Genome-Wide CRISPR-Cas9 Screen Identifies SMCHD1 as a Restriction Factor for Herpesviruses.

Intrinsic immunity is the frontline of host defense against invading pathogens. To combat viral infection, mammalian hosts deploy cell-intrinsic effectors to block viral replication prior to the onset of innate and adaptive immunity. In this study, SMCHD1 is identified as a pivotal cellular factor that restricts Kaposi's sarcoma-associated herpesvirus (KSHV) lytic reactivation through a genome-wide CRISPR-Cas9 knockout screen. Genome-wide chromatin profiling revealed that SMCHD1 associates with the KSHV genome, most prominently the origin of lytic DNA replication (ORI-Lyt). SMCHD1 mutants defective in DNA binding could not bind ORI-Lyt and failed to restrict KSHV lytic replication. Moreover, SMCHD1 functioned as a pan-herpesvirus restriction factor that potently suppressed a wide range of herpesviruses, including alpha, beta, and gamma subfamilies. SMCHD1 deficiency facilitated the replication of a murine herpesvirus in vivo . These findings uncovered SMCHD1 as a restriction factor against herpesviruses, and this could be harnessed for the development of antiviral therapies to limit viral infection. IMPORTANCE Intrinsic immunity represents the frontline of host defense against invading pathogens. However, our understanding of cell-intrinsic antiviral effectors remains limited. In this study, we identified SMCHD1 as a cell-intrinsic restriction factor that controlled KSHV lytic reactivation. Moreover, SMCHD1 restricted the replication of a wide range of herpesviruses by targeting the origins of viral DNA replication (ORIs), and SMCHD1 deficiency facilitated the replication of a murine herpesvirus in vivo . This study helps us to better understand intrinsic antiviral immunity, which may be harnessed to develop new therapeutics for the treatment of herpesvirus infection and the related diseases.