Julian R. Smith

Bio: Julian R. Smith is an academic researcher from University of Washington. The author has contributed to research in topics: Innate immune system & Viral replication. The author has an hindex of 3, co-authored 4 publications receiving 105 citations.

Endomembrane targeting of human OAS1 p46 augments antiviral activity.

Abstract: Many host RNA sensors are positioned in the cytosol to detect viral RNA during infection. However, most positive-strand RNA viruses replicate within a modified organelle co-opted from intracellular membranes of the endomembrane system, which shields viral products from cellular innate immune sensors. Targeting innate RNA sensors to the endomembrane system may enhance their ability to sense RNA generated by viruses that use these compartments for replication. Here, we reveal that an isoform of oligoadenylate synthetase 1, OAS1 p46, is prenylated and targeted to the endomembrane system. Membrane localization of OAS1 p46 confers enhanced access to viral replication sites and results in increased antiviral activity against a subset of RNA viruses including flaviviruses, picornaviruses, and SARS-CoV-2. Finally, our human genetic analysis shows that the OAS1 splice-site SNP responsible for production of the OAS1 p46 isoform correlates with protection from severe COVID-19. This study highlights the importance of endomembrane targeting for the antiviral specificity of OAS1 and suggests that early control of SARS-CoV-2 replication through OAS1 p46 is an important determinant of COVID-19 severity.

Endomembrane targeting of human OAS1 p46 augments antiviral activity

Abstract: Many host RNA sensors are positioned in the cytosol to detect viral RNA during infection. However, most positive-strand RNA viruses replicate within a modified organelle co-opted from intracellular membranes of the endomembrane system, which shields viral products from host cell innate immune sensors. Targeting innate RNA sensors to the endomembrane system may enhance their ability to sense viral RNA generated by viruses that use these compartments for replication. Here, we reveal that an isoform of oligoadenylate synthetase 1, OAS1 p46, is prenylated and targeted to the endomembrane system. Membrane localization of OAS1 p46 confers enhanced access to viral replication sites and results in increased antiviral activity against a subset of RNA viruses including flavivirus, picornavirus, and SARS-CoV-2. Finally, our human genetic analysis shows that the OAS1 splice-site SNP responsible for production of the OAS1 p46 isoform strongly associates with COVID-19 severity. This study highlights the importance of endomembrane targeting for the antiviral specificity of OAS1 and suggests early control of SARS-CoV-2 replication through OAS1-p46 is an important determinant of COVID-19 severity.

RNA regulatory mechanisms that control antiviral innate immunity.

Abstract: From the initial sensing of viral nucleotides by pattern recognition receptors, through the induction of type I and III interferons (IFN), upregulation of antiviral effector proteins, and resolution of the inflammatory response, each step of innate immune signaling is under tight control. Though innate immunity is often associated with broad regulation at the level of gene transcription, RNA-centric post-transcriptional processes have emerged as critical mechanisms for ensuring a proper antiviral response. Here, we explore the diverse RNA regulatory mechanisms that modulate the innate antiviral immune response, with a focus on RNA sensing by RIG-I-like receptors (RLR), interferon (IFN) and IFN signaling pathways, viral pathogenesis, and host genetic variation that contributes to these processes. We address the post-transcriptional interactions with RNA-binding proteins, non-coding RNAs, transcript elements, and modifications that control mRNA stability, as well as alternative splicing events that modulate the innate immune antiviral response.

Neuroinvasion of SARS-CoV-2 in human and mouse brain.

Abstract: Although COVID-19 is considered to be primarily a respiratory disease, SARS-CoV-2 affects multiple organ systems including the central nervous system (CNS). Yet, there is no consensus on the consequences of CNS infections. Here, we used three independent approaches to probe the capacity of SARS-CoV-2 to infect the brain. First, using human brain organoids, we observed clear evidence of infection with accompanying metabolic changes in infected and neighboring neurons. However, no evidence for type I interferon responses was detected. We demonstrate that neuronal infection can be prevented by blocking ACE2 with antibodies or by administering cerebrospinal fluid from a COVID-19 patient. Second, using mice overexpressing human ACE2, we demonstrate SARS-CoV-2 neuroinvasion in vivo. Finally, in autopsies from patients who died of COVID-19, we detect SARS-CoV-2 in cortical neurons and note pathological features associated with infection with minimal immune cell infiltrates. These results provide evidence for the neuroinvasive capacity of SARS-CoV-2 and an unexpected consequence of direct infection of neurons by SARS-CoV-2.

Neuroinvasion of SARS-CoV-2 in human and mouse brain

Abstract: Although COVID-19 is considered to be primarily a respiratory disease, SARS-CoV-2 affects multiple organ systems including the central nervous system (CNS) Yet, there is no consensus whether the virus can infect the brain, or what the consequences of CNS infection are Here, we used three independent approaches to probe the capacity of SARS-CoV-2 to infect the brain First, using human brain organoids, we observed clear evidence of infection with accompanying metabolic changes in the infected and neighboring neurons However, no evidence for the type I interferon responses was detected We demonstrate that neuronal infection can be prevented either by blocking ACE2 with antibodies or by administering cerebrospinal fluid from a COVID-19 patient Second, using mice overexpressing human ACE2, we demonstrate in vivo that SARS-CoV-2 neuroinvasion, but not respiratory infection, is associated with mortality Finally, in brain autopsy from patients who died of COVID-19, we detect SARS-CoV-2 in the cortical neurons, and note pathologic features associated with infection with minimal immune cell infiltrates These results provide evidence for the neuroinvasive capacity of SARS-CoV2, and an unexpected consequence of direct infection of neurons by SARS-CoV-2

Intratumoral activation of the necroptotic pathway components RIPK1 and RIPK3 potentiates antitumor immunity

Abstract: Although the signaling events that induce different forms of programmed cell death are well defined, the subsequent immune responses to dying cells in the context of cancer remain relatively unexplored. Necroptosis occurs downstream of the receptor-interacting protein kinases RIPK1 and RIPK3, whose activation leads to lytic cell death accompanied by de novo production of proinflammatory mediators. Here, we show that ectopic introduction of necroptotic cells to the tumor microenvironment promotes BATF3+ cDC1- and CD8+ leukocyte-dependent antitumor immunity accompanied by increased tumor antigen loading by tumor-associated antigen-presenting cells. Furthermore, we report the development of constitutively active forms of the necroptosis-inducing enzyme RIPK3 and show that delivery of a gene encoding this enzyme to tumor cells using adeno-associated viruses induces tumor cell necroptosis, which synergizes with immune checkpoint blockade to promote durable tumor clearance. These findings support a role for RIPK1/RIPK3 activation as a beneficial proximal target in the initiation of tumor immunity. Considering that successful tumor immunotherapy regimens will require the rational application of multiple treatment modalities, we propose that maximizing the immunogenicity of dying cells within the tumor microenvironment through specific activation of the necroptotic pathway represents a beneficial treatment approach that may warrant further clinical development.

Z-nucleic-acid sensing triggers ZBP1-dependent necroptosis and inflammation.

Abstract: The biological function of Z-DNA and Z-RNA, nucleic acid structures with a left-handed double helix, is poorly understood1–3. Z-DNA-binding protein 1 (ZBP1; also known as DAI or DLM-1) is a nucleic acid sensor that contains two Zα domains that bind Z-DNA4,5 and Z-RNA6–8. ZBP1 mediates host defence against some viruses6,7,9–14 by sensing viral nucleic acids6,7,10. RIPK1 deficiency, or mutation of its RIP homotypic interaction motif (RHIM), triggers ZBP1-dependent necroptosis and inflammation in mice15,16. However, the mechanisms that induce ZBP1 activation in the absence of viral infection remain unknown. Here we show that Zα-dependent sensing of endogenous ligands induces ZBP1-mediated perinatal lethality in mice expressing RIPK1 with mutated RHIM (Ripk1mR/mR), skin inflammation in mice with epidermis-specific RIPK1 deficiency (RIPK1E-KO) and colitis in mice with intestinal epithelial-specific FADD deficiency (FADDIEC-KO). Consistently, functional Zα domains were required for ZBP1-induced necroptosis in fibroblasts that were treated with caspase inhibitors or express RIPK1 with mutated RHIM. Inhibition of nuclear export triggered the Zα-dependent activation of RIPK3 in the nucleus resulting in cell death, which suggests that ZBP1 may recognize nuclear Z-form nucleic acids. We found that ZBP1 constitutively bound cellular double-stranded RNA in a Zα-dependent manner. Complementary reads derived from endogenous retroelements were detected in epidermal RNA, which suggests that double-stranded RNA derived from these retroelements may act as a Zα-domain ligand that triggers the activation of ZBP1. Collectively, our results provide evidence that the sensing of endogenous Z-form nucleic acids by ZBP1 triggers RIPK3-dependent necroptosis and inflammation, which could underlie the development of chronic inflammatory conditions—particularly in individuals with mutations in RIPK1 and CASP817–20. Analyses of mouse models of inflammation suggest some chronic inflammatory conditions may result from Z-DNA-binding protein 1 sensing endogenous Z-form nucleic acids—such as those of endogenous retroelements—through its Zα domains.

Neuroinvasive potential of SARS-CoV-2 revealed in a human brain organoid model

Abstract: Although COVID-19 is considered to be primarily a respiratory disease, SARS-CoV-2 affects multiple organ systems including the central nervous system (CNS). Reports indicate that 30-60% of patients with COVID-19 suffer from CNS symptoms. Yet, there is no consensus whether the virus can infect the brain, or what the consequences of infection are. Following SARS-CoV-2 infection of human brain organoids, clear evidence of infection was observed, with accompanying metabolic changes in the infected and neighboring neurons. Further, no evidence for the type I interferon responses was detected. We demonstrate that neuronal infection can be prevented either by blocking ACE2 with antibodies or by administering cerebrospinal fluid from a COVID-19 patient. Finally, using mice overexpressing human ACE2, we demonstrate in vivo that SARS-CoV-2 neuroinvasion, but not respiratory infection, is associated with mortality. These results provide evidence for the neuroinvasive capacity of SARS-CoV2, and an unexpected consequence of direct infection of neurons by SARS-CoV2.