SAMHD1-mediated HIV-1 restriction in cells does not involve ribonuclease activity

Antonucci, Jenna M.; Gelais, Corine St.; Silva, Suresh de; Yount, Jacob S.; Tang, Caroline; Ji, Xiaoyun; Shepard, Caitlin; Xiong, Yong; Kim, Baek; Wu, Li

doi:10.1038/nm.4163

Cited by 84 publications

(89 citation statements)

References 25 publications

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“…SAMHD1 has been reported to possess nuclease activity (Beloglazova et al, 2013; Ryoo et al, 2014), which has since been attributed to persistent co-purifying contaminants (Antonucci et al, 2016; Seamon et al, 2015). Our finding of a rescue of the HR and DNA end resection impairment of SAMHD1 depletion with an active-site mutant of SAMHD1, which abolishes its dNTPase activity and reported nuclease activity, and interaction of SAMHD1 with CtIP/MRE11, which are known nucleases, suggest that SAMHD1’s role in promoting DNA end resection is likely independent of any intrinsic catalytic activity and thus through a scaffold function.…”

Section: Discussionmentioning

confidence: 99%

“…SAMHD1 contains a SAM domain, a protein interaction module (Schultz et al, 1997) and a histidine-aspartic acid (HD) domain, found in a superfamily of proteins with metal dependent phosphohydrolase activity (Aravind and Koonin, 1998). In addition to its well-established dNTPase activity, SAMHD1 binds to ssDNA/RNA (Beloglazova et al, 2013; Goncalves et al, 2012; Seamon et al, 2016; Seamon et al, 2015; Tungler et al, 2013) at its dimer-dimer interface, which sterically blocks tetramerization (Seamon et al, 2016) required for its dNTPase activity (Brandariz-Nunez et al, 2013; Hansen et al, 2014; Ji et al, 2014; Yan et al, 2013; Zhu et al, 2013), and SAMHD1 has been reported to possess DNase/RNase activity (Beloglazova et al, 2013; Ryoo et al, 2014); however, a number of studies indicate that SAMHD1 lacks active-site associated nuclease activity (Antonucci et al, 2016; Goldstone et al, 2011; Goncalves et al, 2012; Seamon et al, 2016; Seamon et al, 2015; Welbourn and Strebel, 2016), which has been attributed to persistent co-purifying contaminants (Antonucci et al, 2016; Seamon et al, 2015). …”

Section: Introductionmentioning

confidence: 99%

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SAMHD1 Promotes DNA End Resection to Facilitate DNA Repair by Homologous Recombination

et al. 2017

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SUMMARY DNA double-strand break (DSB) repair by homologous recombination (HR) is initiated by CtIP/MRN-mediated DNA end resection to maintain genome integrity. SAMHD1 is a dNTP triphosphohydrolase, which restricts HIV-1 infection, and mutations are associated with Aicardi-Goutières syndrome and cancer. We show that SAMHD1 has a dNTPase-independent function in promoting DNA end resection to facilitate DSB repair by HR. SAMHD1 deficiency or Vpx-mediated degradation causes hypersensitivity to DSB-inducing agents, and SAMHD1 is recruited to DSBs. SAMHD1 complexes with CtIP via a conserved carboxyl-terminal domain and recruits CtIP to DSBs to facilitate end resection and HR. Significantly, a cancer-associated mutant with impaired CtIP interaction but not dNTPase-inactive SAMHD1 fails to rescue the end resection impairment of SAMHD1 depletion. Our findings define a dNTPase-independent function for SAMHD1 in HR-mediated DSB repair by facilitating CtIP accrual to promote DNA end resection, providing insight into how SAMHD1 promotes genome integrity and prevents disease, including cancer.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

SAMHD1 Promotes DNA End Resection to Facilitate DNA Repair by Homologous Recombination

et al. 2017

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“…Along these lines, SAMHD1 phosphorylation appears to eliminate its antiviral activity without affecting its dNTPase activity (22,23). However, the relative contribution of each of these two alternative mechanisms in SAMHD1 antiviral activity is controversial (21,58,59). While the ability of SAMHD1 to regulate the size of the dNTP pool is well established in cycling cells, this role is much less clear in noncycling cells, where dNTPs levels are very low.…”

Section: Discussionmentioning

confidence: 99%

“…SAMHD1 can degrade viral nucleic acids through its exonuclease activity (19,20) and deplete the intracellular deoxynucleoside triphosphate (dNTP) pool through its dNTP triphosphatase activity (17). The relative contribution of each activity to the inhibition of HIV replication is the subject of intense debate (21,22). Phosphorylation of threonine 592 has been shown to reduce SAMHD1 antiviral activity while not affecting its dNTPase activity (23).…”

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confidence: 99%

p21 Restricts HIV-1 in Monocyte-Derived Dendritic Cells through the Reduction of Deoxynucleoside Triphosphate Biosynthesis and Regulation of SAMHD1 Antiviral Activity

Valle-Casuso

Allouch

David

et al. 2017

J Virol

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HIV-1 infection of noncycling cells, such as dendritic cells (DCs), is impaired due to limited availability of deoxynucleoside triphosphates (dNTPs), which are needed for HIV-1 reverse transcription. The levels of dNTPs are tightly regulated during the cell cycle and depend on the balance between dNTP biosynthesis and degradation. SAMHD1 potently blocks HIV-1 replication in DCs, although the underlying mechanism is still unclear. SAMHD1 has been reported to be able to degrade dNTPs and viral nucleic acids, which may both hamper HIV-1 reverse transcription. The relative contribution of these activities may differ in cycling and noncycling cells. Here, we show that inhibition of HIV-1 replication in monocyte-derived DCs (MDDCs) is associated with an increased expression of p21cip1/waf, a cell cycle regulator that is involved in the differentiation and maturation of DCs. Induction of p21 in MDDCs decreases the pool of dNTPs and increases the antiviral active isoform of SAMHD1. Although both processes are complementary in inhibiting HIV-1 replication, the antiviral activity of SAMHD1 in our primary cell model appears to be, at least partially, independent of its dNTPase activity. The reduction in the pool of dNTPs in MDDCs appears rather mostly due to a p21-mediated suppression of several enzymes involved in dNTP synthesis (i.e., RNR2, TYMS, and TK-1). These results are important to better understand the interplay between HIV-1 and DCs and may inform the design of new therapeutic approaches to decrease viral dissemination and improve immune responses against HIV-1.IMPORTANCE DCs play a key role in the induction of immune responses against HIV. However, HIV has evolved ways to exploit these cells, facilitating immune evasion and virus dissemination. We have found that the expression of p21, a cyclin-dependent kinase inhibitor involved in cell cycle regulation and monocyte differentiation and maturation, potentially can contribute to the inhibition of HIV-1 replication in monocyte-derived DCs through multiple mechanisms. p21 decreased the size of the intracellular dNTP pool. In parallel, p21 prevented SAMHD1 phosphorylation and promoted SAMHD1 dNTPase-independent antiviral activity. Thus, induction of p21 resulted in conditions that allowed the effective inhibition of HIV-1 replication through complementary mechanisms. Overall, p21 appears to be a key regulator of HIV infection in myeloid cells.

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“…The proposed mechanism of catalysis for SAMHD1 exonuclease activity is a phosphorolytic cleavage of the phosphodiester bond in nucleic acid polymers (91). These findings are widely contested however, as many groups report not being able to detect SAMHD1 nuclease activity or its effect on viral restriction (53, 83, 84, 92, 93). Instead, they propose that co-purification of a contaminating nuclease is responsible for the observed exonuclease activity of SAMHD1.…”

Section: Samhd1 Activation Catalysis and Regulationmentioning

confidence: 99%

SAMHD1: Recurring roles in cell cycle, viral restriction, cancer, and innate immunity

Mauney

Hollis

2018

Autoimmunity

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SAMHD1 is a deoxynucleotide triphosphate (dNTP) hydrolase that plays an important role in the homeostatic balance of cellular dNTPs. Its emerging role as an effector of innate immunity is affirmed by mutations in the SAMHD1 gene that cause the severe autoimmune disease, Aicardi-Goutieres syndrome (AGS) and that are linked to cancer. Additionally, SAMHD1 functions as a restriction factor for retroviruses such as HIV. Here we review the current biochemical and biological properties of the enzyme including its structure, activity, and regulation by post-translational modifications in the context of its cellular function. We outline open questions regarding the biology of SAMHD1 whose answers will be important for understanding its function as a regulator of cell cycle progression, genomic integrity, and in autoimmunity.

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SAMHD1-mediated HIV-1 restriction in cells does not involve ribonuclease activity

Cited by 84 publications

References 25 publications

SAMHD1 Promotes DNA End Resection to Facilitate DNA Repair by Homologous Recombination

SAMHD1 Promotes DNA End Resection to Facilitate DNA Repair by Homologous Recombination

p21 Restricts HIV-1 in Monocyte-Derived Dendritic Cells through the Reduction of Deoxynucleoside Triphosphate Biosynthesis and Regulation of SAMHD1 Antiviral Activity

SAMHD1: Recurring roles in cell cycle, viral restriction, cancer, and innate immunity

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