Selena M. Sagan
Department of Microbiology & Immunology
Lyman Duff Medical Building
3775 University St., Rm 504
Montreal, QC H3A 2B4
Email: selena [dot] sagan [at] mcgill [dot] ca
Now accepting Graduate Students
MicroRNAs and Viral Infections
Viruses have been demonstrated to alter the expression of human microRNAs, cause specific degradation of microRNAs, and even encode their own, virally-derived microRNAs. These can all aid in maintaining viral latency, evasion of immune responses, and ultimately can dictate the outcomes of viral infections. Conversely, human microRNAs can alter the immune system and directly regulate responses to viral infections. Numerous broadly antiviral microRNAs have now been identified; however, their targets and roles in viral infections remain mysterious. What are the target genes of these microRNAs? How do they influence the viral life cycle? What is their role in modulating the immune response and disease pathogenesis? Can they be targeted for antiviral therapy? The answers to these questions will provide a broader understanding of the role of microRNAs in viral infections, immune responses and disease pathogenesis.
Hepatitis C Virus (HCV) and miR-122
Hepatitis C virus (HCV) is a global health problem, affecting approximately 3% of the world population, including more than 250 000 Canadians. Currently, there is no vaccine available and current treatment protocols have limited efficacy. Thus, there is a pressing need for novel anti-HCV strategies.
MicroRNA-122 (miR-122) is a highly abundant liver-specific microRNA that was demonstrated to have a genetic interaction with two sites within the 5’ non-coding region (NCR) of the HCV genome. This is an unusual microRNA interaction as it promotes viral RNA accumulation both in cell culture and in vivo. Curiously, miR-122 has a minimal affect on viral translation and the rate of RNA synthesis. This suggests that miR-122 plays a protective role in preventing the degradation of the viral RNA. We have demonstrated that miR-122 has more extensive interactions with the HCV genome beyond the seed sequences, involving the 5’ terminus of the viral genome (Machlin ES, Sarnow P, and Sagan SM, PNAS 2011). Binding to the HCV RNA genome in this way creates a 3’ overhang which suggests that miR-122 may prevent recognition of the HCV RNA 5’ terminus by nucleases or enzymes that induce innate immune responses. Interestingly, we have demonstrated that a similar interaction occurs between miR-122 and a related virus, termed GB virus B (GBV-B) in cultured liver cells (Sagan SM, Sarnow P, and Wilson JA, J Virol. 2013). We are currently using novel pull-down and RNA analysis strategies to analyze miR-122 complexes in HCV-infected cells, to determine the host and viral factors involved in, and the mechanism of, this unusual microRNA-target RNA interaction. These studies will help to identify novel host-virus interactions, defining new targets for therapeutic intervention.
Interview with Cozzarelli Prize Winners Erica Machlin Cox and Selena Sagan
Science Sessions Podcasts
Proceedings of the National Academy of Sciences (PNAS)
2011 Cozzarelli Prize Winners
Erica Machlin Cox and Selena Sagan discuss an unusual interaction that protects hepatitis C virus from our body’s defenses.
Dynamic Structure of Viral RNAs
The viral RNA genome of positive-sense RNA viruses is highly complex, as it must serve as a template for translation, replication as well as packaging of the viral genome. As such, viral RNA is a dynamic structure associated with numerous host and viral RNA-binding proteins. Using structural probing strategies, such as Selective 2' Hydroxyl Acylation analyzed by Primer Extension (SHAPE), we are currently analyzing viral RNA structure, in vitro and in vivo in numerous contexts. Combined with pull-down strategies we hope to learn more about RNA binding proteins and RNA structures important for viral RNA translation, replication and packaging.
- Sagan SM, Sarnow P, and Wilson JA. Modulation of GB virus B (GBV-B) RNA abundance by microRNA-122: Dependence on and escape from miR-122 restriction. J Virol. (In Press).
- Machlin ES, Sarnow P, and Sagan SM. Combating Hepatitis C Virus by Targeting MicroRNA-122 Using Locked Nucleic Acids. Curr Gene Ther (2012) 12(4): 301-306.
- Nasheri N, Pezacki JP, and Sagan SM. Design and screening of siRNAs against highly structured RNA targets. Methods Mol Biol (2013) 942: 69-86.
- Machlin ES, Sarnow P, and Sagan SM. Masking the 5’ terminal nucleotides of the hepatitis C virus genome by an unconventional microRNA-target RNA complex. Proc Natl Acad Sci U S A (2011) 108 (8): 3193-3198.
- Sagan SM, Nasheri N, Luebbert C, and Pezacki JP. The efficacy of siRNAs against Hepatitis C virus is strongly influenced by structure and target site accessibility. Chem Biol. (2010) May; 17 (5):515-527.
- Sagan SM and Sarnow P. Plasmacytoid dendritic cells as guardians in hepatitis C virus-infected liver. Proc Natl Acad Sci U S A (2010) Apr; 107 (17): 7625-7626.
- Lyn RL, Kennedy DC, Sagan SM, Blais DR, Rouleau Y, Pegoraro A, Xie XS, Stolow A and Pezacki JP. Direct imaging of the disruption of hepatitis C virus replication complexes by inhibitors of lipid metabolism. Virology (2009) Nov; 394 (1): 130-142.
- Koukiekolo R, Jakubek ZJ, Cheng J, Sagan SM, Pezacki JP. Studies of a viral suppressor of RNA silencing p19-CFP fusion protein: a FRET-based probe for sensing double-stranded fluorophore tagged small RNAs. Biophys Chem. (2009) Aug; 43 (3):166-169.
- Cheng J, Koukiekolo R, Kieliszkiewicz K, Sagan SM, and Pezacki JP. Cysteine residues of Carnation Italian ringspot virus p19 suppressor of RNA silencing maintain global structural integrity and stability for siRNA binding. Biochim. Biophys Acta. (2009) Aug; 1794 (8):1197-1203.
- Pezacki JP, Sagan SM, Tonary AM, Rouleau Y, Belanger S, Supekova L, and Su AI. Transcriptional profiling of the effects of 25-hydroxycholesterol on human hepatocyte metabolism and the antiviral state it conveys against the hepatitis C virus. BMC Chem. Biol. (2009) 16(9):2.
- Davis M, Sagan SM, Pezacki JP, Evans DJ, and Simmonds P. Bioinformatic and Physical Characterisation of Genome-Scale Ordered RNA Structure (GORS) in Mammalian RNA Viruses. J. Virol. (2008) Sep; 82 (23):11824-11836.
- Cheng J, Sagan SM, Jakubek Z, and Pezacki JP. Studies of the Interaction of the Viral Suppressor of RNA silencing Protein p19 with Small RNAs Using Fluorescence Polarization. Biochemistry. (2008) Aug; 47(31):8130-8138.
- Cheng J, Sagan SM, Assem N, Koukiekolo R, Goto NK, and Pezacki JP. Stabilized recombinant suppressors of RNA silencing: Functional effects of linking monomers of Carnation Italian Ringspot virus p19. Biochim. Biophys. Acta. (2007) Dec; 1774 (12):1528-1535.
- Koukiekolo R, Sagan SM, and Pezacki JP. Effects of pH and salt concentration on the siRNA binding actitivy of the RNA silencing suppressor protein p19. FEBS Lett. (2007) Jun; 581 (16):3051-3056.
- Sagan SM, Koukiekolo R, Rodgers E, Goto NK, and Pezacki JP. Inhibition of siRNA binding to a p19 viral suppressor of RNA silencing by cysteine alkylation. Angew. Chem. Int. Ed. Engl. (2007) 46 (12):2005-2009.
- Sagan SM, Rouleau Y, Leggiado C, Supekova L, Schultz PG, Su AI, and Pezacki JP. The Influence of Cholesterol and Lipid Metabolism on Host Cell Structure and Hepatitis C Virus Replication. Biochem. Cell Biol. (2006) Feb; 84 (1):67-69.
- Rakic B, Sagan SM, Noestheden M, Belanger S, Nan X, Evans CL, Xie XS, and Pezacki JP. Peroxisome Proliferator-activated Receptor α/γ Antagonism Inhibits Hepatitis C Virus Replication Through Post-transcriptional Effects. Chem. Biol. (2006) Jan; 13 (1):23-30.