Selenoprotein TRXR-1 and GSR-1 are essential for removal of old cuticle during molting in Caenorhabditis elegans

Abstract

Selenoproteins, in particular thioredoxin reductase, have been implicated in countering oxidative damage occurring during aging but the molecular functions of these proteins have not been extensively investigated in different animal models. Here we demonstrate that TRXR-1 thioredoxin reductase, the sole selenoprotein in Caenorhabditis elegans, does not protect against acute oxidative stress but functions instead together with GSR-1 glutathione reductase to promote the removal of old cuticle during molting. We show that the oxidation state of disulfide groups in the cuticle is tightly regulated during the molting cycle, and that when trxr-1 and gsr-1 function is reduced, disulfide groups in the cuticle remain oxidized. A selenocysteine-to-cysteine TRXR-1 mutant fails to rescue molting defects. Furthermore, worms lacking SELB-1, the C. elegans homolog of Escherichia coli SelB or mammalian EFsec, a translation elongation factor known to be specific for selenocysteine in E. coli, fail to incorporate selenocysteine, and display the same phenotype as those lacking trxr-1. Thus, TRXR-1 function in the reduction of old cuticle is strictly selenocysteine dependent in the nematode. Exogenously supplied reduced glutathione reduces disulfide groups in the cuticle and induces apolysis, the separation of old and new cuticle, strongly suggesting that molting involves the regulated reduction of cuticle components driven by TRXR-1 and GSR-1. Using dauer larvae, we demonstrate that aged worms have a decreased capacity to molt, and decreased expression of GSR-1. Together, our results establish a function for the selenoprotein TRXR-1 and GSR-1 in the removal of old cuticle from the surface of epidermal cells.

Two Thioredoxin Reductases, trxr-1 and trxr-2, Have Differential Physiological Roles in Caenorhabditis elegans

“…The lower pKa of a selenol and the higher nucleophilicity of a selenolate confers a type of "catalytic advantage" over Cys, when attacked position of thiol-disulfide interchange reaction. Replacement of Sec with Cys in TRXR-1 completely eliminated catalytic activity to reduce thioredoxin (Stenvall et al, 2011). Interestingly, the same Sec replacement in TRXR-1 as well as selenolate TRXR-1 successfully restored vital-dye staining defect, dependent on V-ATPase activity, which did not require thioredoxin.…”

“…development (Stenvall et al, 2011). Therefore, we asked whether the reduced V-ATPase activity in trxr-1(jh143) requires thioredoxin system by observing acridine orange uptake in the condition absent of cytoplasmic thioredoxin, TRX-1 (Jee et al, 2005).…”

Protective efficacy of selenite against lead-induced neurotoxicity in Caenorhabditis elegans

“…In contrast to other animals, TRXR-1, an ortholog of the human enzymatic antioxidant thioredoxin reductase-1, has been reported to be the only selenoprotein in C. elegans [42][43][44]. Recent study showed that trxr-1 null mutant did not show increased sensitivity to oxidative stress after incubation in 2 mM H 2 O 2 for 2 h [45]. Further investigation will be needed to determine whether Se incorporates into enzymatic antioxidant selenoprotein and the precise mechanisms by which Se(IV) regulates TRXR-1 in C elegans.…”

DNA Replication in Animal Systems Lacking Thioredoxin Reductase I

“…Thus, whereas we cannot exclude the possibility that there could be some rare cell types in mice in which replication is critically dependent on TrxR1, our efforts to date have failed to pinpoint any such cell types. Recently, a study was reported on disruption of TrxR1 in another metazoan, the nematode C. elegans (Stenvall et al, 2011). C. elegans has only a single TrxR protein, and this is the only Seccontaining protein in the worm genome (Stenvall et al, 2011).…”

“…Recently, a study was reported on disruption of TrxR1 in another metazoan, the nematode C. elegans (Stenvall et al, 2011). C. elegans has only a single TrxR protein, and this is the only Seccontaining protein in the worm genome (Stenvall et al, 2011). Surprisingly, although worms lacking TrxR1 show a molting defect due to an inability to reduce protein disulfides in the old cuticle to allow its removal, but like mouse livers lacking TrxR1 (Rollins et al, 2010;Suvorova et al, 2009), they show no evidence of oxidative stress or replicative insufficiency (Stenvall et al, 2011).…”