We are trying to understand the mechanism of redox regulation of cellular processes. Our focus is on reactive oxygen species (ROS) and thiol-disulfide oxidoreductase functions of cellular components. Little is known what are specific targets of ROS and how oxidant and antioxidant signals are transmitted in the cell. To understand the mechanism of redox regulation, we need to know the identities and functions of most of the participants in the redox process. Thus, we are developing and employing various bioinformatics approaches that take advantage of genome sequencing, proteomics and functional genomics projects, and which are followed with in vitro and in vivo tests of the in silico predictions.

In mammals, two major redox systems, thioredoxin and glutathione systems, are dependent on the trace element selenium, which is an essential component of various redox enzymes. Selenium is present in proteins in the form of the 21^st amino acid, selenocysteine (Sec). Sec is co-translationally inserted in protein in response to the UGA codon with the help of the SECIS element, an mRNA stem-loop structure present in 3’-untranslated regions of selenoprotein genes. Because UGA is interpreted as a stop signal by available gene annotation tools, selenoprotein genes are typically annotated incorrectly in sequence databases, including published human genome assemblies. To overcome this problem, we are identifying selenoprotein genes by genome-wide searches for structural and thermodynamic properties of SECIS elements. We also are identifying other redox proteins by genome-wide searches for specific redox motifs present within secondary structure patterns. Subsequently, we are characterizing functions, regulation and specific targets of selenoproteins and other important redox enzymes to gain a system-wide view on redox regulation of cellular processes.

One of our current projects involves the 15 kDa selenoprotein (Sep15). We identified Sep15 as a candidate protein that mediates the cancer chemopreventive effect of selenium. We currently are characterizing its function and role in cancer prevention to identify a mechanism by which dietary selenium decreases cancer incidence.

Another project involves the functional characterization of animal thioredoxin reductases (TRs). Mammals evolved three thioredoxin reductases: cytosolic TR1, testes-enriched TR2 and mitochondrial TR3. Each of these proteins occurs in multiple forms that are generated by alternative first exon splicing. In addition, TR2 is a natural fusion of TR and glutaredoxin domains, may function as thioredoxin and glutathione reductase (TGR) and appears to be involved in male reproduction.

We recently found that Selenoprotein R (SelR), one of the selenoproteins that we initially identified through bioinformatics searches for SECIS elements, functions as methionine-R-sulfoxide reductase. Methionine sulfoxide reduction has been implicated in regulating the lifespan in animals. We would like to determine the role of SelR in aging as well as the mechanism by which methionine sulfoxide reduction regulates lifespan.

We hope that our studies will provide a better understanding of the role of redox processes in physiological and pathophysiological states, particularly in regard to cancer, aging and male reproduction, and will lead to new therapeutic and disease-preventive agents.