Abstract
The mammalian redox-active selenoprotein thioredoxin reductase (TrxR1) is a main player in redox homoeostasis. It transfers electrons from NADPH to a large variety of substrates, particularly to those containing redox-active cysteines. Previously, we reported that the classical form of cytosolic TrxR1 (TXNRD1_v1), when overexpressed in human embryonic kidney cells (HEK-293), prompted the cells to undergo differentiation [Nalvarte et al. (2004) J.Biol. Chem. 279: , 54510-54517]. In the present study,we show that several genes associated with differentiation and adhesion are differentially expressed in HEK-293 cells stably overexpressing TXNRD1_v1 compared with cells expressing its splice variant TXNRD1_v2. Overexpression of these two splice forms resulted in distinctive effects on various aspects of cellular functions including gene regulation patterns, alteration of growth rate, migration and morphology and susceptibility to selenium-induced toxicity. Furthermore, differentiation of the neuroblastoma cell line SH-SY5Y induced by all-trans retinoic acid (ATRA) increased both TXNRD1_v1 and TXNRD1_v2 expressions along with several of the identified genes associated with differentiation and adhesion. Selenium supplementation in the SH-SY5Y cells also induced a differentiated morphology and changed expression of the adhesion protein fibronectin 1 and the differentiation marker cadherin 11, as well as different temporal expression of the studied TXNRD1 variants. These data suggest that both TXNRD1_v1 and TXNRD1_v2 have distinct roles in differentiation, possibly by altering the expression of the genes associated with differentiation, and further emphasize the importance in distinguishing each unique action of different TrxR1 splice forms, especially when studying the gene silencing or knockout of TrxR1.
Highlights
The mammalian ubiquitously expressed homodimeric selenoprotein thioredoxin reductase (TrxR) belongs to the nucleotide oxido-reductase family and is a member of the thioredoxin (Trx) system [1,2,3,4,5]
We demonstrate that human embryonic kidney cell line (HEK-293) cells overexpressing either TXNRD1_v1 or its alternative splice variant TXNRD1_v2 express genes that, are involved in redox homoeostasis, and affect pathways of development, differentiation and migration, proposing an unknown, but yet important, role for TrxRs in differentiation
We show in the present study that the TxrR1 splice variants TXNRD1_v1 and TXNRD1_v2 are highly expressed and activated at an early stage of cellular differentiation, and that selenium treatment can induce differentiation phenotype in SH-SY5Y presumably through TrxR1 activation
Summary
The mammalian ubiquitously expressed homodimeric selenoprotein thioredoxin reductase (TrxR) belongs to the nucleotide oxido-reductase family and is a member of the thioredoxin (Trx) system [1,2,3,4,5]. Each homodimer of TrxRs contains a FAD and a NADPH binding motif as well as a penultimate selenocystein (Sec) residue, which makes close contact with the active site (-Cys-Val-Asn-Val-Gly-Cys-) of the adjacent subunit [6,7,8]. The incorporation of selenium in the active site relies on an intricate translation machinery, and accounts for the major ascribed physiological effects of selenium. The main substrate of TrxRs is Trx, the high reactivity of Sec at physiological pH and its accessibility at the C-terminus confer TrxRs broad substrate specificity [9]. TrxRs have been shown to reduce, and c 2015 Authors.
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