Cellular and viral factors promoting efficient enterovirus uncoating and replication

Abstract

Enteroviruses are small non-enveloped RNA viruses, which belong to the family of picornaviruses. Although most of the diseases that enteroviruses cause are symptomless or mild, enteroviruses are the most common viruses infecting humans. In addition, enteroviruses can cause more severe diseases such as encephalitis or myocarditis. Despite their prevalence, there are no antivirals on the market against these viruses, and vaccines have been developed only against couple of serotypes. For antiviral development, it is crucial to obtain detailed information about factors that contribute to efficient infection. Thus, this thesis focuses on viral and host cell factors that promote the infection of enterovirus B species after cell entry. In the first study, we characterized a new echovirus 1 particle during infection, likely a novel form of an uncoating intermediate. This particle was more open compared to the native virus, but still contained VP4 protein, and was able to bind to a receptor and cause infection. The second part of the thesis focused on steps after RNA release, namely translation and replication. First, we showed that in addition to viral proteases, cellular calpain proteases can cleave structural proteins from the enteroviral polyprotein, suggesting that calpains might contribute to proteolytic processing during infection. This was shown in an in-vitro study, where calpains released capsid proteins from the P1 precursor. Second, we showed that translation of enteroviral proteins induced the rearrangement of cellular intermediate filament, vimentin. Vimentin cages associated with components of endoplasmic reticulum and Golgi, as well as with replicating viral RNA and non-structural, but not structural proteins. Furthermore, inhibition of vimentin dynamics resulted in lower production of the non-structural compared to structural proteins, indicating that enteroviral proteins can be produced differently, depending on their association with vimentin cages. Keywords: Calpain; enterovirus; polyprotein processing; replication; translation; uncoating; vimentin