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

Selenium as a Modulator of Redox Reactions in the Prevention and Treatment of Cardiovascular Diseases

Cardiovascular diseases stand as the predominant global cause of mortality, exerting a profound impact on both life expectancy and its quality. Given their immense public health burden, extensive efforts have been dedicated to comprehending the underlying mechanisms and developing strategies for prevention and treatment. Selenium, a crucial participant in redox reactions, emerges as a notable factor in maintaining myocardial cell homeostasis and influencing the progression of cardiovascular disorders. Some disorders, such as Keshan disease, are directly linked with its environmental deficiency. Nevertheless, the precise extent of its impact on the cardiovascular system remains unclear, marked by contradictory findings in the existing literature. High selenium levels have been associated with an increased risk of developing hypertension, while lower concentrations have been linked to heart failure and atrial fibrillation. Although some trials have shown its potential effectiveness in specific groups of patients, large cohort supplementation attempts have generally yielded unsatisfactory outcomes. Consequently, there persists a significant need for further research aimed at delineating specific patient cohorts and groups of diseases that would benefit from selenium supplementation.

Current Understanding of Human Polymorphism in Selenoprotein Genes: A Review of Its Significance as a Risk Biomarker

Selenium has been proven to influence several biological functions, showing to be an essential micronutrient. The functional studies demonstrated the benefits of a balanced selenium diet and how its deficiency is associated with diverse diseases, especially cancer and viral diseases. Selenium is an antioxidant, protecting the cells from damage, enhancing the immune system response, preventing cardiovascular diseases, and decreasing inflammation. Selenium can be found in its inorganic and organic forms, and its main form in the cells is the selenocysteine incorporated into selenoproteins. Twenty-five selenoproteins are currently known in the human genome: glutathione peroxidases, iodothyronine deiodinases, thioredoxin reductases, selenophosphate synthetase, and other selenoproteins. These proteins lead to the transport of selenium in the tissues, protect against oxidative damage, contribute to the stress of the endoplasmic reticulum, and control inflammation. Due to these functions, there has been growing interest in the influence of polymorphisms in selenoproteins in the last two decades. Selenoproteins' gene polymorphisms may influence protein structure and selenium concentration in plasma and its absorption and even impact the development and progression of certain diseases. This review aims to elucidate the role of selenoproteins and understand how their gene polymorphisms can influence the balance of physiological conditions. In this polymorphism review, we focused on the PubMed database, with only articles published in English between 2003 and 2023. The keywords used were "selenoprotein" and "polymorphism". Articles that did not approach the theme subject were excluded. Selenium and selenoproteins still have a long way to go in molecular studies, and several works demonstrated the importance of their polymorphisms as a risk biomarker for some diseases, especially cardiovascular and thyroid diseases, diabetes, and cancer.

Regulation of SELENOF translation by eIF4a3: Possible role in prostate cancer progression

The levels of the SELENOF selenoprotein are dramatically reduced in prostate cancer compared to adjacent benign tissue and reducing SELENOF in prostate epithelial cells results in the acquisition of features of the transformed phenotype. It was hypothesized that the aberrant increase in the eiF4a3 translation factor, which has an established role in RNA splicing and the regulation of selenoprotein translation, contributes to the lower levels of SELENOF. Using the available databases, eIF4a3 messenger RNA (mRNA) levels are elevated in prostate cancer compared to normal tissue as is the hypomethylation of the corresponding gene. Using a prostate cancer tissue microarray, we established that eiF4a3 levels are higher in prostate cancer tissue. Ectopic expression of eIF4a3 in prostate cancer cells reduced SELENOF levels and attenuated the readthrough of the UGA codon using a specialized reporter construct designed to examine UGA decoding, with the opposite effects observed using eIF4a3 knock-down constructs. Direct binding of eIF4a3 to the regulatory regions of SELENOF mRNA was established with pull-down experiments. Lastly, we show that an eIF4a3 inhibitor, eIF4a3-IN-2, increases SELENOF levels, UGA readthrough, and reduces binding of eIF4a3 to the SELENOF mRNA 3'-UTR in exposed cells. These data establish eIF4a3 as a likely prostate cancer oncogene and a regulator of SELENOF translation.

Selenium and Selenoproteins in Health

Selenium is a trace mineral that is essential for health. After being obtained from food and taken up by the liver, selenium performs various physiological functions in the body in the form of selenoproteins, which are best known for their redox activity and anti-inflammatory properties. Selenium stimulates the activation of immune cells and is important for the activation of the immune system. Selenium is also essential for the maintenance of brain function. Selenium supplements can regulate lipid metabolism, cell apoptosis, and autophagy, and have displayed significant alleviating effects in most cardiovascular diseases. However, the effect of increased selenium intake on the risk of cancer remains unclear. Elevated serum selenium levels are associated with an increased risk of type 2 diabetes, and this relationship is complex and nonlinear. Selenium supplementation seems beneficial to some extent; however, existing studies have not fully explained the influence of selenium on various diseases. Further, more intervention trials are needed to verify the beneficial or harmful effects of selenium supplementation in various diseases.

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.

The Associations of Selenoprotein Genetic Variants with the Risks of Colorectal Adenoma and Colorectal Cancer: Case–Control Studies in Irish and Czech Populations

Background: Selenium manifests its biological effects through its incorporation into selenoproteins, which play several roles in countering oxidative and inflammatory responses implicated in colorectal carcinogenesis. Selenoprotein genetic variants may contribute to colorectal cancer (CRC) development, as we previously observed for SNP variants in a large European prospective study and a Czech case–control cohort. Methods: We tested if significantly associated selenoprotein gene SNPs from these studies were also associated with CRC risk in case–control studies from Ireland (colorectal neoplasia, i.e., cancer and adenoma cases: 450, controls: 461) and the Czech Republic (CRC cases: 718, controls: 646). Genotyping of 23 SNPs (20 in the Irish and 13 in the Czechs) was performed by competitive specific allele-specific PCR (KASPar). Multivariable adjusted logistic regression was used to assess the associations with CRC development. Results: We found significant associations with an increased CRC risk for rs5859 (SELENOF) and rs2972994 (SELENOP) in the Irish cohort but only with rs4802034 (SELENOV) in the Czechs. Significant associations were observed for rs5859 (SELENOF), rs4659382 (SELENON), rs2972994 (SELENOP), rs34713741 (SELENOS), and the related Se metabolism gene variant rs2275129 (SEPHS1) with advanced colorectal neoplasia development. However, none of these findings retained significance after multiple testing corrections. Conclusions: Several SNPs previously associated with CRC risk were also associated with CRC or colorectal neoplasia development in either the Irish or Czech cohorts. Selenoprotein gene variation may modify CRC risk across diverse European populations, although the specific variants may differ.

Recent advances in the application of metallomics in diagnosis and prognosis of human cancer

Metals play a critical role in human health and diseases. In recent years, metallomics has been introduced and extensively applied to investigate the distribution, regulation, function, and crosstalk of metal(loid) ions in various physiological and pathological processes. Based on high-throughput multielemental analytical techniques and bioinformatics methods, it is possible to elucidate the correlation between the metabolism and homeostasis of diverse metals and complex diseases, in particular for cancer. This review aims to provide an overview of recent progress made in the application of metallomics in cancer research. We mainly focuses on the studies about metallomic profiling of different human biological samples for several major types of cancer, which reveal distinct and dynamic patterns of metal ion contents and the potential benefits of using such information in the detection and prognosis of these malignancies. Elevated levels of copper appear to be a significant risk factor for various cancers, and each type of cancer has a unique distribution of metals in biofluids, hair/nails, and tumor-affected tissues. Furthermore, associations between genetic variations in representative metalloprotein genes and cancer susceptibility have also been demonstrated. Overall, metallomics not only offers a better understanding of the relationship between metal dyshomeostasis and the development of cancer but also facilitates the discovery of new diagnostic and prognostic markers for cancer translational medicine.

SELENOF is a new tumor suppressor in breast cancer

Epidemiological evidence has indicated an inverse association between selenium status and various types of cancer, including breast cancer. Selenoproteins are the primary mediators of selenium effects in human health. We have previously reported loss of heterozygosity in breast tumor samples of the gene for one of the selenoproteins, SELENOF. The function of SELENOF remains unclear and whether SELENOF levels impact breast cancer risk or outcome is unknown. The mining of breast cancer patient databases revealed that SELENOF mRNA is significantly lower in late-stage tumor samples and lower levels of SELENOF also predict poor patient outcome from breast cancer. Genetically manipulating SELENOF in human breast cancer cells or in the murine mammary gland by overexpression, silencing or knockout impacted cell viability by affecting both proliferation and cell death. Restoring SELENOF can attenuate a number of aggressive cancer phenotypes in breast cancer cells, including clonogenic survival, and enhance the response to drugs or radiation used in breast cancer therapy. Importantly, enhancing SELENOF expression reduced in vivo tumor growth in a murine xenograft model of breast cancer. These data indicate that SELENOF is a new tumor suppressor in breast cancer.

Loss of SELENOF Induces the Transformed Phenotype in Human Immortalized Prostate Epithelial Cells

SELENOF is a member of the class of selenoproteins in which the amino acid selenocysteine is co-translationally inserted into the elongating peptide in response to an in-frame UGA codon located in the 3′-untranslated (3′-UTR) region of the SELENOF mRNA. Polymorphisms in the 3′-UTR are associated with an increased risk of dying from prostate cancer and these variations are functional and 10 times more frequent in the genomes of African American men. SELENOF is dramatically reduced in prostate cancer compared to benign adjacent regions. Using a prostate cancer tissue microarray, it was previously established that the reduction of SELENOF in the cancers from African American men was significantly greater than in cancers from Caucasian men. When SELENOF levels in human prostate immortalized epithelial cells were reduced with an shRNA construct, those cells acquired the ability to grow in soft agar, increased the ability to migrate in a scratch assay and acquired features of energy metabolism associated with prostate cancer. These results support a role of SELENOF loss in prostate cancer progression and further indicate that SELENOF loss and genotype may contribute to the disparity in prostate cancer mortality experienced by African American men.

The influence of nutrigenetics on biomarkers of selenium nutritional status

Selenium (Se) is an essential micronutrient for human biology that executes its functions as the amino acid selenocysteine via selenoproteins, which have important functions in, for example, antioxidation, immunomodulation, thyroid metabolism, and human fertility. Se nutritional status is assessed using the quantification of blood Se biomarkers, which are influenced by several factors, including diet, age, gender, smoking status, alcohol consumption, health condition, and the genetic characteristics of individuals. Nutrigenetic studies have identified single nucleotide polymorphisms in selenoproteins that might clarify the high variability in values reported for biomarkers of Se nutritional status in different populations, and the response of these biomarkers to Se supplementation with either organic or inorganic forms of Se. This review aims to (1) define the basic aspects of Se biology, (2) describe the current most commonly used biomarkers of Se nutritional status, and (3) provide a summary of associations between functional single nucleotide polymorphisms in selenoproteins and biomarkers of Se status in healthy populations.

Integrated Analysis to Study the Relationship between Tumor-Associated Selenoproteins: Focus on Prostate Cancer

Selenoproteins are proteins that contain selenium within selenocysteine residues. To date, twenty-five mammalian selenoproteins have been identified; however, the functions of nearly half of these selenoproteins are unknown. Although alterations in selenoprotein expression and function have been suggested to play a role in cancer development and progression, few detailed studies have been carried out in this field. Network analyses and data mining of publicly available datasets on gene expression levels in different cancers, and the correlations with patient outcome, represent important tools to study the correlation between selenoproteins and other proteins present in the human interactome, and to determine whether altered selenoprotein expression is cancer type-specific, and/or correlated with cancer patient prognosis. Therefore, in the present study, we used bioinformatics approaches to (i) build up the network of interactions between twenty-five selenoproteins and identify the most inter-correlated proteins/genes, which are named HUB nodes; and (ii) analyze the correlation between selenoprotein gene expression and patient outcome in ten solid tumors. Then, considering the need to confirm by experimental approaches the correlations suggested by the bioinformatics analyses, we decided to evaluate the gene expression levels of the twenty-five selenoproteins and six HUB nodes in androgen receptor-positive (22RV1 and LNCaP) and androgen receptor-negative (DU145 and PC3) cell lines, compared to human nontransformed, and differentiated, prostate epithelial cells (EPN) by RT-qPCR analysis. This analysis confirmed that the combined evaluation of some selenoproteins and HUB nodes could have prognostic value and may improve patient outcome predictions.

The Interaction between Dietary Selenium Intake and Genetics in Determining Cancer Risk and Outcome

There is considerable interest in the trace element selenium as a possible cancer chemopreventive dietary component, but supplementation trials have not indicated a clear benefit. Selenium is a critical component of selenium-containing proteins, or selenoproteins. Members of this protein family contain selenium in the form of selenocysteine. Selenocysteine is encoded by an in-frame UGA codon recognized as a selenocysteine codon by a regulatory element, the selenocysteine insertion sequence (SECIS), in the 3′-untranslated region of selenoprotein mRNAs. Epidemiological studies have implicated several selenoprotein genes in cancer risk or outcome based on associations between allelic variations and disease risk or mortality. These polymorphisms can be found in or near the SECIS or in the selenoprotein coding sequence. These variations both function to control protein synthesis and impact the efficiency of protein synthesis in response to the levels of available selenium. Thus, an individual’s genetic makeup and nutritional intake of selenium may interact to predispose them to acquiring cancer or affect cancer progression to lethality.

Absolute quantification of selenoproteins and selenometabolites in lung cancer human serum by column switching coupled to triple quadrupole inductively coupled plasma mass spectrometry

One of the most important causes of the high mortality rate and low life expectancy of lung cancer is the detection at advanced stages. Thus, there is an urgent need for early diagnosis and the search of new selective biomarkers. Selenium is an important constituent of selenoproteins and a powerful antioxidant able to protect against cancer. In this work, the absolute quantification of selenium in selenoproteins and the total content in selenometabolites has been performed for the first time in serum from lung cancer patients (LC) and healthy controls (HC). To this end, a method for the simultaneous speciation of selenoproteins using size exclusion chromatography (SEC) and affinity chromatography (AF) with detection by ICP-QQQ-MS, and quantification by isotopic dilution (IDA) (SEC-AF-HPLC-SUID-ICP-QQQ-MS) was developed to determine the selenium concentration in eGPx, SEPP1 and SeAlb, as well as total selenometabolites, to find alterations that may serve as biomarkers of this disease. In the same way, a method based on anion-exchange chromatography coupled to ICP-QQQ-MS was developed to quantify selenometabolites (SeCys2, SeMeSeCys, SeMet, selenite and selenate) in the same LC and HC serum samples. The results showed that the averaged concentrations of selenium in eGPx, SeAlb and selenite were significantly higher in LC patients (LC (eGPx: 21.24 ± 0.77 ng g^-1; SeAlb: 49.56 ± 3.16 ng g^-1 and Se(IV): 6.20 ± 1.22 ng g^-1) than in HC group (eGPx: 16.96 ± 0.53 ng g^-1; SeAlb: 38.33 ± 2.66 ng g^-1 and Se(IV): 3.56 ± 0.55 ng g^-1). In addition, the ratios between selenoproteins and selenometabolites have been calculated for the first to study their potential use as LC biomarkers. The rates eGPx/SEPP1, SEPP1/SeAlb, eGPx/Se(IV) and SEPP1/Se(IV) were significantly different between LC and HC groups.

Selenium Supplementation and Prostate Health in a New Zealand Cohort

Background: There is variable reporting on the benefits of a 200 μg/d selenium supplementation towards reducing prostate cancer impacts. The current analysis is to understand whether stratified groups receive supplementation benefits on prostate health. Methods: 572 men were supplemented with 200 µg/d selenium as selinized yeast for six months, and 481 completed the protocol. Selenium and prostate-specific antigen (PSA) levels were measured in serum at pre- and post-supplementation. Changes in selenium and PSA levels subsequent to supplementation were assessed with and without demographic, lifestyle, genetic and dietary stratifications. Results: The post-supplementation selenium (p = 0.002) and the gain in selenium (p < 0.0001) by supplementation were significantly dependent on the baseline selenium level. Overall, there was no significant correlation between changes in PSA and changes in selenium levels by supplementation. However, stratified analyses showed a significant inverse correlation between changes in PSA and changes in selenium in men below the median age (p = 0.048), never-smokers (p = 0.031), men carrying the GPX1 rs1050450 T allele (CT, p = 0.022 and TT, p = 0.011), dietary intakes above the recommended daily intake (RDI) for zinc (p < 0.05), and below the RDI for vitamin B12 (p < 0.001). Conclusions: The current analysis shows the influence of life factors on prostate health benefits of supplemental selenium.

Selenoproteins of the Human Prostate: Unusual Properties and Role in Cancer Etiology

The prostate is an important organ for the maintenance of sperm health with prostate cancer being a common disease for which there is a critical need to distinguish indolent from aggressive disease. Several selenium-containing proteins have been implicated in prostate cancer risk or outcome due to either enzyme function, the reduced levels of these proteins being associated with cancer recurrence after prostatectomy or their corresponding genes containing single-nucleotide polymorphisms associated with increased risk. Moreover, experimental data obtained from the manipulation of either cultured cells or animal models have indicated that some of these proteins are contributing mechanistically to prostate cancer incidence or progression. Among these are selenocysteine-containing proteins selenoprotein P (SELENOP), glutathione peroxidase (GPX1), and selenoprotein 15 (SELENOF); and the selenium-associated protein selenium-binding protein 1 (SBP1). Genotyping of some of the genes for these proteins has identified functional single-nucleotide polymorphisms that are associated with prostate cancer risk and the direct quantification of these proteins in human prostate tissues has not only revealed associations to clinical outcomes but have also identified unique properties that are different from what is observed in other tissue types. The location of GPX1 in the nucleus and SELENOF in the plasma membrane of prostate epithelial cells indicates that these proteins may have functions in normal prostate tissue that are distinct from that of the other tissue types.

Interaction of NKX3.1 and SELENOP genotype with prostate cancer recurrence

BACKGROUND

NKX3.1 is a tumor suppressor frequently lost in prostate cancer. Previous studies by others indicated that the risks associated with reduced NKX3.1 levels can be enhanced by anti-oxidant supplementation. Selenium is an essential component of several proteins with anti-oxidant functions and lower levels of selenium have been associated with greater risk of prostate cancer. In contrast, participants of the select prostate cancer prevention trial were at increased risk of prostate cancer when supplemented with selenium when their baseline selenium levels were high.

METHODS

In order to investigate whether there was an interaction between a functional polymorphism in NKX3.1 that results in less protein and selenium status with prostate cancer grade or outcome, plasma selenium levels and the genotypes of NKX3.1 and the selenium carrier protein SELENOP were determined from a cohort of men who underwent radical protatectomy.

RESULTS

NKX3.1 and SELENOP genotypes were associated with a more aggressive prostate tumor grade at the time of prostatectomy, but there were no significant interactions of NKX3.1 genotype with either selenium status or SELENOP genotype. There was also a significant association between NKX3.1 genotype and prostate cancer recurrence, however this association was modified by SELENOP genotype, but not with plasma selenium levels.

CONCLUSIONS

These data indicate that the impact of selenium status on prostate cancer may be influenced by factors other than the amount of selenium in circulation.

GPX1 Localizes to the Nucleus in Prostate Epithelium and its Levels are not Associated with Prostate Cancer Recurrence

Glutathione peroxidase 1 (GPX1) is an extensively studied selenium-dependent protein that reduces hydrogen and lipid peroxides to water. Because of its antioxidant function and its responsiveness to dietary intakes of selenium, an essential trace element whose levels are inversely associated with prostate cancer risk, GPX1 levels were assessed in a prostate cancer tissue microarray, comparing cases of recurrent prostate cancer following prostatectomy to non-recurrent controls. While GPX1 is generally considered as a protein that resides in both the cytoplasm and mitochondria, we detected strong nuclear staining by immunofluorescence using GPX1-specific antibodies. Nuclear localization of GPX1 was also observed in both primary prostate epithelial cells and the immortalized prostate-derived cell line RWPE-1, but not in LNCaP or PC3 prostate tumor-derived cell lines. Quantification of GPX1 levels in the entire cell, the cytoplasm, and the nucleus did not indicate any association of either its levels or subcellular distribution with prostate cancer recurrence. While GPX1 levels may not have an impact on survival among men with prostate cancer, the data indicates that this extensively characterized protein may have a novel function in the nucleus of prostate epithelial cells.

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.