Evaluating the specificity of flavivirus proteases in Aedes aegypti cells for dengue virus 2-derived cleavage sites

Flaviviruses are a diverse group of RNA viruses known for their significant impact on human health worldwide. We generated a series of reporters that included cleavage sequences from the dengue virus type 2 polyprotein and co-transfected with plasmids encoding various flavivirus proteases into Aedes aegypti cells, followed by fluorescent imaging and western blot analysis for the determination of proteolytic cleavage. Recombinant flavivirus NS2B3 proteases from medically significant and insect-specific flaviviruses were able to process reporters encoding cleavage sequences from the dengue virus type 2 polyprotein in vitro including proteases from dengue virus types 1-4, Zika virus, yellow fever virus, Aedes flavivirus, and cell-fusing agent virus. Reporters were not cleaved when transfected cells were infected with dengue virus type 2. Endoplasmic reticulum tethered reporters were also cleaved by protease alone but not by infectious virus. These results shed light on the ability of multiple flavivirus proteases to cleave sequences derived from outside of their genome and raise new questions concerning the requirements for effective cleavage by flavivirus proteases in trans.