Deletion of the CTRL2 Insulator in HSV-1 Results in the Decreased Expression of Genes Involved in Axonal Transport and Attenuates Reactivation In Vivo

Abstract

HSV-1 is a human pathogen that establishes a lifelong infection in the host. HSV-1 is transported by retrograde axonal transport to sensory neurons in the peripheral nervous system where latent viral genomes can reactivate. The resulting virus travels via anterograde axonal transport to the periphery and can cause clinical disease. CTCF insulators flank the LAT and IE regions of HSV-1 and during latency and maintain the integrity of transcriptional domains through a myriad of functions, including enhancer-blocking or barrier-insulator functions. Importantly, during reactivation, CTCF protein is evicted from the HSV-1 genome, especially from the CTRL2 insulator. CTRL2 is a functional insulator downstream of the 5′exon region of the LAT, so these results suggest that the disruption of this insulator may be required for efficient HSV-1 reactivation. To further explore this, we used a recombinant virus containing a deletion of the CTRL2 insulator (ΔCTRL2) in a rabbit ocular model of HSV-1 infection and induced reactivation. We show that, in the absence of the CTRL2 insulator, HSV-1 established an equivalent latent infection in rabbits, but those rabbits failed to efficiently reactivate from latency. Furthermore, we found a significant decrease in the expression of the gene Us9-, a gene that codes for a type II membrane protein that has been shown to be required for anterograde transport in neurons. Taken together, these results suggest that the functions of the CTRL2 insulator and Us9 activation in reactivating neurons are intrinsically linked through the regulation of a gene responsible for the axonal transport of HSV-1 to the periphery.

Three-Dimensional Chromatin Structure of the EBV Genome: A Crucial Factor in Viral Infection

“…Furthermore, several studies have revealed that CTCF can regulate viral gene expression in other double-stranded DNA viruses. For instance, in Kaposi’s sarcoma herpesvirus (KSHV) [ 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ], herpes simplex virus (HSV) [ 83 , 84 , 85 , 86 , 87 , 88 , 89 ] and human cytomegalovirus (CMV) [ 90 ], CTCF has been shown to bind to the viral genome and regulate viral gene expression by modulating the accessibility of the viral genome to transcription factors. Finally, it has also been suggested that viruses can modulate CTCF activity to promote viral replication.…”

Immunopathology of herpes simplex virus‐associated neuroinflammation: Unveiling the mysteries

“…Subsequent reactivation triggers anterograde axonal movement of the virus towards the periphery, potentially resulting in clinical disease manifestation. 52 Reactivation of HSV plays a pivotal role in instances of fatal encephalitis within the US. It contributes significantly to recurrent herpetic keratitis, a leading cause of blindness.…”

“…It is within these neurons that latent viral genomes persist. Subsequent reactivation triggers anterograde axonal movement of the virus towards the periphery, potentially resulting in clinical disease manifestation 52 . Reactivation of HSV plays a pivotal role in instances of fatal encephalitis within the US.…”

“…The CTCF protein is displaced in the reactivation process, allowing the LAT enhancer to activate the Us9 promoter. Without the presence of the CTRL2 insulator, the spatial orientation between the LAT and Us9 regions is disrupted, hindering efficient reactivation potentially involving axonal transport mechanisms 52 . Another study unveiled that HSV‐1 infection contributed to the diminution of cell‐cell barrier resistance in human brain microvascular endothelial cells, signifying the compromised integrity of the BBB.…”