Selenocysteine incorporation: A trump card in the game of mRNA decay

doi:10.1016/j.biochi.2015.01.007

Biochimie

Volume 114, July 2015, Pages 97-101

https://doi.org/10.1016/j.biochi.2015.01.007 Get rights and content

Highlights

•
The use of selenium as selenocysteine is regulated by variable mRNA stability.
•
All selenoprotein mRNAs contain premature termination codons.
•
One of the key pathways for regulation is that of nonsense mediated mRNA decay (NMD).
•
Most selenoprotein mRNAs are resistant to NMD by mechanisms that are not yet known.

Abstract

The incorporation of the 21st amino acid, selenocysteine (Sec), occurs on mRNAs that harbor in-frame stop codons because the Sec-tRNA^Sec recognizes a UGA codon. This sets up an intriguing interplay between translation elongation, translation termination and the complex machinery that marks mRNAs that contain premature termination codons for degradation, leading to nonsense mediated mRNA decay (NMD). In this review we discuss the intricate and complex relationship between this key quality control mechanism and the process of Sec incorporation in mammals.

Introduction

The utilization of the trace element selenium is primarily, if not solely, directed toward the synthesis and incorporation of the “21st” amino acid, selenocysteine (Sec). Importantly, this process requires the re-definition of a UGA codon from Stop to Sec. Fig. 1 shows a diagram of the factors required for Sec incorporation. These include the selenocysteine-specific tRNA (Sec-tRNA^Sec), the Sec-specific elongation factor (eEFSec) and an essential 3′ UTR binding protein (SBP2). While the function of an eEFSec/Sec-tRNA^Sec complex is clear, its access to the cognate UGA codons is strictly regulated by sequences in selenoprotein mRNA 3′ UTRs called Sec insertion sequences (SECIS). As a member of the kink-turn family of RNA structures, the SECIS element must interact with SBP2 in order to alter UGA codons from Stop to Sec. Ostensibly, this process is not relevant to the quality control of protein synthesis, but the fact that Sec is encoded by a stop codon means that many quality control pathways must either be avoided or regulated for efficient Sec incorporation. As such, there are two major areas that relate to translational quality control. First, eEF1A must be prevented from binding the Sec-tRNA^Sec. Second, the UGA Sec codon must not be interpreted as a premature termination codon (PTC) and induce nonsense mediated decay (NMD).

Section snippets

Elongation factor specificity

Because the Sec-tRNA^Sec harbors a cognate UCA anticodon, it is imperative that it not be bound by eEF1A and incorporated at UGA stop codons. The tRNA^Sec is unique not only because of its UCA anticodon, but in its biosynthesis as well. Newly transcribed and processed tRNA^Sec is first serylated by the Ser aminoacyl tRNA synthetase (RS), then the Ser residue is phosphorylated by a specific phosphoseryl tRNA kinase (PSTK) to generate O-phosphoserine (Sep), and finally the Sep-tRNA^Sec is converted

Interplay with nonsense mediated decay (NMD)

As mentioned above, the link between selenoprotein synthesis and translation quality control is the Sec codon, which must avoid detection as a PTC by the NMD surveillance pathway. Under conditions of adequate dietary selenium, when Sec-tRNA^Sec levels are high, NMD presumably does not occur because Sec incorporation is efficiently out-competing translation termination. This idea is somewhat challenged by the observation that several selenoprotein mRNAs were found to be incompletely loaded by

Potential mechanisms for NMD evasion

Several factors have been implicated in the differential stabilization of selenoprotein transcripts against NMD when selenium levels are inadequate. However, these factors may employ different mechanisms such as 1) influencing Sec incorporation efficiency; 2) recruiting trans factors that interfere with UPF1 or other NMD factor access and/or 3) by adopting RNA conformations that prevent stable UPF1 association or enhance UPF1 dissociation. Independently or together these factors may influence

Acknowledgments

PRC is supported by PHS grants GM077073 and GM094833.

References (41)

D. Behne et al.
Effects of a low selenium status on the distribution and retention of selenium in the rat
J. Nutr.
(1984)
D. Behne et al.
Evidence for specific selenium target tissues and new biologically important selenoproteins
Biochim. Biophys. Acta
(1988)
M.E. Budiman et al.
Eukaryotic initiation factor 4a3 is a selenium-regulated RNA-binding protein that selectively inhibits selenocysteine incorporation
Mol. Cell.
(2009)
A. Diamond et al.
Structure and properties of a bovine liver UGA suppressor serine tRNA with a tryptophan anticodon
Cell
(1981)
R.L. French et al.
Structural asymmetry of the terminal catalytic complex in selenocysteine synthesis
J. Biol. Chem.
(2014)
M. Gupta et al.
Functional analysis of the interplay between translation termination, selenocysteine codon context, and selenocysteine insertion sequence-binding protein 2
J. Biol. Chem.
(2007)
Y.S. Ho et al.
Mice deficient in cellular glutathione peroxidase develop normally and show no increased sensitivity to hyperoxia
J. Biol. Chem.
(1997)
M.T. Howard et al.
Translational redefinition of UGA codons is regulated by selenium availability
J. Biol. Chem.
(2013)
X.G. Lei et al.
Glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase are differentially regulated in rats by dietary selenium
J. Nutr.
(1995)
M.S. Saedi et al.
Effect of selenium status on mRNA levels for glutathione peroxidase in rat liver
Biochem. Biophys. Res. Commun.
(1988)

S.P. Shetty et al.

Regulation of selenocysteine incorporation into the selenium transport protein, Selenoprotein P

J. Biol. Chem.

(2014)

S.L. Weiss et al.

Selenium regulation of classical glutathione peroxidase expression requires the 3' untranslated region in Chinese hamster ovary cells

J. Nutr.

(1997)

S.L. Weiss et al.

The selenium requirement for glutathione peroxidase mRNA level is half of the selenium requirement for glutathione peroxidase activity in female rats

J. Nutr.

(1996)

J.G. Yang et al.

Dietary selenium intake controls rat plasma selenoprotein P concentration

J. Nutr.

(1989)

N. Bouzaidi-Tiali et al.

Elongation factor 1a mediates the specificity of mitochondrial tRNA import in T. brucei

EMBO J.

(2007)

J.L. Bubenik et al.

Alternative transcripts and 3'UTR elements Govern the incorporation of selenocysteine into selenoprotein S

PLoS One

(2013)

M.E. Budiman et al.

Identification of a signature motif for the eIF4a3-SECIS interaction

Nucleic Acids Res.

(2011)

A. Chester et al.

The apolipoprotein B mRNA editing complex performs a multifunctional cycle and suppresses nonsense-mediated decay

EMBO J.

(2003)

J. Donovan et al.

Selenocysteine insertion sequence binding protein 2L is implicated as a novel post-transcriptional regulator of selenoprotein expression

PLoS One

(2012)

J.E. Fletcher et al.

Polysome distribution of phospholipid hydroperoxide glutathione peroxidase mRNA: evidence for a block in elongation at the UGA/selenocysteine codon

RNA

(2000)

Cited by (30)

Stratification of lung squamous cell carcinoma based on ferroptosis regulators: Potential for new therapeutic strategies involving ferroptosis induction
2022, Lung Cancer
Citation Excerpt :
Interestingly, no correlation has been reported between the mRNA and protein levels of GPX4 [14]. Furthermore, the expression of GPX4 was found to be affected by post-translational modifications due to nonsense mediated decay [37,43]. Similar to GPX4, FSP1 is reportedly subjected to post-transcriptional regulation by miR-214 [44].
Lung squamous cell carcinoma (LSCC) exhibits poor response to treatment compared with other lung cancer subtypes, resulting in worse prognosis. Therefore, new therapeutic strategies are required for advanced LSCC. Ferroptosis is a recently discovered nonapoptotic cell death caused by intracellular lipid peroxidation that can bring about effective cell death in cancer cells resistant to apoptosis. Hence, ferroptosis is a potential therapeutic strategy for refractory cancer.
In this study, we performed clinicopathological and molecular analyses on tumor specimens from 270 patients with squamous cell lung cancer, focusing on the expression of glutathione peroxidase 4 (GPX4) and ferroptosis suppressor protein 1 (FSP1), which are known to be key regulators of ferroptosis, and the accumulation of 4-hydroxynoneral (4-HNE), a lipid peroxidation marker.
Immunohistochemistry revealed that patients with low 4-HNE accumulation and low levels of GPX4 or FSP1 had significantly worse prognoses than other patients (P = 0.001). This stratification was an independent prognostic predictor (P = 0.003). A dramatic cell death synergistic effect was observed on LSCC-derived LK-2 and EBC1 cells treated with GPX4 and FSP1 inhibitors. This effect was completely inhibited by treatment with the ferroptosis inhibitor. Notably, this was not the case in LK-2 cells treated with the apoptosis inhibitor, and in these cells, ferroptosis was induced.
Ferroptosis regulators GPX4 and FSP1 are associated with lung squamous cell cancer cancer’s prognosis. We present the clinicopathological and molecular basis of novel therapeutic strategies for refractory LSCC.
SECISBP2 is a novel prognostic predictor that regulates selenoproteins in diffuse large B-cell lymphoma
2021, Laboratory Investigation
The overexpression of glutathione peroxidase 4 (GPX4; an enzyme that suppresses peroxidation of membrane phospholipids) is considered a poor prognostic predictor of diffuse large B-cell lymphoma (DLBCL). However, the mechanisms employed in GPX4 overexpression remain unknown. GPX4 is translated as a complete protein upon the binding of SECISBP2 to the selenocysteine insertion sequence (SECIS) on the 3′UTR of GPX4 mRNA. In this study, we investigated the expression of SECISBP2 and its subsequent regulation of GPX4 and TXNRD1 in DLBCL patients. Moreover, we determined the significance of the expression of these selenoproteins in vitro using MD901 and Raji cells. SECISBP2 was positive in 45.5% (75/165 cases) of DLBCL samples. The SECISBP2-positive group was associated with low overall survival (OS) as compared to the SECISBP2-negative group (P = 0.006). Similarly, the SECISBP2 and GPX4 or TXNRD1 double-positive groups (P < 0.001), as well as the SECISBP2, GPX4, and TXNRD1 triple-positive group correlated with poor OS (P = 0.001), suggesting that SECISBP2 may serve as an independent prognostic predictor for DLBCL (hazard ratio (HR): 2.693, P = 0.008). In addition, western blotting showed a decrease in GPX4 and TXNRD1 levels in SECISBP2-knockout (KO) MD901 and Raji cells. Oxidative stress increased the accumulation of reactive oxygen species in SECISBP2-KO cells (MD901; P < 0.001, Raji; P = 0.020), and reduced cell proliferation (MD901; P = 0.001, Raji; P = 0.030), suggesting that SECISBP2-KO suppressed resistance to oxidative stress. Doxorubicin treatment increased the rate of cell death in SECISBP2-KO cells (MD901; P < 0.001, Raji; P = 0.048). Removal of oxidative stress inhibited the altered cell death rate. Taken together, our results suggest that SECISBP2 may be a novel therapeutic target in DLBCL.
SECISBP2 overexpression is an independent negative prognostic predictor in diffuse large B-cell lymphoma. Additionally, SECISBP2 positively correlates with selenoprotein expression. In vitro, SECISBP2 knockout increases intracellular reactive oxygen species accumulation via the downregulation of selenoproteins, inhibiting cell growth and promoting cell death after doxorubicin treatment. Therefore, SECISBP2 is a potential therapeutic target for malignant lymphoma.
Selenium and selenoproteins: from endothelial cytoprotection to clinical outcomes
2019, Translational Research
Citation Excerpt :
Selenoproteins incorporate selenocysteine during a sequence of post-transcription events.50,106 Selenoprotein biosynthesis may not be affected only by the availability of Se, but also by the activity of components of the selenocysteine incorporation complex, such as selenocysteine-specific tRNA, selenocysteine-specific elongation factor, and an essential 3′ UTR binding protein known as SBP2.107 Thus, a decrease in Se exposure does not affect all selenoproteins in the same way.
The role of the vascular endothelium in inflammation was demonstrated experimentally through biomarkers of endothelial dysfunction and cytoprotection. Selenium is a trace element essential for cell protection against oxidative lesions triggered by reactive oxygen species or inflammatory responses. Preclinical studies have demonstrated a relationship between adhesion molecules as biomarkers of endothelial dysfunction and selenoproteins as biomarkers of selenium status under conditions that mimic different diseases. Most studies in humans indicate an association between selenium deficiency and increased risk of morbidity and mortality, yet the pathophysiology of selenium in endothelial activation remains unknown. Here, we summarize selenium-dependent endothelial function evaluation techniques and focus on the role of selenium in endothelial cytoprotection according to current scientific knowledge. Most studies on the role of selenium in endothelial processes show selenium-dependent endothelial functions and explain how cells and tissues adapt to inflammatory insults. Taken together, these studies show an increase in adhesion molecules and a decrease in the expression of selenoproteins following a decreased exposure to selenium. Few clinical trials have enough methodological quality to be included in meta-analysis on the benefits of selenium supplementation. Furthermore, the methodology adopted in many studies does not consider the relevant findings on the pathophysiology of endothelial dysfunction. Preclinical studies should be more frequently integrated into clinical studies to provide clearer views on the role of selenium status in endothelial cytoprotection.
Identification of FAM96B as a novel selenoprotein W binding partner in the brain
2019, Biochemical and Biophysical Research Communications
Citation Excerpt :
It is also critical for brain function, and any disruption in Se homeostasis can cause neurodegeneration [3–5]. Se exerts its biological function in the form of the amino acid selenocysteine (Sec) in a unique class of proteins called selenoproteins [6]. Sec is encoded by the stop codon UGA by a mechanism known as translational recoding, which is difficult to replicate in heterologous expression systems, thereby limiting the structural and functional studies on selenoproteins.
Selenoprotien W (SelW) plays a key role in brain development, although the exact biological function and mechanisms remain unclear. We performed a yeast two-hybrid screen on a human fetal brain cDNA library and identified FAM96B as a novel binding partner of SelW. FRET analyses confirmed the interaction between SelW' and FAM96B. The mutated SelW' construct was cloned and overexpressed in E. coli, and a pull-down assay verified a direct interaction between SelW' and FAM96B. Finally, Co-Immunoprecipitation on murine brain tissue proteins demonstrated an endogenous interaction between the two proteins in the brain. Taken together, our findings prove a direct interaction between SelW and FAM96B, which may provide new insights into the role of SelW in brain development and neurodegenerative diseases.
Translation regulation of mammalian selenoproteins
2018, Biochimica et Biophysica Acta - General Subjects
Citation Excerpt :
Several selenoprotein mRNAs could fulfill criteria for NMD surveillance. However, this control key has been found to be restricted to specific selenoprotein mRNAs, including SelenoH, SelenoW and to a lesser extent Gpx1 and Gpx4 in specific tissue and conditions [112]. Additionally, another gene specific modification has been found at the 5′-end of several selenoprotein mRNAs, including MsrB1, Gpx1, Gpx4, SelenoM and SelenoW.
Interest in selenium research has considerably grown over the last decades owing to the association of selenium deficiencies with an increased risk of several human diseases, including cancers, cardiovascular disorders and infectious diseases. The discovery of a genetically encoded 21^st amino acid, selenocysteine, is a fascinating breakthrough in molecular biology as it is the first addition to the genetic code deciphered in the 1960s. Selenocysteine is a structural and functional analog of cysteine, where selenium replaces sulfur, and its presence is critical for the catalytic activity of selenoproteins.
The insertion of selenocysteine is a non-canonical translational event, based on the recoding of a UGA codon in selenoprotein mRNAs, normally used as a stop codon in other cellular mRNAs. Two RNA molecules and associated partners are crucial components of the selenocysteine insertion machinery, the Sec-tRNA^[Ser]Sec devoted to UGA codon recognition and the SECIS elements located in the 3′UTR of selenoprotein mRNAs.
The translational UGA recoding event is a limiting stage of selenoprotein expression and its efficiency is regulated by several factors.
The control of selenoproteome expression is crucial for redox homeostasis and antioxidant defense of mammalian organisms. In this review, we summarize current knowledge on the co-translational insertion of selenocysteine into selenoproteins, and its layers of regulation.
Molecular mechanism of selenoprotein P synthesis
2018, Biochimica et Biophysica Acta - General Subjects
Citation Excerpt :
The first UGA in the SELENOP gene is the only Sec codon positioned upstream of introns and can potentially invoke the nonsense mediated decay (NMD) pathway. NMD is a quality control mechanism that detects the presence of a ribosome stalling at a premature termination codon (PTC) located >50–55 nucleotides from the exon-exon junction [31]. Thus in the event that an essential component of the Sec incorporation machinery is unavailable, the naturally low efficiency of decoding at the first UGA will either be dramatically reduced or will not occur, thereby resulting in stalling ribosomes and NMD.
Selenoprotein synthesis requires the reinterpretation of a UGA stop codon as one that encodes selenocysteine (Sec), a process that requires a set of dedicated translation factors. Among the mammalian selenoproteins, Selenoprotein P (SELENOP) is unique as it contains a selenocysteine-rich domain that requires multiple Sec incorporation events.
In this review we elaborate on new data and current models that provide insight into how SELENOP is made.
SELENOP synthesis requires a specific set of factors and conditions.
As the key protein required for proper selenium distribution, SELENOP stands out as a lynchpin selenoprotein that is essential for male fertility, proper neurologic function and selenium metabolism.

View all citing articles on Scopus

View full text

Mini-reviewSelenocysteine incorporation: A trump card in the game of mRNA decay

Highlights

Abstract

Introduction

Section snippets

Elongation factor specificity

Interplay with nonsense mediated decay (NMD)

Potential mechanisms for NMD evasion

Acknowledgments

J. Nutr.

Biochim. Biophys. Acta

Mol. Cell.

Cell

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

J. Biol. Chem.

J. Nutr.

Biochem. Biophys. Res. Commun.

J. Biol. Chem.

J. Nutr.

J. Nutr.

J. Nutr.

Elongation factor 1a mediates the specificity of mitochondrial tRNA import in T. brucei

EMBO J.

Alternative transcripts and 3'UTR elements Govern the incorporation of selenocysteine into selenoprotein S

PLoS One

Identification of a signature motif for the eIF4a3-SECIS interaction

Nucleic Acids Res.

The apolipoprotein B mRNA editing complex performs a multifunctional cycle and suppresses nonsense-mediated decay

EMBO J.

Selenocysteine insertion sequence binding protein 2L is implicated as a novel post-transcriptional regulator of selenoprotein expression

PLoS One

Polysome distribution of phospholipid hydroperoxide glutathione peroxidase mRNA: evidence for a block in elongation at the UGA/selenocysteine codon

RNA

Mini-review
Selenocysteine incorporation: A trump card in the game of mRNA decay