A viral kinase counteracts in vivo restriction of murine cytomegalovirus by SAMHD1

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The deoxynucleotide triphosphate (dNTP) hydrolase SAMHD1 inhibits retroviruses in non-dividing myeloid cells. Although antiviral activity towards DNA viruses has also been demonstrated, the role of SAMHD1 during cytomegalovirus (CMV) infection remains unclear. To determine the impact of SAMHD1 on the replication of CMV, we used murine CMV (MCMV) to infect a previously established SAMHD1 knockout mouse model and found that SAMHD1 inhibits the replication of MCMV in vivo. By comparing the replication of MCMV in vitro in myeloid cells and fibroblasts from SAMHD1-knockout and control mice, we found that the viral kinase M97 counteracts SAMHD1 after infection by phosphorylating the regulatory residue threonine 603. The phosphorylation of SAMHD1 in infected cells correlated with a reduced level of dNTP hydrolase activity and the loss of viral restriction. Together, we demonstrate that SAMHD1 acts as a restriction factor in vivo and we identify the M97-mediated phosphorylation of SAMHD1 as a previously undescribed viral countermeasure.

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Fig. 1: MCMV replication is enhanced in SAMHD1 KO mice in vivo.
Fig. 2: SAMHD1 does not affect infectivity in vitro and is phosphorylated after MCMV infection.
Fig. 3: WT M97, but not the KD mutant, induces phosphorylation of SAMHD1.
Fig. 4: Increased dNTP levels after infection with MCMV WT but not M97 KD MCMV.
Fig. 5: Replication of M97-defective MCMV is sensitive to SAMHD1-mediated restriction in vitro and in vivo.
Fig. 6: M97-induced phosphorylation at T603 counteracts SAMHD1 restriction.

Data availability

The data that support the findings of the study are available from the corresponding author on reasonable request.


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We thank M. Marschall, M. Mach, B. Kropf and M. Thomas from the Institute of Virology in Erlangen, D. Dudziak and C. Lehmann from the Dermatology Department in Erlangen, and R. Behrendt and D. Lindemann from TU Dresden for their expertise and the sharing of methods and reagents. T.G. and J.D. were funded by the German research foundation (GR3355/3-1) and the J. und F. Marohn Stiftung. J.M. and M.K. were supported by the German research foundation (MI2143/2-1). T.H.W. was supported by grant number SFB643 TP C09. N.F. and D.T. were supported by the LOEWE program from the state of Hesse (Translational Medicine and Pharmacology). Supplementary Fig. 1 is based on artwork provided by servier.com.

Author information

T.G., J.D., T.H.W., M.S. and L.W. designed the project. J.D. generated cell lines, viral amplification, quantification and kinetics. J.D. and A.S. performed the mouse infection experiments. J.D., M.K., J.M. and I.G. analysed SAMHD1 phosphorylation in vitro. B.V., A.H. and S.W. performed the cloning and mouse breeding. J.D., D.T. and N.F. quantified dNTPs by HPLC and M.S., J.D. and T.G. wrote the manuscript.

Correspondence to Thomas Gramberg.

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Supplementary Figs. 1–6, Supplementary references, raw immunoblot data.

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