Human cytomegalovirus immediate-early gene expression is restricted by the nuclear domain 10 component Sp100

Nuclear domains 10 (ND10s) are discrete subnuclear structures that contain the three major protein components promyelocytic leukaemia protein (PML), hDaxx and Sp100. Previous studies identified the ND10-components PML and hDaxx as cellular restriction factors that independently counteract human cytomegalovirus (HCMV) infection via the repression of viral immediate-early (IE) gene expression. Consequently, we asked whether Sp100 is likewise involved in this repressive activity. Infection of Sp100 knockdown (kd) cells with HCMV resulted in a significantly increased plaque-forming ability. In addition, ablation of Sp100 led to a considerable increase in the number of IE1-expressing cells, indicating that Sp100 suppresses the initiation of viral gene expression. Next, double-kd cells, lacking either Sp100/hDaxx or Sp100/PML, were generated. Here, infection resulted in an additional enhancement in HCMV replication efficacy compared with the single-kd cells. Thus, our results further strengthen the concept that the three major ND10-components independently contribute to the cellular restriction of HCMV replication.