Proof of concept: Targeted protein degradation of the stress granules component G3BP1 as an antiviral strategy against norovirus infection

Human norovirus (HNoV) is a major cause of gastroenteritis worldwide, for which no antiviral therapies exist to date. Previously, our lab has demonstrated that both HNoV and murine norovirus (MNV1) are highly dependant on the expression of the Ras-GTPase-activating protein-binding protein 1 (G3BP1), a cellular protein mostly involved in the assembly of stress granules. We therefore hypothesize that targeting G3BP1 could be a promising antiviral strategy against noroviruses. Here, we designed a proof-of concept study to test targeted protein degradation as a mechanism to induce the specific proteolysis of G3BP1 via the proteasome. To do so, we generated a cellular platform for the over-expression of G3BP1 fused to the bacterial protein Halotag (HaloG3BP1). First, we showed that MNV1 replication is restored in G3BP1-knockout (ΔG3BP1) cells complemented with HaloG3BP1. We then used a proteolysis-targeting-chimera directed towards the Halotag (HaloPROTAC), to induce the specific degradation of HaloG3BP1. We further demonstrate that proteolysis of G3BP1 reduces MNV1 replication, leading to a lower infectious virus yield and preventing virus-induced cell death. We also confirmed that the mechanism of HaloPROTAC3 is mediated via the recruitment of Cullin2-VHL E3-ubiquitin ligase. Our findings add to the body of evidence supporting that targeting of the cellular protein G3BP1 can be used as an antiviral approach, and validates the use of PROTACs for the efficient and specific degradation of cellular factors as a feasible methodology to combat viral diseases.