Evidence for Direct Roles of Two Additional Factors, SECp43 and Soluble Liver Antigen, in the Selenoprotein Synthesis Machinery

Authors

Xue-Ming Xu, NCI, National Institutes of Health, Bethesda, Maryland Follow
Heiko Mix, University of Nebraska-Lincoln
Bradley A. Carlson, NCI, National Institutes of Health, Bethesda, Maryland Follow
Paula J. Grabowski, University of Pittsburgh, Pittsburgh, Pennsylvania
Vadim N. Gladyshev, University of Nebraska-LincolnFollow
Marla J. Berry, University of Hawaii at Manoa, Honolulu, Hawaii
Dolph L. Hatfield, NCI, National Institutes of Health, Bethesda, MarylandFollow

Date of this Version

December 2005

Comments

Published in THE JOURNAL OF BIOLOGICAL CHEMISTRY, VOL. 280, NO. 50, pp. 41568–41575, December 16, 2005.

Abstract

Selenocysteine (Sec) is inserted into selenoproteins co-translationally with the help of various cis- and trans-acting factors. The specific mechanisms of Sec biosynthesis and insertion into protein in eukaryotic cells, however, are not known. Two proteins, SECp43 and the soluble liver antigen (SLA), were previously reported to interact with tRNA ^[Ser]Sec, but their functions remained elusive. Herein, we report that knockdown of SECp43 in NIH3T3 or TCMK-1 cells using RNA interference technology resulted in a reduction in the level of methylation at the 2’-hydroxylribosyl moiety in the wobble position (Um34) of Sec tRNA ^[Ser]Sec, and consequently reduced glutathione peroxidase 1 expression. Double knockdown of SECp43 and SLA resulted in decreased selenoprotein expression. SECp43 formed a complex with Sec tRNA ^[Ser]Sec and SLA, and the targeted removal of one of these proteins affected the binding of the other to Sec tRNA ^[Ser]Sec. SECp43 was located primarily in the nucleus, whereas SLA was found in the cytoplasm. Co-transfection of both proteins resulted in the nuclear translocation of SLA suggesting that SECp43 may also promote shuttling of SLA and Sec tRNA ^[Ser]Sec between different cellular compartments. Taken together, these data establish the role of SECp43 and SLA in selenoprotein biosynthesis through interaction with tRNA ^[Ser]Sec in a multiprotein complex. The data also reveal a role of SECp43 in regulation of selenoprotein expression by affecting the synthesis of Um34 on tRNA[ ^[Ser]Sec and the intracellular location of SLA.