Browsing by Author "Tuohinto, Krista"

Kaposi’s sarcoma herpesvirus (KSHV), also called human herpesvirus 8 (HHV-8), was discovered following the AIDS-epidemic as the causative agent of Kaposi’s sarcoma (KS), an angiogenic endothelial tumor of the skin, and of two rare lymphoproliferative diseases, primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). Infection by KSHV displays two life cycle phases; latent and lytic replication. In latency, the virus stays dormant within the host, expressing only a few genes and no viral particles are produced. Latency is the default mode of infection, however, upon appropriate induction the virus reactivates to express all of its genes and replicate viral DNA during the productive lytic replication, culminating with the release of infectious progeny particles and lysis of the host cells. Virus reactivation from latency to the lytic replication is an essential step in the KS pathogenesis. Upon KSHV infection, endothelial cells (EC) undergo reprogramming towards spindle cell, the principal proliferating cell in advanced KS lesions. The transcription factor prospero related homeobox gene Prox1 has an important role in mediating the effects of KSHV on EC reprogramming, contributing to the KS development. Prox1 is the master regulator of lymphatic endothelial cell fate, and its expression is manipulated during the KSHV infection. However, the role of Prox1 in the KSHV life cycle and lytic reactivation has not been studied. To elucidate the role of Prox1 in KSHV reactivation from latency, the effect of ectopic expression of Prox1 on the lytic gene and protein expression in both latent and reactivated KSHV-infected cells was studied. This led to a significant increase in KSHV lytic gene and protein expression, suggesting Prox1 as a positive regulator of KSHV lytic replication. Moreover, Prox1 wild-type, but not its DNA-binding deficient mutant, could significantly increase the release of infectious virions. To investigate the expression levels of Prox1 during KSHV infection, infection kinetics assay was performed, which showed an increase in the Prox1 levels during acute infection. Intriguingly, this was followed by a progressive decrease in the Prox1 levels as latency was established. In conclusion, the focus of this thesis is to investigate the role of Prox1 in KSHV reactivation, and to provide a deeper insight into the virus reactivation mechanisms that can be utilized for future therapeutic strategies against KSHV-mediated tumorigenesis of KS. Keywords: KSHV, Kaposi’s sarcoma, Prox1, virus reactivation, lytic replication