Repressor element-1 silencing transcription factor/neuronal restrictive silencer factor (REST/NRSF) can regulate HSV-1 immediate-early transcription via histone modification.
BACKGROUND
During primary infection of its human host, Herpes Simplex Virus Type-1 (HSV-1) establishes latency in neurons where the viral genome is maintained in a circular form associated with nucleosomes in a chromatin configration. During latency, most viral genes are silenced, although the molecular mechanisms responsible for this are unclear. We hypothesized that neuronal factors repress HSV-1 gene expression during latency. A search of the HSV-1 DNA sequence for potential regulatory elements identified a Repressor Element-1/Neuronal Restrictive Silencer Element (RE-1/NRSE) located between HSV-1 genes ICP22 and ICP4. We predicted that the Repressor Element Silencing Transcription Factor/Neuronal Restrictive Silencer Factor (REST/NRSF) regulates expression of ICP22 and ICP4.


RESULTS
Transient cotransfection indicated that REST/NRSF inhibited the activity of both promoters. In contrast, cotransfection of a mutant form of REST/NRSF encoding only the DNA-binding domain of the protein resulted in less inhibition. Stably transformed cell lines containing episomal reporter plasmids with a chromatin structure showed that REST/NRSF specifically inhibited the ICP4 promoter, but not the ICP22 promoter. REST/NRSF inhibition of the ICP4 promoter was reversed by histone deacetylase (HDAC) inhibitor Trichostatin A (TSA). Additionally, chromatin immuno-precipitation (ChIP) assays indicated that the corepressor CoREST was recruited to the proximity of ICP4 promoter and that acetylation of histone H4 was reduced in the presence of REST/NRSF.


CONCLUSIONS
Since the ICP4 protein is a key transactivator of HSV-1 lytic cycle genes, these results suggest that REST/NRSF may have an important role in the establishment and/or maintenance of HSV-1 gene silencing during latency by targeting ICP4 expression.
Pinnoji
Rajeswara C
RC
Department of Basic Pharmaceutical Sciences, College of Pharmacy, The University of Louisiana at Monroe, Monroe, LA 71209, USA. prajeshwarachary@yahoo.com
Bedadala
Gautam R
GR
George
Beena
B
Holland
Thomas C
TC
Hill
James M
JM
Hsia
Shao-chung V
SC
D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D015967:Gene Expression Regulation, Viral; D017930:Genes, Reporter; D018259:Herpesvirus 1, Human / Q000235:genetics*; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000235:genetics; D012097:Repressor Proteins / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic; D054334:Viral Regulatory and Accessory Proteins; D000099229:RE1-Silencing Transcription Factor
D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D017874:Immediate-Early Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D054334:Viral Regulatory and Accessory Proteins; D000099229:RE1-Silencing Transcription Factor; C057294:ICP22 protein, human herpesvirus 1; C048925:herpes simplex virus, type 1 protein ICP4; C012589:trichostatin A