295 human cell factors that influenza A strains must harness to infect a cell, including the currently circulating swine-origin H1N1 have been identified by investigators at Burnham Institute for Medical Research (Burnham), Mount Sinai School of Medicine (Mount Sinai), the Salk Institute for Biological Studies (Salk) and the Genomics Institute of the Novartis Research Foundation (GNF).
The team also identified small molecule compounds that act on several of these factors and inhibit viral replication, pointing to new ways to treat flu. These findings were published online on December 21 in the journal Nature
Influenza A virus contains only enough genetic information (RNA) to produce 11 proteins and must co-opt host cellular machinery to complete its life cycle. Sumit Chanda, Ph.D., of Burnham, Megan Shaw, Ph.D., of Mount Sinai, John Young, Ph.D., of Salk, Yingyao Zhou, Ph.D., of GNF and others used RNAi screening technology to selectively turn off more than 19,000 human genes to determine which human factors facilitate viral entry, uncoating, nuclear import, viral replication and other necessary functions of the virus.
"Because influenza mutates so readily, it has become a moving target for therapeutic intervention, making it difficult to treat circulating strains, including the H1N1 swine flu," said Dr. Chanda. "As a result, there is now widespread resistance to two classes of antiviral drugs. However, by targeting more stable human host factors, we may be able to develop therapies that prevent or treat a variety of influenza A strains and are more likely to maintain their effectiveness."
"This study has provided us with crucial knowledge of the cellular pathways and factors the influenza virus exploits to replicate" added Dr. Shaw. "Each of these represents an 'Achilles heel'' of the virus and vastly increases the number of potential targets for new influenza antiviral drugs."
The team screened human A549 (lung epithelial) cells infected with a modified influenza virus against the genome-wide siRNA library. Conducting two independent screens, they confirmed that selectively impairing each of 295 cellular genes reduced viral infection, effectively illuminating the path followed by influenza viruses during the infection of a cell. Importantly, they found that inhibiting proteins in known drug target classes, such as kinases, vATPases, and tubulin, impairs influenza growth, suggesting that small molecular weight compounds may be developed as host factor-directed antivirals. Protein interactions dataset analysis confirmed 181 host cellular factors that mediate 4,266 interactions between viral or cellular proteins.
Renate Koenig, Ph.D., of Burnham and Peter Palese, Ph.D., Silke Stertz, Ph.D., and Adolfo Garcia-Sastre, Ph.D., of Mount Sinai also collaborated on this research.
"Trying to identify all the host proteins that are required for the replication of influenza viruses is a wonderful challenge and we have come closer to 'knowing'' all the genes involved," said Dr. Palese.
Dr. Young added, "These findings, combined with those from other RNAi screens, provide a blueprint of the cellular processes that are exploited more generally by viruses, pointing towards development of future broad-spectrum antiviral approaches."
About Burnham Institute for Medical Research
Burnham Institute for Medical Research is dedicated to discovering the fundamental molecular causes of disease and devising the innovative therapies of tomorrow. Burnham, with operations in California and Florida, is one of the fastest-growing research institutes in the country. The institute ranks among the top four institutions nationally for NIH grant funding and among the top organizations worldwide for its research impact. For the past decade (1999-2009), Burnham ranked first worldwide in the fields of biology and biochemistry for the impact of its research publications (defined by citations per publication), according to the Institute for Scientific Information.
Burnham utilizes a unique, collaborative approach to medical research and has established major research programs in cancer, neurodegeneration, diabetes, and infectious, inflammatory, and childhood diseases. The Institute is especially known for its world-class capabilities in stem cell research and drug discovery technologies. Burnham is a nonprofit public benefit corporation.
About The Mount Sinai Medical Center
The Mount Sinai Medical Center encompasses The Mount Sinai Hospital and Mount Sinai School of Medicine. The Mount Sinai Hospital is one of the nation''s oldest, largest and most-respected voluntary hospitals. Founded in 1852, Mount Sinai today is a 1,171-bed tertiary-care teaching facility that is internationally acclaimed for excellence in clinical care. Last year, nearly 50,000 people were treated at Mount Sinai as inpatients, and there were nearly 450,000 outpatient visits to the Medical Center.
Mount Sinai School of Medicine is internationally recognized as a leader in groundbreaking clinical and basic science research, as well as having an innovative approach to medical education. With a faculty of more than 3,400 in 38 clinical and basic science departments and centers, Mount Sinai ranks among the top 20 medical schools in receipt of National Institute of Health (NIH) grants.
About the Salk Institute for Biological Studies
The Salk Institute for Biological Studies is one of the world''s preeminent basic research institutions, where internationally renowned faculty probe fundamental life science questions in a unique, collaborative, and creative environment. Focused on both discovery and mentoring future generations of researchers, Salk scientists make groundbreaking contributions to our understanding of cancer, aging, Alzheimer''s, diabetes, and cardiovascular disorders by studying neuroscience, genetics, cell and plant biology, and related disciplines.
Faculty achievements have been recognized with numerous honors, including Nobel Prizes and memberships in the National Academy of Sciences. Founded in 1960 by polio vaccine pioneer Jonas Salk, M.D., the Institute is an independent nonprofit organization and architectural landmark.
About the Genomics Institute of the Novartis Research Foundation
The Genomics Institute of the Novartis Research Foundation develops and applies integrated state-of-the-art technologies in chemistry, biology, automation, and information sciences in order to pursue new approaches towards the understanding of complex biomedical problems in cancer biology, immunology, neuroscience, and metabolic as well as infectious disease. These technologies cut across the life sciences, and include genomics and proteomics tools, medicinal chemistry, cell-based ultra high throughput screening of genes or compounds, structural genomics, and forward/reverse mammalian genetics. The mission of the Institute is to exploit these technologies to identify new biological processes and understand the underlying mechanisms involved in human disease. These discoveries are being translated into human therapeutics through an internal preclinical drug discovery effort coupled with further developmental activities with Novartis. Founded in 1999, the Institute is funded through the Novartis Research Foundation.