Regulation of ICP0-Null Mutant Herpes Simplex Virus Type 1 Infection by ND10 Components ATRX and hDaxx

Herpes simplex virus type 1 (HSV-1) immediate-early gene product ICP0 activates lytic infection and relieves cell-mediated repression of viral gene expression. This repression is conferred by preexisting cellular proteins and is commonly referred to as intrinsic antiviral resistance or intrinsic defense. PML and Sp100, two core components of nuclear substructures known as ND10 or PML nuclear bodies, contribute to intrinsic resistance, but it is clear that other proteins must also be involved. We have tested the hypothesis that additional ND10 factors, particularly those that are involved in chromatin remodeling, may have roles in intrinsic resistance against HSV-1 infection. The two ND10 component proteins investigated in this report are ATRX and hDaxx, which are known to interact with each other and comprise components of a repressive chromatin-remodeling complex. We generated stable cell lines in which endogenous ATRX or hDaxx expression is severely suppressed by RNA interference. We found increases in both gene expression and plaque formation induced by ICP0-null mutant HSV-1 in both ATRX-and hDaxx-depleted cells. Reconstitution of wild-type hDaxx expression reversed the effects of hDaxx depletion, but reconstitution with a mutant form of hDaxx unable to interact with ATRX did not. Our results suggest that ATRX and hDaxx act as a complex that contributes to intrinsic antiviral resistance to HSV-1 infection, which is counteracted by ICP0.