Oncolytic Reovirus Infection Is Facilitated by the Autophagic Machinery

Abstract

Mammalian reovirus is a double-stranded RNA virus that selectively infects and lyses transformed cells, making it an attractive oncolytic agent. Despite clinical evidence for anti-tumor activity, its efficacy as a stand-alone therapy remains to be improved. The success of future trials can be greatly influenced by the identification and the regulation of the cellular pathways that are important for reovirus replication and oncolysis. Here, we demonstrate that reovirus induces autophagy in several cell lines, evident from the formation of Atg5-Atg12 complexes, microtubule-associated protein 1 light chain 3 (LC3) lipidation, p62 degradation, the appearance of acidic vesicular organelles, and LC3 puncta. Furthermore, in electron microscopic images of reovirus-infected cells, autophagosomes were observed without evident association with viral factories. Using UV-inactivated reovirus, we demonstrate that a productive reovirus infection facilitates the induction of autophagy. Importantly, knock-out cell lines for specific autophagy-related genes revealed that the expression of Atg3 and Atg5 but not Atg13 facilitates reovirus replication. These findings highlight a central and Atg13-independent role for the autophagy machinery in facilitating reovirus infection and contribute to a better understanding of reovirus-host interactions.

Reovirus Activated Cell Death Pathways

“…Avian ReoV strains utilize autophagic signaling to increase their own reproduction and dissemination by mechanisms that are as-yet undetermined [ 85 , 101 ]. In agreement with this observation, ablating PI3K or autophagy related lipidation proteins 3 and 5 (ATG3/5) in ReoV infected cancer cells reduces viral replication and the amount of progeny virions produced [ 86 , 102 ]. Together, these results suggest that both avian and mammalian ReoV strains co-opt autophagy to promote their own replication and dissemination, although the method through which this is achieved is still not fully clear.…”

“…ReoV can activate apoptotic pathways within murine and human cell lines in culture, and in the murine intestine, heart, and CNS in vivo [ 15 , 85 , 86 ]. ReoV nucleic acids can trigger both intrinsic and extrinsic pathways of apoptosis by directly activating host RNA-sensing proteins, such as RLRs, leading to activation of the transcription factors NF-κB and/or IRF3, and induction of proapoptotic targets such as Noxa and PUMA.…”

“…For example, inhibition of apoptosis in CNS tissues leads to a significant drop in replication, but a similar trend has not been observed in the intestines, heart, liver, or other tissues from ReoV-infected mice [ 92 , 93 , 95 , 96 ]. Conversely, inhibition of autophagy during infection with avian ReoV was associated with increased progeny in chicken tissues [ 85 , 86 , 101 , 102 ]. Whether autophagy has a similar pro-viral role during mammalian ReoV infections, and the cell types in which this autophagy is important for ReoV replication, remains undefined.…”

Immunostimulatory Profile of Cancer Cell Death by the AdV-Lumc007-Derived Oncolytic Virus ‘GoraVir’ in Cultured Pancreatic Cancer Cells

“…The positive correlation with STING expression regardless of the initiated antiviral responses could indicate that STING is involved in GoraVir infection via a different mechanism. Viruses are known to utilize a broad range of cellular proteins to facilitate viral infection, which in some cases are independent from their cellular function [ 39 , 40 , 41 ]. Interestingly, STING has a non-canonical role in promoting cell death [ 42 ].…”