This document summarizes research on the protein SAMHD1 and its role in restricting HIV-1 infection. It finds that SAMHD1 is an interferon-induced factor in macrophages and dendritic cells that is degraded by the HIV-2 protein Vpx, allowing infection. Silencing SAMHD1 in dendritic cells through RNA interference increased their susceptibility to HIV-1 infection. Therefore, SAMHD1 acts as an innate immune restriction factor that HIV-1 has not yet evolved to counteract, limiting its ability to productively infect dendritic cells.

1. HIV1- identification of the specific restriction factor SAMHD1 Monsef Benkirane Institut de Génétique Humaine Montpellier CEA CHRU CNRS CPU INRA INRIA INSERM INSTITUT PASTEUR IRD

2. Dendritic cells are refractory to HIV-1 infection Does HIV-1 escapes innate immune recognition by avoiding productive infection of Dendritic cells? X

3. > Initially isolated as an IFN  -induced factor in macrophages and dendritic cells > Like for TREX1 and RNASEH2, mutations in SAMHD1 results in Aicardi Goutière Syndrome AGS AGS is a rare genetic disorder that mimics symptoms from a congenital infection AGS is associated with an increased production of IFN α Purification of Vpx-associated proteins SAM domain and HD domain 1 Protein-Protein interaction domain SAM HD Putative hydrolase domain 45 110 164 319 626 1 Missing in isoform 2 113-126

4. Vpx interacts and induces proteasomal degradation of SAMHD1 SAMHD1 expression correlates with HIV-1 susceptibility F/H-Vpx: SAMHD1 Tubulin + F/H-Vpx WCE DDB1 - R.S.I. 1 0.05 0.7 SAMHD1 Tubulin DDB1 Mg132: - + - VLP-Vpx: + + - shRNA Scr (4) Fold increase Vpx/no Vpx N.I. HIV-LUC-G shRNA Scr (3) (4) Fold Increase x12 x4 Silencing N.I. HIV-LUC-G

5. SAMHD1 restricts HIV-1 infection of Dendritic cells Silencing of SAMHD1 in MDDCs Infection of silenced MDDCs with LV-GFP Infection of silenced MDDCs with HIV-G Dynamin-2 siRNA: - Scr Dyn2 Actin 16 4 0.4 62 22 0.1 65 26 0.2 21 4 0.1 GFP FSC Scr Dyn2 SAMHD1-1 SAMHD1-2 siRNA: N.I. LV GFP 5ng LV GFP 50ng 1 2 48 hr 96 hr SAMHD1 DDB1 Tubulin siRNA: - Scr 1 2 Scr 1 2 HD2 siRNA Fold increase (p24+ cells) Scr 1 2 HD4 0 10 20 30 40

6. The big picture Would decreasing Samhd1 levels allow for better immune control of HIV-1 infection?

8. Many thanks to: LAGUETTE Nadine CHABLE-BESSIA Christine SOBHIAN Bijan RINGEARD Mathieu YATIM Ahmad SCHWARTZ Olivier CASARTELLI Nicoletta EMILIANI Stéphane SEGERAL Emmanuel