ORIGINAL ARTICLE

Cell Research (2007): 546-555
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Early Growth Response gene 1 (Egr-1) regulates HSV-1 ICP4 and ICP22 gene expression

Gautam R Bedadala, Rajeswara C Pinnoji and Shao-Chung V Hsia

Correspondence: Shao-Chung V Hsia Tel: 1-318-342-1747; Fax: 1-318-342-1737 E-mail: hsia@ulm.edu

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The molecular mechanisms mediating herpes simplex virus type 1 (HSV-1) gene silencing during latent infection are not clear. Five copies of early growth response gene 1 (Egr-1) binding elements were identified in the intron of HSV-1 ICP22 (infected cell protein No. 22) gene, leading to the hypothesis that Egr-1 binds to the viral genome and regulates the viral gene expression. Transient co-transfection assays indicated that Egr-1 negatively regulated the transcription of both full-length and intron-removed ICP22 promoters. The same assays also revealed that Egr-1 repressed ICP4 (infected cell protein No. 4) promoter activity in a dose-dependent manner but showed less inhibition when the intron was removed. Histone deacetylation was not involved in this regulation since histone deacetylase inhibitor trichostatin A did not exhibit any effect on Egr-1-mediated repression. Chromatin immunoprecipitation assays showed that Egr-1 reduced the binding of Sp1 to the promoters and that the co-repressor Nab2 (NGFI-A/EGR1-binding protein) was recruited to the proximity of ICP4 in the presence of Egr-1. These results suggested that the multifunctional transcription factor Egr-1 can repress HSV-1 immediate-early gene expression through the recruitment of co-repressor Nab2 and reduction of Sp1 occupancy, and thus may play a critical role in HSV-1 gene silencing during latency.

Cell Research (2007) 17:546–555. doi: 10.1038/cr.2007.44; published online 15 May 2007

Keywords: HSV-1, latency, Egr-1, Sp1, Nab2, transcription regulation