SAMHD1 is active in cycling cells permissive to HIV-1 infection

SAMHDI is a triphosphohydrolase that restricts HIV-1 by limiting the intracellular dNTP pool required for reverse transcription. Although SAMHDI is expressed and active/unphosphorylated in most cell lines, its restriction activity is thought to be relevant only in non-cycling cells. However, an in depth evaluation of SAMHD1 function and relevance in cycling cells is required. Here, we show that SAMHDI-induced degradation by HIV-2 Vpx affects the dNTP pool and HIV-1 replication capacity in the presence of the 3'-azido-3'-deoxythymidine (AZT) in cycling cells. Similarly, in SAMHD1 knockout cells, HIV-1 showed increased replicative capacity in the presence of nucleoside inhibitors, especially AZT, that was reverted by re-expression of wild type SAMHDI. Sensitivity to non-nucleoside inhibitors (nevirapine and efavirenz) or the integrase inhibitor raltegravir was not affected by SAMHDI. Combination of three mutations (S18A, T21A, T25A) significantly prevented SAMHDI phosphorylation but did not significantly affect HIV-1 replication in the presence of AZT. Our results demonstrate that SAMHDI is active in HIV-1 permissive cells, does not modify susceptibility to HIV-1 infection but strongly affects sensitivity to nucleoside inhibitors. (C) 2017 Elsevier B.V. All rights reserved.