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Regulation of gene expression at the translational level. incorporation and utilization of selenocysteineOur primary research question targets the protein synthetic machinery as one of the primary sites for the regulation of gene expression and an important sensor of the status of cellular metabolite concentrations including trace elements. The utilization of selenium exemplifies this relationship. and is required for the synthesis and function of an essential group of proteins that contain the amino acid selenocysteine (Sec). In fact. many selenoproteins are known to provide protection from cellular damage and transformation. thus making the synthesis and regulation of these proteins an essential area of research. Sec is incorporated into these proteins by a translational recoding event at specific Stop (UGA) codons that are found upstream of stable stem-loop structures known as Sec insertion sequence (SECIS) elements. While the UGA codon and the SECIS element are the only known cis-acting elements required for Sec incorporation. at least two trans-acting factors are also required: 1) the Sec-specific elongation factor (eEFSec) and 2) a SECIS binding protein (SBP2). One of the ultimate goals for selenocysteine research is to be able to specifically regulate the expression of potentially beneficial selenoproteins in vivo. In order to achieve this goal. we must understand all of the factors that contribute not only to the basic Sec incorporation reaction but also to the regulation of this process. In addition to characterizing the structure and function of the known factors. much of our work is designed to test hypotheses regarding the identity and function of novel factors involved in the synthesis of selenoproteins utilizing both mammalian systems as well as yeast. a eukaryotic system that is devoid of the Sec incorporation machinery. The results derived from these experiments will not only significantly add to our current knowledge of Sec incorporation. but they will also provide insight into the basic mechanisms of protein synthesis during the elongation and termination phases. Within the realm of selenium biology. it has been established that increases in dietary selenium significantly reduce the incidence of prostate cancer. but the molecular basis for this effect is unknown. There are two major pathways for selenium bio-activity: 1) through the formation of selenium-containing small molecules that may promote chemopreventive apoptosis and/or 2) through the synthesis of anti-oxidative selenium-containing proteins (selenoproteins). Much of the current work on this problem focuses on the former of these possibilities. while very little effort has been directed toward understanding the role of regulated selenoprotein synthesis. Our study of the basic mechanisms required for Sec incorporation leaves us in an ideal position to carefully assess the contribution of the Sec incorporation pathway to chemoprevention using prostate cancer as a model. Toward this end. we are currently monitoring selenoprotein synthesis in normal and cancerous prostate cells as well as developing a cell-culture model for selenium chemoprevention. Selected PublicationsDonovan J, Copeland PR. (2009) Threading the needle: getting selenocysteine into proteins. Antioxid Redox Signal. Sep 11. [Epub ahead of print] Donovan J, Copeland PR. (2009) Evolutionary history of selenocysteine incorporation from the perspective of SECIS binding proteins. BMC Evol Biol. 9:229. Bockhorn J, Balar B, He D, Seitomer E, Copeland PR, Kinzy TG. (2008) Genome-wide screen of Saccharomyces cerevisiae null allele strains identifies genes involved in selenomethionine resistance. Proc Natl Acad Sci U S A. 105(46):17682-17687. Donovan J, Caban K, Ranaweera R, Gonzales-Flores JN, Copeland PR. (2008) A novel protein domain induces high affinity selenocysteine insertion sequence binding and elongation factor recruitment. J Biol Chem. 283(50):35129-39. Seitomer E, Balar B, He D, Copeland PR, Kinzy TG. (2008) Analysis of Saccharomyces cerevisiae null allele strains identifies a larger role for DNA damage versus oxidative stress pathways in growth inhibition by selenium. Mol Nutr Food Res. 52(11):1305-15. Gupta M, Copeland PR. (2007) Functional analysis of the interplay between translation termination, selenocysteine codon context, and selenocysteine insertion sequence-binding protein 2. J Biol Chem. 282(51):36797-807. Caban K, Kinzy SA, Copeland PR. (2007) The L7Ae RNA binding motif is a multifunctional domain required for the ribosome-dependent Sec incorporation activity of Sec insertion sequence binding protein 2. Mol Cell Biol. 27(18):6350-60. Rebsch CM, Penna FJ 3rd, Copeland PR. (2007) Selenoprotein expression is regulated at multiple levels in prostate cells. Cell Res. 17(3):272. Rebsch CM, Penna FJ 3rd, Copeland PR. (2006) Selenoprotein expression is regulated at multiple levels in prostate cells. Cell Res. 16(12):940-8. Caban K, Copeland PR. (2006) Size matters: a view of selenocysteine incorporation from the ribosome. Cell Mol Life Sci. 63(1):73-81. Review. Kinzy SA. Caban K. Copeland PR. (2005) Characterization of the SECIS binding protein 2 complex required for the co-translational insertion of selenocysteine in mammals. Nucleic Acids Res. 33(16):5172-80. Copeland. P.R. (2005) Making sense of nonsense: the evolution of selenocysteine usage in proteins. Genom. Biol. 6:221. Mehta. A.. Rebsch. C.M.. Kinzy. S.A.. Fletcher. J.E. and Copeland P.R. (2004) Efficiency of mammalian selenocysteine incorporation. J. Biol. Chem. 279:38852-59. Driscoll. D.M. and Copeland. P.R. (2003). Mechanism and regulation of selenoprotein synthesis. Ann Rev Nutr. 23:17-40. Copeland. P.R. (2003). Regulation of gene expression by stop codon recoding: selenocysteine. Gene. 312:17-25. |
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