Human Rhinovirus 3C protease cleaves RIPK1, concurrent with caspase 8 activation

Abstract

Human Rhinovirus (HRV) is a pathogen of significant medical importance, being a major cause of upper respiratory tract infections (common colds) as well as causing the majority of virus-induced asthma exacerbations. We investigated whether HRV could modulate apoptosis, an innate antiviral response. Apoptotic signals are generated either extrinsically or intrinsically and are propagated via caspase cascades that lead to cell death, reducing viral replication, which relies on cellular machinery. Using HRV16 infected cells, in combination with chemical inducers and inhibitors of extrinsic apoptosis we show that HRV16 3C protease cleaves a key intermediate in extrinsic apoptosis. Receptor-interacting protein kinase-1 (RIPK1), an extrinsic apoptosis adaptor protein, was cleaved by caspase 8, as expected, during chemical induction of apoptosis. RIPK1 was cleaved in HRV infection albeit at a different site. Caspase 8 activation, which is associated with extrinsic apoptosis, was concurrent with HRV 3C protease mediated cleavage of RIPK1, and potentially increased the accessibility of the HRV 3C cleavage site within RIPK1 in-vitro. The caspase 8 mediated RIPK1 cleavage product has a proapoptotic function, and further cleavage of this pro-apoptotic cleavage product by HRV 3C may provide a mechanism by which HRV limits apoptosis.Human Rhinovirus (HRV) is a small virus with a single stranded, positive sense RNA genome that belongs to the Picornaviridae family 1,2 . HRV is the main viral causative agent of the common cold, and the major viral cause of asthma exacerbations 3,4 . The HRV genome encodes structural and functional proteins, of which three proteases (2A, 3CD and 3C) enable viral polyprotein maturation 5 and have been shown to cleave host proteins. The cleavage of translation machinery 5 , transcription factors 6 and nucleoporins 7,8 contributes to host cell shutoff, leading to upregulation of viral translation and transcription. In response to viral infection, the host cell can undergo apoptosis, a method of controlled cell suicide that does not provoke an inflammatory response 9,10 . As viruses rely on host cellular proteins such as translation machinery for replication, initiating cell death would ultimately inhibit viral replication and disrupt the infection cycle 11 . HRV, like other Picornaviridae, is thought to be capable of regulating the apoptotic process through the activity of its proteases towards cellular apoptotic factors 12,13 . The delay or inhibition of apoptosis would allow optimal viral replication and subsequently optimal release and infection.Extrinsic apoptosis is induced within the cell in response to external harmful stimuli and is dependent on the activation of caspase 8 14,15 . Caspase 8 is recruited to the cytoplasmic portion of death receptors that have formed complexes with other death inducing adaptor proteins such as Fas-Associated protein with Death Domain (FADD), Tumor necrosis factor receptor type 1-associated Death Domain protein (TRADD) 14,16 and Receptor-interacting protein kina...

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A Single Point Mutation in the Rhinovirus 2B Protein Reduces the Requirement for Phosphatidylinositol 4-Kinase Class III Beta in Viral Replication

“…The replication of plus-sense RNA viruses in the cytoplasm occurs in close association with membranes of the secretory or the endocytic pathways (reviewed in references 9 and 10-12). Picornavirus infections suppress the early onset of apoptosis and execute viral necrosis (13,14). They remodel cytoplasmic membranes, which involves host protein recruitment to membranes, synthesis and modification of lipids, and alterations in membrane curvature, flux, and traffic.…”

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