Abstract

Genomic DNA replication is a universal and essential process for all herpesvirus including human cytomegalovirus (HCMV). HCMV UL70 protein, which is believed to encode the primase activity of the viral DNA replication machinery and is highly conserved among herpesviruses, needs to be localized in the nucleus, the site of viral DNA synthesis. No host factors that facilitate the nuclear import of UL70 have been reported. In this study, we provided the first direct evidence that UL70 specifically interacts with a highly conserved and ubiquitously expressed member of the heat shock protein Hsp40/DNAJ family, DNAJB6, which is expressed as two isoforms, a and b, as a result of alternative splicing. The interaction of UL70 with a common region of DNAJB6a and b was identified by both a two hybrid screen in yeast and coimmunoprecipitation in human cells. In transfected cells, UL70 was primarily co-localized with DNAJB6a in the nuclei and with DNAJB6b in the cytoplasm, respectively. The nuclear import of UL70 was increased in cells in which DNAJB6a was up-regulated or DNAJB6b was down-regulated, and was reduced in cells in which DNAJB6a was down-regulated or DNAJB6b was up-regulated. Furthermore, the level of viral DNA synthesis and progeny production was increased in cells in which DNAJB6a was up-regulated or DNAJB6b was down-regulated, and was reduced in cells in which DNAJB6a was down-regulated or DNAJB6b was up-regulated. Thus, DNAJB6a and b appear to enhance the nuclear import and cytoplasmic accumulation of UL70, respectively. Our results also suggest that the relative expression levels of DNAJB6 isoforms may play a key role in regulating the cellular localization of UL70, leading to modulation of HCMV DNA synthesis and lytic infection.

Highlights

  • Human cytomegalovirus (HCMV), is a member of the herpesvirus family, which includes herpes simplex virus 1 (HSV-1), Epstein Barr virus (EBV), and Kaposi’s sarcoma-associated herpesvirus (KSHV) [1]

  • Little is known about how UL70, which is believed to encode the primase activity of the viral DNA replication machinery and is essential for genomic replication, is imported to the nuclei, the site of viral DNA synthesis

  • We demonstrated that the human cytomegalovirus (HCMV) primase interacts with a highly conserved and ubiquitously expressed chaperone protein DNAJB6 that belongs to the heat shock protein 40 (Hsp40) family

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Summary

Introduction

Human cytomegalovirus (HCMV), is a member of the herpesvirus family, which includes herpes simplex virus 1 (HSV-1), Epstein Barr virus (EBV), and Kaposi’s sarcoma-associated herpesvirus (KSHV) [1]. This virus is the leading viral cause of congenital abnormalities and mental retardation in newborns, and causes significant morbidity and mortality in immunocompromised individuals such as AIDS patients and organ transplant recipients. The hallmarks of HCMV pathogenesis include infection of a wide range of tissues and cells such as neuronal cells, and the establishment of lytic and latent infection in many of these tissues [1,2].

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