Sterile alpha motif (SAM) and histidine-aspartate (HD) domain-containing protein 1 (SAMHD1) acts as a restriction factor for several RNA and DNA viruses by limiting the intracellular pool of deoxynucleoside triphosphates. Here, we investigated the regulation of SAMHD1 expression during human cytomegalovirus (HCMV) infection. SAMHD1 knockdown using shRNA increased the activity of the viral UL99 late gene promoter in human fibroblasts by 7- to 9-fold, confirming its anti-HCMV activity. We also found that the level of SAMHD1 was initially increased by HCMV infection but decreased partly at the protein level at late stages of infection. SAMHD1 loss was not observed with UV-inactivated virus and required viral DNA replication. This reduction of SAMHD1 was effectively blocked by MLN4924, an inhibitor of the Cullin-RING-E3 ligase (CRL) complexes, but not by bafilomycin A1, an inhibitor of vacuolar-type H⁺-ATPase. Indirect immunofluorescence assays further supported the CRL-mediated SAMHD1 loss at late stages of virus infection. Knockdown of CUL2 and to a lesser extent CUL1 using siRNA stabilized SAMHD1 in normal fibroblasts and inhibited SAMHD1 loss during virus infection. Altogether, our results demonstrate that SAMHD1 inhibits the growth of HCMV, but HCMV causes degradation of SAMHD1 at late stages of viral infection through the CRL complexes.

无菌 α 基序 (SAM) 和组氨酸-天冬氨酸 (HD) 结构域蛋白 1 (SAMHD1) 通过限制脱氧核苷三磷酸的细胞内池作为几种 RNA 和 DNA 病毒的限制因子。在这里，我们调查了人类巨细胞病毒 (HCMV) 感染期间 SAMHD1 表达的调节。使用 shRNA 敲除 SAMHD1 使人成纤维细胞中病毒 UL99 晚期基因启动子的活性增加了 7 到 9 倍，证实了其抗 HCMV 活性。我们还发现 SAMHD1 的水平最初因 HCMV 感染而增加，但在感染后期的蛋白质水平部分下降。用紫外线灭活的病毒未观察到 SAMHD1 丢失，需要病毒 DNA 复制。SAMHD1 的这种减少被 Cullin-RING-E3 连接酶 (CRL) 复合物的抑制剂 MLN4924 有效阻断，⁺ -ATP酶。间接免疫荧光测定进一步支持了病毒感染晚期 CRL 介导的 SAMHD1 丢失。使用 siRNA 敲低 CUL2 和在较小程度上敲低 CUL1 可稳定正常成纤维细胞中的 SAMHD1，并抑制病毒感染期间的 SAMHD1 丢失。总之，我们的结果表明 SAMHD1 抑制 HCMV 的生长，但 HCMV 通过 CRL 复合物在病毒感染的晚期导致 SAMHD1 降解。