Evgeny Pilipenko, D.Sc.

Picornaviruses and IRES Mediated Translational Control

Research Summary

Our laboratory examines the role of RNA/protein interactions in cell-specific regulation of viral gene expression with a goal of clarifying how these processes affect viral disease.

The outcome of virus infection depends on the availability of both the cognate virus’ receptor(s) on the surface of cells and specific factors in the host milieu required for replication of the virus. All viruses use the cell translational machinery to synthesize their proteins. Most viruses have derived distinct strategies allowing their mRNA(s) to successfully compete with cellular mRNAs for translation initiation factors and the ribosomes. There are two modes of translation initiation in eukaryotic cells: 5’-cap-dependent and cap-independent (also referred to as internal initiation of translation). Internal translation initiation is mediated by a specific cis-element of mRNA, called the Internal Ribosome Entry Site (IRES). Particular host cell proteins bind to the IRES and regulate its activity. Internal translation initiation was originally discovered in picornaviruses and subsequently found in other viruses - some of which are important human pathogens, e.g., hepatitis C virus, human immunodeficiency virus type

We focused our studies on the molecular mechanisms of host cell-specific control of viral RNA translation in picornaviruses, which have a positive stranded RNA genome. The family of Picornaviridae includes six major genera that can be clustered into three groups with respect to their IRES structure: (i) Enteroviruses (e.g. poliovirus) and Rhinoviruses; (ii) Cardioviruses and Aphthoviruses (foot-and-mouth disease viruses) and Parechoviruses; (iii) Hepatoviruses (hepatitis A viruses) [the viruses in parentheses are our current objects of studies]. The picornaviruses exhibit a remarkably varied host range with respect to the organisms as well as tissues that they infect; this tropism is associated with a multitude of pathogenic properties. Such diversity depends not only on the ability of a picornavirus to bind and enter particular cells, but also on host-specific factors that interact with the viral genome, especially those that control the IRES function. IRESes of different viruses require different host cell RNA-binding proteins for their function and the tissue-specific expression of these essential factors may often account for distinct tropisms of the viruses. The mutation(s) of a critical RNA cis-element that interacts with an essential host cell-specific protein can lead to a mutant virus (e.g., a vaccine) that is unable to replicate in its primary target host cell and cause disease; nevertheless, the mutant virus can readily grow in cultured cells and replicate in some host cells in an amount sufficient to induce the immune response after vaccination. Our studies have enabled the identification and functional characterization of several host cell-specific proteins that bind the viral RNA’s cis-elements and are key to the virus-induced disease pathogenesis. Our investigations may identify new strategies that are important in preventing or treating viral diseases. Selected cellular mRNAs (including those that encode oncogenes and cell-cycle proteins) also contain IRESes. The same RNA-binding proteins that control picornavirus’ RNA translation and virus pathogenesis may play a critical role in cellular RNA metabolism and the pathogenesis of non-viral induced disease.

Selected Papers

Pilipenko EV, Pestova TV, Kolupaeva VG, Khitrina EV, Poperechnaya AN, Agol VI, Hellen CUT. (2000). A cell cycle-dependent protein serves as a template-specific translation initiation factor. Genes Dev. 14, 2028-2045.

Pilipenko EV, Viktorova EG, Guest ST, Agol VI, Roos RP. (2001). Cell-specific proteins regulate viral RNA translation and virus-induced disease. EMBO J. 20, 6899-6908.

Guest S, Pilipenko EV, Sharma K, Chumakov K and Roos RP.  (2004).  Molecular mechanisms of attenuation of the Sabin strain of poliovirus 3.  J Virol  78: 11097-11107.

Baugh JM, Pilipenko EV.  (2004).  20S proteasome differentially alters translation of different mRNAs via the cleavage of eIF4F and eIF3.  Mol Cell  16: 575-586.