The cytotoxicity of coxsackievirus B3 is associated with a blockage of autophagic flux mediated by reduced syntaxin 17 expression

Abstract

Coxsackievirus B3 (CVB3) is an important human pathogen linked to cardiac arrhythmias and acute heart failure. CVB3 infection has been reported to induce the formation of autophagosomes that support the viral replication in host cells. Interestingly, our study shows that the accumulation of autophagosomes during CVB3 infection is caused by a blockage of autophagosome–lysosome fusion rather than the induction of autophagosome biogenesis. Moreover, CVB3 decreases the transcription and translation of syntaxin 17 (STX17), a SNARE (soluble N-ethylmaleimide-sensitive factor activating protein receptor) protein involved in autophagosome–lysosome fusion. Overexpression of STX17 restored the autophagic flux, alleviated the virus-induced lysosomal dysfunction, and decreased the apoptosis induced by CVB3 infection in HeLa cells. Taken together, our results suggest that CVB3 infection impairs the autophagic flux by blocking autophagosome–lysosome fusion. These findings thus point to potential new therapeutic strategies targeting STX17 or autophagosome–lysosome fusion for treating CVB3-associated diseases.

The interplay of autophagy and enterovirus

“…Though most of the research work we summarized in this review show that enteroviruses, e.g. CVB3 [88][89][90][91][92][93], EV-A71 [83][84][85] and poliovirus, manipulate autophagy network to facilitate viral replication, no direct evidences show that viral RNA replication actually takes place in autophagosome or autolysosome. From our point of view, using dsRNA (replication intermediate) antibody to label replication organelles is more ideal and specific than using viral protein immunostaining.…”

“…However, SQSTM1 was accumulated in the infected cells and large autophagy-related vesicles were formed in the infected cells, suggesting that the late stages of autophagy, either fusion of autophagosome with lysosome or degradation in autolysosome, is blocked in CVB3 infected cells [90]. Likewise, autophagic flux was inhibited in CVB3 infected HEK293 and Hela cells [88,89]. In CVB3 infected cells, GFP and RFP signals were co-localized and accumulated, suggesting that fusion of autophagosome with lysosome is blocked.…”

“…Several research groups reported that CVB3 usurps autophagosome to support its replication both in vivo and in vitro [88][89][90][91][92][93]. CVB3 infection induced the formation of double-membranous autophagosomelike vesicle in infected Hela and HEK293A cells under electron microscopy [91].…”

“…The inhibition of autophagic flux was mediated through the modification of soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) proteins. In addition, the level of STX17 (a SNARE of the autophagosome) was decreased following CVB3 infection and overexpression of STX17 rescued the formation of autolysosome, part of lysosomal function, and reduced cell death associated with CVB3 infection [88]. Furthermore, SNAP29 and Pleckstrin homology domain-containing family M member 1 (PLEKHM1), two important proteins regulating fusion of autophagosome and lysosome, were cleaved by proteinase 3C (a nonstructural protein of CVB3), thereby leading to dysfunction of autolysosome formation and degradation [89].…”

The Intertwined Life Cycles of Enterovirus and Autophagy

“…Using different assays, including non-cleavable SQSTM1/p62, mRFP-GFP-LC3 tandem reporter, and electron microscopy, to evaluate flux, several groups have revealed that autophagosome-lysosome fusion is compromised during CVB3 and EV-D68 infection [59,85,86]. To address the underlying mechanism, the Jackson and Luo Laboratories worked in parallel to study the role of SNARE proteins in EV-D68 and CVB3 infection [65,85,87].…”