Impact of human Staufen-1 on the particle production and infectivity of HIV-2

Abstract

According to the World Health Organisation, there are 35 million people currently infected with HIV worldwide. Untreated infection with the virus leads to a decline of the CD4+ cell number and weakening of the immune system, resulting in the development of AIDS (acquired immunodeficiency syndrome). This enables opportunistic infections to arise, which may end in death of the infected person. HIV infections are mostly caused by HIV-1, whereas distribution of HIV-2 is more restricted. Due to the fact that viruses are not able to replicate themselves, they are reliant on the host cell and interact with various cellular factors. The human RNA-binding protein Staufen-1 has previously been reported to interact with various proteins of the retroviruses HIV-1, HTLV-1 and HERV-K, affecting production and infectivity of viral particles. Export of viral RNAs, translation of viral proteins as well as assembly of new virions have been named as potential spots for mediating those effects. Within this thesis, the aim was to investigate the eventual interaction of Staufen-1 and HIV-2, gaining more insights into the impact of Staufen-1 on the retroviral replication cycle. It could be demonstrated that Staufen-1 enhances HIV-2 particle production dose-dependently, while simultaneously impairing the infectious potential of emerging virions. The dsRBD3 domain of Staufen-1 could be determined as the potential domain mediating this effect. Furthermore, downregulation of the expression of endogenous Staufen-1 resulted in impaired particle production. By creating a reporter construct carrying the respective Rev-responsive element (RRE), the Rev/RRE-dependent transport of unspliced RNAs could be investigated, on which Staufen-1 had no influence. As the Rec protein was found to be a major Staufen-1 interacting partner for HERV, the interplay of HIV-2 Rev and Staufen-1 was analyzed more in detail. By means of fluorescence microscopy as well as the generated reporter construct, the function of several HIV-2 Rev mutants was examined, a protein involved in export of unspliced viral RNAs out of the nucleus. In this way, potential functional domains of HIV-2 Rev were investigated, which have not been defined yet. Taken together, an impact of Staufen-1 on HIV-2 could be demonstrated for the first time, resulting in outcomes similar to the ones that have been reported for other retroviruses. It remains to be elucidated at which stage of replication the interaction takes place, whether other proteins are involved and by which means the impact of Staufen-1 is important for the virus and the host cell.