Publikationsdatenbank

Cellular factor ND10 complex is involved in repression of lytic replication of human herpesvirus 6A (2019)

Art

Hochschulschrift

Autor

Sanyal, Anirban (WE 5)

Quelle

Berlin, 2019 — 82 Seiten

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/25660

Kontakt

Institut für Virologie

Robert-von-Ostertag-Str. 7-13
14163 Berlin
+49 30 838 51833
virologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

Human herpesvirus-6 (HHV-6) is a betaherpesvirus that has been classified as two distinct virus species, HHV-6A and HHV-6B, based on the differences in their biological and genetic characteristics. Primary infection with HHV-6B causes a febrile illness in children called roseola infantum (sixth disease), which is occasionally associated with neurological issues like seizures and encephalitis. The clinical aspects and epidemiology associated with HHV-6A infections are inadequately understood. Following primary infection the virus establishes a lifelong persistence in infected individuals, termed as latency. Both HHV-6A and -6B are known to integrate their genome into host telomeres of latently infected cells. When integration of the virus occurs in germ cells it results in individuals that harbor the integrated virus in each and every nucleated cell in their body. This condition is commonly termed as inherited chromosomally integrated HHV-6 (iciHHV-6) and is present in about 1 % of the global human population. Both HHV-6A/B can reactivate from latently infected cells, as well as in iciHHV-6 patients, and is associated with several clinical conditions including encephalitis and graft rejection following transplantation. Human cord blood mononuclear cells (CBMC) and peripheral blood mononuclear cells (PBMC) provide efficient replication of HHV-6A and -6B. Various T-cell lines including JJHan and SupT1 cells are permissive to HHV-6A/B lytic replication as well. It is also interesting to note that the viruses can establish latency in these cell lines; however, it remains unknown how the decision between lytic replication and latency is made. In the target cells, after infection, the virus genome is confronted with the nuclear domain 10 (ND10) complex that possesses antiviral activity against a plethora of viruses. The three major constituents of the ND10 complex are namely, promyelocytic leukemia antigen (PML), speckled protein of 100kDa (Sp100) and human death domain-associated protein 6 (hDaxx). Numerous viruses belonging to the herpesviridae family encode proteins that have been shown to manipulate these components and disrupt the ND10 complex during the establishment of infection. For example, ICP0 of herpes simplex virus 1 (HSV-1) induces degradation of PML and Sp100. Similarly, the viral immediate early protein-1 (IE1) of human cytomegalovirus (HCMV) interacts with PML and induces dissociation of the ND10 complex. Additionally, HCMV pp71 induces degradation of hDaxx, which is an important step for productive HCMV gene expression. Majority of known human herpesviruses have been found to efficiently subvert the ND10 complex to establish a successful lytic infection in the host; however, the role of the ND10 complex in HHV-6 infection remains poorly understood. In this project I investigated the role played by the ND10 protein complex on the event of HHV-6A infection. Firstly, to determine the status of ND10 complex in HHV-6A infected cells I stained and checked for the status of PML (indicative of ND10 complex) in HHV-6A infected JJHan cells. Immunofluorescence studies revealed that ND10 bodies are not dissociated, but their number is reduced in lytically infected cells. To address the role of the ND10 complex, I knocked down the key constituents PML, Sp100 and hDaxx in HHV-6A permissive cells using shRNAs. Clonal cell lines were generated from the ployclonal knock down stock. In the follow up step I used the clonal KD10 knock down cells in an infection assay to determine the effect of the absence of ND10 constituents on viral replication. My data revealed that lytic replication of HHV-6A was significantly enhanced upon knockdown of the ND10 complex. Finally, I also investigated the effect of ND10 complex on suppression of viral gene expression. For this purpose I HHV-6A virus with a GFP tag on the late lytic gene U57 and infected ND10 knockdown cells. The data obtained clearly showed that viral gene expression was more efficient in cells upon knockdown of ND10 complex as compared to the parental cells. Taken altogether, my data provides the unique evidence that unlike other human herpesviruses HHV-6A replication within host cells are suppressed by the ND10 complex. Furthermore HHV-6A gene expression is also silenced because of the presence of the ND10 complex. Also, my study garners evidence of stronger lytic replication of HHV-6A in the absence of the ND10 complex, which provides a strong case for the ND10 complex as a key contributor towards HHV-6A latency.