The HUSH-SETDB1-MORC2 epigenetic repressor complex restricts herpesvirus infection in association with PML nuclear bodies

Abstract The establishment of latent herpes simplex virus 1 (HSV-1) infection is controlled by promyelocytic leukemia nuclear bodies (PML NBs). Viral genomes are recruited to PML NBs structures and chromatinized by repressive H3.3K9me3 modified H3.3 histone variant to form viral DNA-containing PML-NBs (vDCP NBs). Exactly how this occurs is unclear. Here we identify an essential role for the HUSH complex and its SETDB1 and MORC2 effectors in the establishment and maintenance of latent herpes simplex virus 1 (HSV-1) infection. We show that the formation of repressive heterochromatin is dependent on HUSH, SETDB1 and MORC2 in vDCP NBs, and depletion of any of these components prior to viral infection decreases H3K9me3 levels over latent/quiescent HSV-1 genomes. Once latency is established, depletion of HUSH, SETDB1, or MORC2 by shRNAs or the HIV-2 Vpx protein, induces the reactivation of HSV-1 in infected primary human fibroblasts as well as human induced pluripotent stem cell-derived sensory neurons (hiPSDN). Our data demonstrate the potent antiviral restriction activity of the HUSH/SETDB1/ MORC2 complex to a non-integrated human herpesvirus, its close association with PML NBs, and introduces a new target for anti-herpesvirus therapy.