The regulation of cellular microRNAs during KSHV lytic replication

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a human tumour virus and the causative agent of Kaposi’s sarcoma (KS), as well as multiple lymphoproliferative diseases. As is characteristic of all herpesviruses, KSHV can undergo both latent and lytic replication cycles. During latent infection, viral gene expression is limited, enabling persistence of the viral genome. Whereas lytic replication is characterised by the abundant transcription of viral genes, and the production and release of infectious virions. Interestingly, both of these cycles are important for KSHV pathogenesis. Viruses have developed numerous mechanisms to manipulate host mRNA expression. Indeed, the dysregulation of cellular miRNAs has emerged as a common mechanism utilised by viruses to influence the host cell transcriptome during infection. In chapter 3, the differential expression of cellular miRNAs was investigated following KSHV lytic reactivation. Notably miR-142-3p and miR-25-p were found to be downregulated. Importantly, overexpression of these miRNAs had a significant impact on KSHV lytic replication, culminating in a substantial reduction in the production of infectious virions. In Chapter 4, GPRC5A was identified as a direct target of miR-142-3p, with the KSHV�mediated downregulation of miR-142-3p thought to contribute to the upregulation of GPRC5A expression during KSHV lytic replication. Subsequent analysis implicated GPRC5A in the regulation of actin dynamics as well as a potential involvement in lipid raft stability. Both of which may enhance viral egress and dissemination. Finally, in Chapter 5 investigations were undertaken to determine the potential mechanisms involved in the regulation of miR-142-3p expression. Results highlighted ORF50 and ADAR editing as potential factors involved in the downregulation of miR-142-3p following KSHV lytic reactivation. To summarise, this study identifies a number of previously unidentified host cell interactions during KSHV lytic replication, which could prove valuable targets for the development of novel therapeutic approaches.