Abstract
The human thioredoxin system has a wide range of functions in cells including regulation of cell proliferation and differentiation, immune system modulation, antioxidant defense, redox control of transcription factor activity, and promotion of cancer development. A key component of this enzymatic system is the selenoprotein thioredoxin reductase 1 (TrxR1), encoded by the TXNRD1 gene. Transcription of TXNRD1 involves alternative splicing, leading to a number of transcripts also encoding isoforms of TrxR1 that differ from each other at their N-terminal domains. Here we have studied the TXNRD1_v3 isoform containing an atypical N-terminal glutaredoxin (Grx) domain. Expression of the transcript of this isoform was found predominantly in testis but was also detected in ovary, spleen, heart, liver, kidney, and pancreas. By immunohistochemical analysis in human testis with antibodies specific for the Grx domain of TXNRD1_v3, the protein was found to be predominantly expressed in the Leydig cells. Expression of the TXNRD1_v3 transcript was also found in several cancer cell lines (HCC1937, H23, A549, U1810, or H157), and in HeLa cells, it was induced by estradiol or testosterone treatments. Surprisingly, green fluorescent protein fusions with the complete TXNRD1_v3 protein or with only its Grx domain localized to distinct cellular sites in proximity to actin, and furthermore, had a potent capacity to rapidly induce cell membrane protrusions. Analyses of these structures suggested that the Grx domain of TXNRD1_v3 localizes first in the emerging protrusion and is then followed into the protrusions by actin and subsequently by tubulin. The results presented thus reveal that TXNRD1_v3 has a unique and distinct expression pattern in human cells and suggest that the protein can guide actin polymerization in relation to cell membrane restructuring.
Highlights
Results presented reveal that TXNRD1_v3 has a unique and distinct expression pattern in human cells and suggest that the protein can guide actin polymerization in relation to cell membrane restructuring
6 The abbreviations used are: Trx, thioredoxin; thioredoxin reductases (TrxR), thioredoxin reductase; TrxR1, thioredoxin reductase 1; TrxR2, human mitochondrial TrxR isoenzyme encoded by the TXNRD2 gene; TXNRD1_v3, splice variant of human TrxR1 encoded by the 1 transcript of the TXNRD1 gene; Grx, glutaredoxin; ␣-v3, peptide antibodies raised against part of the Grx domain of v3; GFP, green fluorescent protein; TGR, human thioredoxin glutathione reductase encoded by the TXNRD3 gene; v3-GFP, fusion construct of v3 fused at its C-terminal end to GFP; v3(Grx)-GFP, fusion construct of the Grx domain of v3 fused at its C-terminal end to GFP; v3, short form notation for the human TrxR1 splice variant protein TXNRD1_v3; TBS, Tris-buffered saline; PBS, phosphate-buffered saline; DAPI, 4Ј,6-diamidino-2-phenylindole; ER, estrogen receptor
We found that the third splice variant of human TrxR1, v3, exhibits a prominent expression in Leydig cells of the testis and is expressed in a few additional tissues including ovary and several cancer cell lines
Summary
Thioredoxin; TrxR, thioredoxin reductase; TrxR1, thioredoxin reductase 1; TrxR2, human mitochondrial TrxR isoenzyme encoded by the TXNRD2 gene; TXNRD1_v3, splice variant of human TrxR1 encoded by the 1 transcript of the TXNRD1 gene; Grx, glutaredoxin; ␣-v3, peptide antibodies raised against part of the Grx domain of v3; GFP, green fluorescent protein; TGR, human thioredoxin glutathione reductase encoded by the TXNRD3 gene; v3-GFP, fusion construct of v3 fused at its C-terminal end to GFP; v3(Grx)-GFP, fusion construct of the Grx domain of v3 fused at its C-terminal end to GFP; v3, short form notation for the human TrxR1 splice variant protein TXNRD1_v3; TBS, Tris-buffered saline; PBS, phosphate-buffered saline; DAPI, 4Ј,6-diamidino-2-phenylindole; ER, estrogen receptor No information exists about the possible function(s) of v3 in human cells, which has been the focus of the present study
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