Cathepsin B Protease Facilitates Chikungunya Virus Envelope Protein-Mediated Infection via Endocytosis or Macropinocytosis.

Mai Izumida,Hideki Hayashi,Atsushi Tanaka,Yoshinao Kubo

doi:10.3390/v12070722

Abstract

Chikungunya virus (CHIKV) is an enveloped virus that enters host cells and transits within the endosomes before starting its replication cycle, the precise mechanism of which is yet to be elucidated. Endocytosis and endosome acidification inhibitors inhibit infection by CHIKV, murine leukemia virus (MLV), or SARS-coronavirus, indicating that these viral entries into host cells occur through endosomes and require endosome acidification. Although endosomal cathepsin B protease is necessary for MLV, Ebola virus, and SARS-CoV infections, its role in CHIKV infection is unknown. Our results revealed that endocytosis inhibitors attenuated CHIKV-pseudotyped MLV vector infection in 293T cells but not in TE671 cells. In contrast, macropinocytosis inhibitors attenuated CHIKV-pseudotyped MLV vector infection in TE671 cells but not in 293T cells, suggesting that CHIKV host cell entry occurs via endocytosis or macropinocytosis, depending on the cell lines used. Cathepsin B inhibitor and knockdown by an shRNA suppressed CHIKV-pseudotyped MLV vector infection both in 293T and TE671 cells. These results show that cathepsin B facilitates CHIKV infection regardless of the entry pathway.

Highlights

Human infection by the mosquito-borne chikungunya virus (CHIKV) induces fever frequently accompanied by severe joint pain, muscle pain, headache, nausea, fatigue, and rash [1]
The inoculated cells were stained with X-Gal, and the resultant blue cells were counted to measure the CHIKV-pseudotyped murine leukemia virus (MLV) vector infection. 293T and TE671 cells were used in the subsequent experiments, because the numbers of blue 293T and TE671 cells were much higher than those of the blue HeLa cells (Figure 1A)
The results of this study suggest that endocytosis and macropinocytosis are necessary for the CHIKV-pseudotyped MLV vector infection in 293T and TE671 cells, respectively

Summary

Introduction

Human infection by the mosquito-borne chikungunya virus (CHIKV) induces fever frequently accompanied by severe joint pain, muscle pain, headache, nausea, fatigue, and rash [1]. Chikungunya fever mainly occurs in Africa, and South and Southeast Asia [1]. Chikungunya virus is a member of the genus Alphavirus in the family. Togaviridae and has an envelope membrane, as do HIV, Ebola virus, and severe acute respiratory syndrome coronavirus (SARS-CoV). The molecular mechanism of CHIKV entry into human target cells has not been studied to the same extent as HIV, Ebola virus, and SARS-CoV. The binding of CHIKV to a cognate cell surface receptor initiates CHIKV infection. CHIKV infection can occur in the Viruses 2020, 12, 722; doi:10.3390/v12070722 www.mdpi.com/journal/viruses

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Conclusion