Infection by Limiting NF-κB Activation

Kim, Eui Tae; Roche, Kathryn L.; Kulej, Katarzyna; Spruce, Lynn A.; Seeholzer, Steven H.; Coen, Donald M.; Díaz-Griffero, Felipe; Murphy, Eain A.; Weitzman, Matthew D.

doi:10.1016/j.celrep.2019.06.027

Cited by 47 publications

(69 citation statements)

References 104 publications

(171 reference statements)

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“…It has long been assumed that MIE gene expression that supports reactivation of the viral lytic cycle results from derepression of the MIEP, and changes in transcription factor binding and chromatin have been detected at the MIEP upon reactivation (29)(30)(31)(32)(33)(34)(35). While our data do not preclude a role for the MIEP, iP-derived transcripts are the predominant drivers of viral IE gene re-expression following a reactivation stimulus (Fig.…”

Section: Discussionmentioning

confidence: 51%

Alternative promoters drive human cytomegalovirus reactivation from latency

Collins-McMillen

Rak

Buehler

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Reactivation from latency requires reinitiation of viral gene expression and culminates in the production of infectious progeny. The major immediate early promoter (MIEP) of human cytomegalovirus (HCMV) drives the expression of crucial lytic cycle transactivators but is silenced during latency in hematopoietic progenitor cells (HPCs). Because the MIEP has poor activity in HPCs, it is unclear how viral transactivators are expressed during reactivation. It has been presumed that viral gene expression is reinitiated via de-repression of the MIEP. We demonstrate that immediate early transcripts arising from reactivation originate predominantly from alternative promoters within the canonical major immediate early locus. Disruption of these intronic promoters results in striking defects in re-expression of viral genes and viral genome replication in the THP-1 latency model. Furthermore, we show that these promoters are necessary for efficient reactivation in primary CD34 + HPCs. Our findings shift the paradigm for HCMV reactivation by demonstrating that promoter switching governs reactivation from viral latency in a context-specific manner.human cytomegalovirus | latency | reactivation R eactivation of latent human cytomegalovirus (HCMV) infection poses a life-threatening risk to immunocompromised individuals, such as stem cell or organ transplant recipients (1). While the HCMV replicative cycle has been studied extensively, our understanding of the mechanisms controlling the entry into and exit from latency is far from complete.During productive infection, the HCMV genome is transcribed in a temporal cascade composed of three kinetic classes of gene expression designated as immediate early (IE), early, and late (2). The IE proteins, in particular IE1-72 kilodalton (kDa) and IE2-86 kDa proteins, referred to as IE1 and IE2, play critical roles in initiating the HCMV lytic cycle by transactivating the expression of cellular and viral genes and suppressing the innate immune response (3). During latency, IE gene expression is repressed, resulting in diminished viral gene expression and the absence of productive replication (4). Signals that stimulate reactivation induce IE gene expression to allow reentry into the viral replicative cycle (5), and this de-repression of IE genes is considered a pivotal event controlling the switch between latent and reactivated states.The major immediate early promoter (MIEP) is a powerful promoter in cells permissive for lytic HCMV replication and drives high level expression of mRNAs encoding IE1 (UL123) and IE2 (UL122) (6-9). In cell types that support HCMV latency, however, such as CD34 + human progenitor cells (HPCs) and CD14 + monocytes, MIEP activity is diminished (10-12). Because re-expression of UL122 and UL123 is required for reactivation (13-15), it has been presumed that de-repression of the MIEP is critical to reinitiate the viral lytic cycle. However, the origin of UL123 and UL122 transcripts during HCMV reactivation has not been formally defined. ResultsRe-Expression of UL123 ...

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Section: Discussionmentioning

confidence: 51%

Alternative promoters drive human cytomegalovirus reactivation from latency

Collins-McMillen

Rak

Buehler

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…In this regard, HIV-1 contains the protein of the virus VPX, which induces the degradation of SAMHD1 [15]. In another virus, human CMV, NF-κB activation is blocked during the early steps of infection, thereby, leading to limited SAMHD1 inhibition [16]. Also, in human CMV and herpesvirus, the viral kinases pUL97 and BGLF4 phosphorylate SAMHD1 and inactivate the restriction, respectively [17,18].…”

Section: Introductionmentioning

confidence: 99%

Induction of Samhd1 by interferon gamma and lipopolysaccharide in murine macrophages requires IRF1

et al. 2020

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SAMHD1 is an enzyme with phosphohydrolase activity. Mutations in SAMHD1 have been linked to the development of Aicardi‐Goutières syndrome in humans. This enzyme also has the capacity to restrict HIV virus replication in macrophages. Here, we report that Samhd1 is highly expressed in murine macrophages and is regulated by proinflammatory (IFN‐γ and LPS) but not by anti‐inflammatory (IL‐4 or IL‐10) activators. The induction of Samhd1 follows the pattern of an intermediate gene that requires protein synthesis. In transient transfection experiments using the Samhd1 promoter, we found that a fragment of 27 bps of this gene, falling between −937 and −910 bps relative to the transcription start site, is required for IFN‐γ‐dependent activation. Using EMSAs, we determined that IFN‐γ treatment led to the elimination of a protein complex. Chromatin immunoprecipitation assays and siRNA experiments revealed that IRF1 is required for IFN‐γ‐ or LPS‐induced Samhd1 expression. Therefore, our results indicate that Samhd1 is stimulated by proinflammatory agents IFN‐γ and LPS. Moreover, they reveal that these two agents, via IRF1, eliminate a protein complex that may be related to a repressor, thereby, triggering Samhd1 expression.

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“…Unlike HPV16, the effects of beta-herpesvirus human cytomegalovirus (HCMV) on SAMHD1 protein expression appear to be cell specific: While HCMV infection of THP-1 cells induces SAMHD1 expression in a mechanism independent of viral gene expression [177], protein levels decrease in HCMV+ MDMs through transcriptional repression and proteasome-dependent mechanisms [178]. Despite the differential effect of HCMV on steady-state SAMHD1 levels, the virus consistently induces phosphorylation of T592 through viral CHPK UL97-in conjunction with cellular CDK1-and restricts viral replication in both cell types [179].…”

Section: Samhd1 Restriction Of Dna Virusesmentioning

confidence: 99%

“…This activity is shared by the viral kinase M97 of murine cytomegalovirus (MCMV) [134,180]. SAMHD1 restriction of HCMV does not appear to be a result of its dNTPase activity, rather SAMHD1 prevents the accumulation of NF-κB on the HCMV MIE gene promoter, inhibiting transcriptional activation and suppressing viral replication [177,181]. In addition to phosphorylating SAMHD1 to alleviate its restriction, UL97 phosphorylates a host of other proteins during viral replication.…”

Section: Samhd1 Restriction Of Dna Virusesmentioning

confidence: 99%

SAMHD1 Functions and Human Diseases

Coggins

Mahboubi

Schinazi

et al. 2020

Viruses

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Deoxynucleoside triphosphate (dNTP) molecules are essential for the replication and maintenance of genomic information in both cells and a variety of viral pathogens. While the process of dNTP biosynthesis by cellular enzymes, such as ribonucleotide reductase (RNR) and thymidine kinase (TK), has been extensively investigated, a negative regulatory mechanism of dNTP pools was recently found to involve sterile alpha motif (SAM) domain and histidine-aspartate (HD) domain-containing protein 1, SAMHD1. When active, dNTP triphosphohydrolase activity of SAMHD1 degrades dNTPs into their 2′-deoxynucleoside (dN) and triphosphate subparts, steadily depleting intercellular dNTP pools. The differential expression levels and activation states of SAMHD1 in various cell types contributes to unique dNTP pools that either aid (i.e., dividing T cells) or restrict (i.e., nondividing macrophages) viral replication that consumes cellular dNTPs. Genetic mutations in SAMHD1 induce a rare inflammatory encephalopathy called Aicardi–Goutières syndrome (AGS), which phenotypically resembles viral infection. Recent publications have identified diverse roles for SAMHD1 in double-stranded break repair, genome stability, and the replication stress response through interferon signaling. Finally, a series of SAMHD1 mutations were also reported in various cancer cell types while why SAMHD1 is mutated in these cancer cells remains to investigated. Here, we reviewed a series of studies that have begun illuminating the highly diverse roles of SAMHD1 in virology, immunology, and cancer biology.

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SAMHD1 Modulates Early Steps during Human Cytomegalovirus Infection by Limiting NF-κB Activation

Cited by 47 publications

References 104 publications

Alternative promoters drive human cytomegalovirus reactivation from latency

Alternative promoters drive human cytomegalovirus reactivation from latency

Induction of Samhd1 by interferon gamma and lipopolysaccharide in murine macrophages requires IRF1

SAMHD1 Functions and Human Diseases

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