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Members > Spotlights > Robert Silverman

GVN Center and Member Spotlight

Robert Silverman
Center for Innate Immunity Research (CIIR) at Lerner Research Institute at Cleveland Clinic, Ohio, USA

What are you and your institution currently working on regarding COVID-19?

Cleveland Clinic made a rapid pivot in response to the COVID-19 pandemic with its multidisciplinary team approach dedicated to saving lives through pioneering new treatment and prevention methods. Cleveland Clinic was one of the first organizations to develop a data registry and biobank specific to COVID-19. The registry now holds data from more than 30,000 samples from patients who tested positive for COVID-19 at various Cleveland Clinic locations. The biobank collects biological specimens from patients and links data to clinical outcomes using the electronic medical record (EMR). Researchers from across the Cleveland Clinic enterprise are using the dynamic registry data in more than 140 COVID-19 related research projects in areas such as cancer, pediatrics and intensive care. One of the most notable advances arising from the registry data is the development of a medical risk calculator to predict risk of infection and hospitalization.

Another novel approach to COVID-19 research has been in drug repurposing. With no proven treatment, drug repurposing is one of the quickest ways to identify therapies to control the pandemic. Cleveland Clinic researchers published findings on a network-based prediction model using artificial intelligence to identify targets for drug repurposing in coronavirus and COVID-19. Their approach targets the interaction between human and virus proteins rather than the virus protein itself. Based on their findings, they prioritized 16 drugs and three drug combinations as potential treatments. The American Heart Association is funding teams at 12 institutions across the U.S. to begin fast-tracked studies of the effects of COVID-19 on the body’s cardiovascular and cerebrovascular systems. Cleveland Clinic will serve as the initiative’s COVID-19 Coordinating Center and will collect results from the research projects and coordinate the dissemination of all study findings. Among the members of the GVN Center for Innate Immunity Research, the laboratory of Jae Jung has recently established a ferret model for SARS-CoV-2 infection and transmission that highly recapitulates aspects of the human infection. Using mouse and ferret models, they are focused on developing novel mRNA vaccine and ferritin nanoparticle protein vaccine as well as discovering host factors that play important roles in SARS-CoV-2 lifecycle.

The laboratory of Ganes Sen demonstrated that an interferon-inducible protein, Ifit2, protects mice from a neurotropic coronavirus, MHV-A59, by promoting microglial activation and recruitment of peripheral leukocytes to the brain. The newly established Florida Research and Innovation Center (FRIC) of Cleveland Clinic led by Michaela Gack, located in Port St Lucie, Florida, is studying multiple aspects of the interaction of SARS-CoV-2 with the human host. In particular, current studies are focused on the mechanisms of SARS-CoV-2 restriction by the innate immune response, and also on the strategies that SARS-CoV-2 uses to evade or antagonize antiviral innate immunity. Furthermore, collaborative studies are underway to investigate the efficacy of new antivirals to block SARS-CoV-2 infection.

Please describe your work with double-stranded RNA mediated, innate immune responses.

How well our innate immune system functions in the face of virus countermeasures determines whether or not viral infections are controlled long enough to allow the adaptive immune system to clear the infection. Antiviral innate immunity is often triggered by viral double-stranded (ds) RNA. Single-stranded RNA viruses, including the recently emergent SARS-CoV-2 and other coronaviruses, produce dsRNA as replicative intermediates. There are three principal types of cell sensors for viral dsRNA, RIG-I like receptors (RIG-I, MDA5, LGP2), protein kinase PKR, and 2’,5’-oligoadenylate synthetases (OASs). We principally study the last of these, the OAS-RNase L innate immunity pathway. In essence, IFN types I and III produced in response to virus infections induce a family of OASs (enzymatically competent OAS1,2,3, and OASL which is not an enzyme). OASs 1,2&3 activated by binding dsRNA produce a highly unusual series of short 2’-5’ linked oligoadenylates (2-5A) from ATP. The only known function of 2-5A is that it binds to the latent and nearly ubiquitous endoribonuclease RNase L causing it to dimerize and become active for cleaving viral and cellular single-stranded RNA. These events may lead to apoptosis and thus elimination of the virus-infected cells in some circumstances. This laboratory is on a several decades-long quest to better understand how exactly OASs and RNase L control viral infections, how viruses evade the pathway, and how that knowledge can be translated into novel therapies for viral infections.

In recent years, we have combined forces with coronavirologist Susan Weiss at the University of Pennsylvania. As it happens, some, but not all, coronaviruses and rotaviruses intercept and degrade 2-5A as it is being produced in infected cells, thereby preventing RNase L from controlling the infection. The mouse coronavirus (MHV) NS2 protein and the MERS-CoV protein NS4b both have a phosphodiesterase activity that is remarkably specific for degrading 2’,5’-linked oligoadenylates. However, SARS-CoV-2 lacks a homologous phosphodiesterase and no other RNase L antagonist has been demonstrated in SARS-CoV-2. As a result, SARS-CoV-2 is capable of activating the OAS-RNase L pathway and decreasing viral titers in some types of infected cells, but not in other cell types (PMID: 32995797). Coronavirus dsRNA is recognized by MDA5, and not RIG-1, leading to limited amounts of types I and III IFNs and limited IFN-stimulated gene expression in part due to a conserved coronavirus protein with endoribonuclease activity. Some coronaviruses (for example MERS-CoV and murine coronavirus) are adept at preventing activation of PKR, as well as RNase L. However, SARS-CoV-2 activates PKR as well as RNase L indicating this virus is less able to counteract host response to sensing dsRNA. This difference between MERS-CoV and SARS-CoV-2 correlates with the apparent lack of genes encoding a dsRNA binding protein and an RNase L antagonist in the SARS-CoV-2 genome. SARS-CoV-2 activates both RNase L and PKR pathways even when the MAVS dependent IFN productive pathway is knocked out. Currently, we are working on ways to selectively increase 2-5A levels in virus-infected cells with small molecule drug candidates as a possible avenue towards development of broad-spectrum antiviral agents.

Professional Summary

Dr. Silverman has investigated the role interferons (IFNs) play in protecting the body from viruses and cancer for the past 40 years. IFNs are proteins made by and secreted from host cells in response to the presence of certain pathogens. Dr. Silverman is particularly interested in how the enzyme system OAS-RNase L, which protects higher vertebrates from both RNA and DNA viruses, contributes to this process. As often happens, however, viruses have adapted and evolved to inhibit OAS-RNase L activity. He continues on in his decades-long quest to better understand how exactly RNase L works on a cellular and molecular level. This knowledge may help researchers prevent harmful viruses from evading the protective effects of RNase L, and thereby mitigate viral infections and their serious effects. Recent studies implicate the OAS-RNase L pathway in the anti-tumor cell effects of the DNA demethylating drug, 5-azacytidine (AZA), providing a more comprehensive understanding about how AZA and dsRNA prevent the proliferation of cancer cells. This research offers important insights about how a host antiviral protein can, under some conditions, function against cancer cells.

Overview of the Cleveland Clinic

Cleveland Clinic is a nonprofit multi-specialty academic medical center that integrates clinical and hospital care with research and education. Located in Cleveland, Ohio, it was founded in 1921 by four renowned physicians with a vision of providing outstanding patient care based upon the principles of cooperation, compassion and innovation. Cleveland Clinic has pioneered many medical breakthroughs, including coronary artery bypass surgery and the first face transplant in the United States. U.S. News & World Report consistently names Cleveland Clinic as one of the nation’s best hospitals in its annual “America’s Best Hospitals” survey. In 2018, there were 7.9 million total outpatient visits, 238,000 hospital admissions and observations, and 220,000 surgical cases throughout Cleveland Clinic’s health system. Patients came for treatment from every state and 185 countries. Its research facilities encompass over 700,000 sq ft of laboratory space on campus with nearly 2,000 researchers and support personnel and an annual research budget exceeding $300 million.  Lerner Research Institute (LRI) is home to basic, translational, and clinical research at Cleveland Clinic. With its level of funding from federal and, non-federal sources, the LRI ranks in the top 10 Institutes in the country in terms of research success.  Its 30-year history of groundbreaking advances in antiviral innate immunity research makes Cleveland Clinic an internationally recognized institution in this area of research. These advances include many fundamental discoveries on interferon signal transduction and antiviral pathways. Among the members of the GVN center will be leading investigators in viral-host interactions, encompassing antiviral drug development, immune modulatory therapies, and emerging viral pathogens. The center also includes the recently established Florida Research and Innovation Center (FRIC) in Port Saint Lucie, Florida, dedicated to the advancement of innovative translational research focused on immuno-oncology and infectious diseases.