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Topic

Intron 5 of Ars2 contains internal ribosomal entry sites that control expression of cytoplasmic ARS2 protein isoforms

Department of Biochemistry and Microbiology

Date & location

• Wednesday, December 18, 2024
• 10:00 A.M.
• Engineering & Computer Science Building, Room 130

Examining Committee

Supervisory Committee

• Dr. Perry Howard, Department of Biochemistry and Microbiology, University of Victoria (Supervisor)
• Dr. Chris Nelson, Department of Biochemistry and Microbiology, UVic (Member)
• Dr. Bob Chow, Department of Biology, UVic (Outside Member)

External Examiner

• Dr. John Taylor, Department of Biology, UVic

Chair of Oral Examination

• Dr. Lucinda Brown, Department of Educational Psychology and Leadership Studies, UVic

Abstract

Ars2 is an essential gene in RNA metabolism that can undergo alternative splicing in which either all or a portion of its highly conserved intron 5 is retained. The retention of this intron 5, while resulting in transcripts with long 5’UTRs and uORFs that are sensitive to nonsense-mediated decay and are suboptimal to cap-dependent translation, generates cytoplasmic protein isoform of ARS2 (ARS2c) that are required for response to arsenic stress. Using a reporter plasmid that can generate circular RNAs, I demonstrated that mouse Ars2 intron 5 contains at least 3 internal ribosomal entry sites (IRESs). The presence of these IRESs within intron 5 may explain the translation of ARS2c, and its upregulation in arsenic stress, which normally result in global attenuation of cap-dependent translation. Structural prediction in combination with mutagenesis indicate that these IRESs are highly structured and form pseudoknots at their 3’ ends which are important for their activity. Additionally, my reporter system also indicated that intron 5 and its splice variants contain regulatory elements that modulate the activity of the IRESs. Taken together, my findings provide mechanistic insights into the translation controls of ARS2c. Given that ARS2c is involved in cellular stress response and is a potential cancer suppressor, this work may aid in the development of novel cancer therapeutic strategies.