SELENOF Controls Proliferation and Cell Death in Breast-Derived Immortalized and Cancer Cells.

SELENOF expression is significantly lower in aggressive breast tumors compared to normal tissue, indicating that its reduction or loss may drive breast tumorigenesis. Deletion of SELENOF in non-tumorigenic immortalized breast epithelial MCF-10A cells resulted in enhanced proliferation, both in adherent culture and matrix-assisted three-dimmensional (3D) growth. Modulation of SELENOF in vitro through deletion or overexpression corresponded to changes in the cell-cycle regulators p21 and p27, which is consistent with breast tumor expression data from the METABRIC patient database. Together, these findings indicate that SELENOF affects both proliferation and cell death in normal epithelial and breast cancer cells, largely through the regulation of p21 and p27. In glandular cancers like breast cancer, the filling of luminal space is one of the hallmarks of early tumorigenesis. Loss of SELENOF abrogated apoptosis and autophagy, which are required for the formation of hollow acini in MCF-10A cells in matrix-assisted 3D growth, resulting in luminal filling. Conversely, overexpression of SELENOF induced cell death via apoptosis and autophagy. In conclusion, these findings are consistent with the notion that SELENOF is a breast tumor suppressor, and its loss contributes to breast cancer etiology.

SARS-CoV-2 Main Protease Targets Host Selenoproteins and Glutathione Biosynthesis for Knockdown via Proteolysis, Potentially Disrupting the Thioredoxin and Glutaredoxin Redox Cycles.

Associations between dietary selenium status and the clinical outcome of many viral infections, including SARS-CoV-2, are well established. Multiple independent studies have documented a significant inverse correlation between selenium status and the incidence and mortality of COVID-19. At the molecular level, SARS-CoV-2 infection has been shown to decrease the expression of certain selenoproteins, both in vitro and in COVID-19 patients. Using computational methods, our group previously identified a set of six host proteins that contain potential SARS-CoV-2 main protease (Mpro) cleavage sites. Here we show experimentally that Mpro can cleave four of the six predicted target sites, including those from three selenoproteins: thioredoxin reductase 1 (TXNRD1), selenoprotein F, and selenoprotein P, as well as the rate-limiting enzyme in glutathione synthesis, glutamate-cysteine ligase catalytic subunit (GCLC). Cleavage was assessed by incubating recombinant SARS-CoV-2 Mpro with synthetic peptides spanning the proposed cleavage sites, and analyzing the products via UPLC-MS. Furthermore, upon incubation of a recombinant Sec498Ser mutant of the full TXNRD1 protein with SARS-CoV-2 Mpro, the predicted cleavage was observed, destroying the TXNRD1 C-terminal redox center. Mechanistically, proteolytic knockdown of both TXNRD1 and GCLC is consistent with a viral strategy to inhibit DNA synthesis, conserving the pool of ribonucleotides for increased virion production. Viral infectivity could also be enhanced by GCLC knockdown, given the ability of glutathione to disrupt the structure of the viral spike protein via disulfide bond reduction. These findings shed new light on the importance of dietary factors like selenium and glutathione in COVID-19 prevention and treatment.

Distinct Roles of SELENOF in Different Human Cancers.

SELENOF, previously known as SEP15, is a selenoprotein that contains selenium in the form of the amino acid selenocysteine. Like other selenoproteins, the role for SELENOF in carcinogenesis has been investigated due to its altered expression compared to the corresponding normal tissue, its molecular function, and the association of genetic variations in the SELENOF gene to cancer risk or outcome. This review summarizes SELENOF's discovery, structure, cellular localization, and expression. SELENOF belongs to a new family of thioredoxin-like proteins. Published data summarized here indicate a likely role for SELENOF in redox protein quality control, and in the regulation of lipids, glucose, and energy metabolism. Current evidence indicates that loss of SELENOF contributes to the development of prostate and breast cancer, while its loss may be protective against colon cancer. Additional investigation into SELENOF's molecular mechanisms and its impact on cancer is warranted.

Role of SELENBP1 and SELENOF in prostate cancer bioenergetics.

The contribution of selenium and selenoproteins in prostate cancer etiology remains elusive, potentially due to insufficient information regarding the biochemical pathways in which they are involved. There are twenty-five human selenocysteine-containing proteins or selenoproteins as well as a smaller class of selenium-containing proteins that do not include selenocysteine, and their cancer-associated aberrations, both genetic and functional, have evoked special interest, although their contribution to the metabolic reprogramming of prostate cancers remains has not been extensively studied. While benign prostate tissue exhibits a glycolytic phenotype, neoplastic events restore the truncated tricarboxylic acid cycle and enhance oxidative phosphorylation. Two selenium-containing proteins, selenium binding protein 1 and selenoprotein F, affect prostate cancer phenotypes by modulating tumor cell metabolic profiles with significant effects on mitochondrial biology, including oxidative phosphorylation and ATP synthesis. One of the pathways affected by both proteins is the activation of adenosine monophosphate kinase and its downstream signaling with concomitant induction of glycolysis. This review focuses on highlighting the role of these two proteins in modulating the bioenergetic profile of prostate cancer and in maintaining the metabolic plasticity of these cells rendering growth advantage and possible therapeutic resistance.

Selenium and breast cancer - An update of clinical and epidemiological data.

There is an urgent need for new and improved therapeutic strategies in breast cancer, which is the most common malignancy affecting women in the United States and worldwide. Selenium (Se) is an essential trace element of the human diet and plays a critical role in many aspects of human health. Clinical and epidemiological studies summarized here clearly demonstrate that Se status correlates with breast cancer survival. As a result, one way to curb breast cancer mortality would be via Se supplementation, especially in patients with severely deplete Se status. Se manifests its biological activity through incorporation into selenoproteins as selenocysteine. However, a better understanding of tissue-specific mechanisms and roles for selenoproteins in general is required. Additionally, many human selenoproteins harbor single nucleotide polymorphisms, which impact protein expression and activity and have been associated with cancer susceptibility or impacting survival. Increasing evidence indicates that these genetic variations impinge on the interactions between Se and breast cancer. This highlights the importance of integrating the Se status with genetic factors to fully define the benefit of Se in breast cancer. While Se supplementation would clearly benefit a subset of patients, this requires first the identification of at-risk patients and warrants validation through intervention trials.

Selenoprotein F (SELENOF)-mediated AKT1-FOXO3a-PYGL axis contributes to selenium supranutrition-induced glycogenolysis and lipogenesis.

Mounting evidence showed that excess selenium (10.0-15.0-fold of adequate Se) intake caused severe hepatic lipid deposition in the vertebrate. However, the underlying mechanism remains unclear. The study was performed to elucidate the mechanism of Se supranutrition mediated-changes of lipid deposition and metabolism. We found that dietary excessive Se addition increased hepatic TGs and glucose contents, up-regulated lipogenic enzyme activities and reduced hepatic glycogen contents. Transcriptomic and immunoblotting analysis showed that Se supranutrition significantly influenced serine/threonine kinase 1 (AKT1)-forkhead box O3a (FOXO3a)-PYGL signaling and protein levels of SELENOF. Knockdown of SELENOF and PYGL by RNA interference revealed that the AKT1-FOXO3a-PYGL axis was critical for Se supranutrition-induced lipid accumulation. Moreover, Se supranutrition-induced lipid accumulation was via the increased DNA binding capacity of FOXO3a to PYGL promoter, which increased glycogenolysis, and accordingly promoted lipogenesis and lipid accumulation. Our finding provides new insight into the mechanism of Se supranutrition-induced lipid accumulation and suggests that SELENOF may be a therapeutic target for Se supranutrition induced-lipid disorders in the vertebrates.

Selenium and the 15kDa Selenoprotein Impact Colorectal Tumorigenesis by Modulating Intestinal Barrier Integrity.

Selenoproteins play important roles in many cellular functions and biochemical pathways in mammals. Our previous study showed that the deficiency of the 15 kDa selenoprotein (Selenof) significantly reduced the formation of aberrant crypt foci (ACF) in a mouse model of azoxymethane (AOM)-induced colon carcinogenesis. The objective of this study was to examine the effects of Selenof on inflammatory tumorigenesis, and whether dietary selenium modified these effects. For 20 weeks post-weaning, Selenof-knockout (KO) mice and littermate controls were fed diets that were either deficient, adequate or high in sodium selenite. Colon tumors were induced with AOM and dextran sulfate sodium. Surprisingly, KO mice had drastically fewer ACF but developed a similar number of tumors as their littermate controls. Expression of genes important in inflammatory colorectal cancer and those relevant to epithelial barrier function was assessed, in addition to structural differences via tissue histology. Our findings point to Selenof's potential role in intestinal barrier integrity and structural changes in glandular and mucin-producing goblet cells in the mucosa and submucosa, which may determine the type of tumor developing.

Dietary Selenium Supplementation Ameliorates Female Reproductive Efficiency in Aging Mice.

Female reproductive (ovarian) aging is distinctively characterized by a markedly reduced reproductive function due to a remarkable decline in quality and quantity of follicles and oocytes. Selenium (Se) has been implicated in playing many important biological roles in male fertility and reproduction; however, its potential roles in female reproduction, particularly in aging subjects, remain poorly elucidated. Therefore, in the current study we used a murine model of female reproductive aging and elucidated how different Se-levels might affect the reproductive efficiency in aging females. Our results showed that at the end of an 8-week dietary trial, whole-blood Se concentration and blood total antioxidant capacity (TAOC) were significantly reduced in Se-deficient (0.08 mg Se/kg; Se-D) mice, whereas both of these biomarkers were significantly higher in inorganic (0.33 mg/kg; ISe-S) and organic (0.33 mg/kg; OSe-S) Se-supplemented groups. Similarly, compared to the Se-D group, Se supplementation significantly ameliorated the maintenance of follicles and reduced the rate of apoptosis in ovaries. Meanwhile, the rate of in vitro-produced embryos resulting from germinal vesicle (GV) oocytes was also significantly improved in Se-supplemented (ISe-S and OSe-S) groups compared to the Se-D mice, in which none of the embryos developed to the hatched blastocyst stage. RT-qPCR results revealed that mRNA expression of Gpx1, Gpx3, Gpx4, Selenof, p21, and Bcl-2 genes in ovaries of aging mice was differentially modulated by dietary Se levels. A considerably higher mRNA expression of Gpx1, Gpx3, Gpx4, and Selenof was observed in Se-supplemented groups compared to the Se-D group. Similarly, mRNA expression of Bcl-2 and p21 was significantly lower in Se-supplemented groups. Immunohistochemical assay also revealed a significantly higher expression of GPX4 in Se-supplemented mice. Our results reasonably indicate that Se deficiency (or marginal levels) can negatively impact the fertility and reproduction in females, particularly those of an advancing age, and that the Se supplementation (inorganic and organic) can substantiate ovarian function and overall reproductive efficiency in aging females.

Role of Selenof as a Gatekeeper of Secreted Disulfide-Rich Glycoproteins.

Selenof (15-kDa selenoprotein; Sep15) is an endoplasmic reticulum (ER)-resident thioredoxin-like oxidoreductase that occurs in a complex with UDP-glucose:glycoprotein glucosyltransferase. We found that Selenof deficiency in mice leads to elevated levels of non-functional circulating plasma immunoglobulins and increased secretion of IgM during in vitro splenic B cell differentiation. However, Selenof knockout animals show neither enhanced bacterial killing capacity nor antigen-induced systemic IgM activity, suggesting that excess immunoglobulins are not functional. In addition, ER-to-Golgi transport of a target glycoprotein was delayed in Selenof knockout embryonic fibroblasts, and proteomic analyses revealed that Selenof deficiency is primarily associated with antigen presentation and ER-to-Golgi transport. Together, the data suggest that Selenof functions as a gatekeeper of immunoglobulins and, likely, other client proteins that exit the ER, thereby supporting redox quality control of these proteins.

The interaction of selenoprotein F (SELENOF) with retinol dehydrogenase 11 (RDH11) implied a role of SELENOF in vitamin A metabolism.

BACKGROUND: Selenoprotein F (SELENOF, was named as 15-kDa selenoprotein) has been reported to play important roles in oxidative stress, endoplasmic reticulum (ER) stress and carcinogenesis. However, the biological function of SELENOF is still unclear. METHODS: A yeast two-hybrid system was used to screen the interactive protein of SELENOF in a human fetal brain cDNA library. The interaction between SELENOF and interactive protein was validated by fluorescence resonance energy transfer (FRET), co-immunoprecipitation (co-IP) and pull-down assays. The production of retinol was detected by high performance liquid chromatograph (HPLC). RESULTS: Retinol dehydrogenase 11 (RDH11) was found to interact with SELENOF. RDH11 is an enzyme for the reduction of all-trans-retinaldehyde to all-trans-retinol (vitamin A). The production of retinol was decreased by SELENOF overexpression, resulting in more retinaldehyde. CONCLUSIONS: SELENOF interacts with RDH11 and blocks its enzyme activity to reduce all-trans-retinaldehyde.

Correlations of SELENOF and SELENOP genotypes with serum selenium levels and prostate cancer.

BACKGROUND: Selenium status is inversely associated with the incidence of prostate cancer. However, supplementation trials have not indicated a benefit of selenium supplementation in reducing cancer risk. Polymorphisms in the gene encoding selenoprotein 15 (SELENOF) are associated with cancer incidence/mortality and present disproportionately in African Americans. Relationships among the genotype of selenoproteins implicated in increased cancer risk, selenium status, and race with prostate cancer were investigated. METHODS: Tissue microarrays were used to assess SELENOF levels and cellular location in prostatic tissue. Sera and DNA from participants of the Chicago-based Adiposity Study Cohort were used to quantify selenium levels and genotype frequencies of the genes for SELENOF and the selenium-carrier protein selenoprotein P (SELENOP). Logistic regression models for dichotomous patient outcomes and regression models for continuous outcome were employed to identify both clinical, genetic, and biochemical characteristics that are associated with these outcomes. RESULTS: SELENOF is dramatically reduced in prostate cancer and lower in tumors derived from African American men as compared to tumors obtained from Caucasians. Differing frequency of SELENOF polymorphisms and lower selenium levels were observed in African Americans as compared to Caucasians. SELENOF genotypes were associated with higher histological tumor grade. A polymorphism in SELENOP was associated with recurrence and higher serum PSA. CONCLUSIONS: These results indicate an interaction between selenium status and selenoprotein genotypes that may contribute to the disparity in prostate cancer incidence and outcome experienced by African Americans.

Detection of Selenoproteins by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP MS) in Immobilized pH Gradient (IPG) Strips.

In contrast to other trace elements that are cofactors of enzymes and removed from proteins under denaturing conditions, Se is covalently bound to proteins when incorporated into selenoproteins, since it is a component of selenocysteine aminoacid. It implies that selenoproteins can undergo several biochemical separation methods in stringent and chaotropic conditions and still maintain the presence of selenium in the primary sequence. This feature has been used to develop a method for the detection of trace levels of human selenoproteins in cell extracts without the use of radioactive isotopes. The selenoproteins are separated as a function of their isoelectric point (pI) using iso-electrofocusing (IEF) electrophoretic strips and detected by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP MS). This method, therefore referred to as IEF-LA-ICP MS, allowed the detection of several selenoproteins in human cell lines, including Gpx1, Gpx4, TXNRD1, TXNRD2, and SELENOF.