News & Events

When

Date - February 8, 2023
1:00 pm - 2:00 pm

What

Ph.D. Defense
Department of Chemistry & Biochemistry
UNC Greensboro
Taylor Research Group

Title: “Disruption of host selenobiology by SARS-CoV-2 and Ebolavirus via RNA:RNA antisense interactions”

Abstract:

Selenium (Se) is an essential, but often overlooked, element in maintaining the health of our biological systems. Occupying the redox center of different selenoproteins like thioredoxin reductase or glutathione peroxidase as selenocysteine allows Se to perform various unique biological functions, e.g., redox regulation and antioxidant defense. The synthesis of selenoproteins involves the reprogramming of a UGA stop codon to allow the recruitment of a selenocysteine t-RNA. This occurs during translation, using a unique RNA structure called a SECIS (selenocysteine insertion sequence) element. The SECIS element can be located within the mRNA being translated, but can also be hijacked from a second RNA molecule through antisense tethering. This tethering can also facilitate another translation event in the form of ribosomal frameshifting which allows genes to encode for multiple proteins by overlapping reading frames. Our research group has previously identified such antisense tethering sites in several pathogenic RNA viruses, including ebolavirus (EBOV) and HIV-1. This antisense tethering could also, under certain conditions, enhance a frameshifting event leading to a UGA codon in an overlapping reading frame, to allow the recoding of that UGA codon as selenocysteine. Evidence will be presented for these events being programmed in the genomes of EBOV and SARS-CoV-2. The EBOV nucleoprotein (NP) gene is an example of the reprogramming of a UGA stop codon as a potential selenocysteine codon. Using green fluorescent protein (GFP) as a downstream reporter gene, we show Se-dependent read-through of the NP 3’-UGA stop codon, which is highly conserved only in the most virulent strains of EBOV. In the EBOV polymerase (L) gene, a programmed ribosomal frameshift signal leads to an overlapping gene with two tandem UGA codons immediately followed by an RNA region that is the inverse complement (antisense) to a region of the mammalian selenoprotein, deiodinase II (DIO2) mRNA, which could both trigger the ribosomal frameshift and provide access to the SECIS element contained in the DIO2 mRNA. We have designed an innovative assay for -1 frameshifting at such sites in which upstream and downstream reporter genes are used to assess the initiation and termination of protein synthesis. By inserting wildtype or mutant viral inserts, we show a highly significant level of -1 ribosomal frameshifting at the EBOV L gene site mentioned above.  In SARS-CoV-2, we have demonstrated an antisense interaction between a region of the viral RNA and the mRNA for thioredoxin reductase 3 (TXNRD3), another selenoprotein that is highly expressed in the human testes. This predicted antisense interaction was confirmed experimentally by knockdown of TXNRD3 mRNA in SARS-CoV-2 infected Vero cells. The significance of these findings for links between Se status and the severity of COVID-19 and EBOV infection will be discussed.