A novel human tocopherol-associated protein: cloning, in vitro expression, and characterization

Circuit-wide proteomics profiling reveals brain region-specific protein signatures in the male WKY rats with endogenous depression

BACKGROUND

Although the Wistar Kyoto (WKY) rat has been consistently recognized as an animal model with endogenous depression, the exact molecular mechanisms underlying its genetic susceptibility to depression remain undetermined.

METHODS

Compared with the Wistar rats, the depression-like behaviors of the male WKY ones were evaluated by both the sucrose preference test and forced swimming test. Golgi staining analysis was conducted to access the dendritic morphology. TMT-labelled quantitative proteomics analyses were respectively performed in the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), and hippocampus (Hip), followed by KEGG enrichment-based clustering analysis, Venn diagram analysis, and Pearson correlation analysis.

RESULTS

The WKY strain showed significant differences in both the depression-like behaviors and synaptic plasticity. Moreover, the WKY model displayed markedly distinct differentially-expressed protein (DEP) profiles, with minor differences between the WKY subgroups. A cerebral regional commonality and specificity were evident in the signaling pathways enriched in the WKY model, and a total of 15 brain region-specific DEPs were identified to closely correlate with the depression-like phenotypes (in the mPFC: Lrrc8d, Dcun1d2, and Mtnd5; in the NAc: Ccdc154, Sec14l2, Kif2a, LOC680322, Me1, Mknk1, and Ret7; in the Hip: Sec14l2, Serpinf2, LOC103694855, Fam13c, and Loxl1). Data were available via ProteomeXchange with identifier PXD029079.

LIMITATIONS

Female WKY rats are not included, and the roles of these candidate DEPs in depression remain further elucidation.

CONCLUSION

The present study further evidences the brain region-specific protein signatures in the male WKY model with endogenous depression, providing novel insights into the pathogenesis of depression in males.

Supplementation With Carotenoids, Omega-3 Fatty Acids, and Vitamin E Has a Positive Effect on the Symptoms and Progression of Alzheimer’s Disease

Background: Preliminary work by our center has reported behavior and functional benefits in patients with Alzheimer’s disease (AD) following targeted micronutritional supplementation. Objective: To build on the existing exploratory research and investigate the impact of these micronutrients on the natural progression of AD in a randomized controlled trial. Methods: Patients with mild-moderate AD consumed daily 1 g fish oil (of which 500 mg DHA, 150 mg EPA), 22 mg carotenoids (10 mg lutein, 10 mg meso-zeaxanthin, 2 mg zeaxanthin), and 15 mg vitamin E or placebo for 12 months in a double-blind, placebo-controlled, randomized clinical trial. Carotenoids, ω-3FAs, and vitamin E were quantified in blood. Carotenoids were also measured in skin. AD severity was measured using the mini-mental state examination and dementia severity rating scale tools. Behavior, mood, and memory were measured using an informant-based questionnaire. Results: Following 12 months of supplementation, the active group (n = 50) compared to the placebo group (n = 27), demonstrated statistically significant improvements in skin carotenoid measurements, blood carotenoids, ω-3FAs, and vitamin E concentrations (p <  0.05, for all). The active group also performed better in objective measures of AD severity (i.e., memory and mood), with a statistically significant difference reported in the clinical collateral for memory (p <  0.001). Conclusion: Exponential increases in the prevalence of AD and its relentless progressive nature is driving the need for interventions that help to ameliorate symptoms and improve quality of life in AD patients. Given the positive outcomes demonstrated in this trial, this combined micronutrient dietary supplement should be considered in the overall management of AD.

[Physiological Function and Congenital Deficiency of α-TTP, a Determinant of Vitamin E Transport in the Body -One Portion of the Research for Which the Pharmaceutical Society of Japan Award Was Given]

This review summarizes one portion of the research for which the author received the Pharmaceutical Society of Japan Award. The complete title of the awarded research is "Pharmacological Studies on Metabolism and Functions of Biomembrane Lipids". Because the awarded research is a very broad study, this review describes the discovery, physiological functions, and congenital defects of α-tocopherol transfer protein (α-TTP), a critical factor in determining the transport of vitamin E in the body, which has been the focus of the author's work throughout his research career.

Identification of SEC14 like lipid binding 2(SEC14L2) sequence and expression profiles in the Chinese tree shrew (Tupaia belangeri chinensis)

BACKGROUND

The product of the SEC14L2 (SEC14 Like Lipid Binding 2) gene belongs to a family of lipid-binding proteins including Sec14p, alpha-tocopherol transfer protein, and cellular retinol-binding protein. SEC14L2 expression enables replication of clinical hepatitis C virus (HCV) isolates in several hepatoma cell lines, and mutations in SEC14L2 may enhance HCV replication in vitro. The Chinese tree shrew (Tupaia belangeri chinensis) is a potential animal model for studying HCV replication, however, the cDNA sequence, protein structure, and expression of the Chinese tree shrew SEC14L2 gene have yet to be characterized.

METHODS AND RESULTS

In the present study, we cloned the full-length cDNA sequence of the SEC14L2 in the Chinese tree shrew by using rapid amplification of cDNA ends technology. This led us to determine that, this is 2539 base pairs (bp) in length, the open reading frame sequence is 1212 bp, and encodes 403 amino acids. Following this, we constructed a phylogenetic tree based on SEC14L2 molecules from various species and compared SEC14L2 amino acid sequence with other species. This analysis indicated that the Chinese tree shrew SEC14L2 protein (tsSEC14L2) has 96.28% amino acid similarity to the human protein, and is more closely related to the human protein than either mouse or rat protein. The Chinese tree shrew SEC14L2 mRNA was detected in all tissues, and showed highest expression levels in the pancreas, small intestine and trachea, however the tsSEC14L2 protein abundance was highest in the liver and small intestine.

CONCLUSION

The Chinese tree shrew SEC14L2 gene was closer in evolutionary relation to humans and non-human primates and expression of the tsSEC14L2 protein was highest in the liver and small intestine. These results may provide useful information for tsSEC14L2 function in HCV infection.

Molecular Mechanisms Underlying the Therapeutic Role of Vitamin E in Age-Related Macular Degeneration

The eye is particularly susceptible to oxidative stress and disruption of the delicate balance between oxygen-derived free radicals and antioxidants leading to many degenerative diseases. Attention has been called to all isoforms of vitamin E, with α-tocopherol being the most common form. Though similar in structure, each is diverse in antioxidant activity. Preclinical reports highlight vitamin E’s influence on cell physiology and survival through several signaling pathways by activating kinases and transcription factors relevant for uptake, transport, metabolism, and cellular action to promote neuroprotective effects. In the clinical setting, population-based studies on vitamin E supplementation have been inconsistent at times and follow-up studies are needed. Nonetheless, vitamin E’s health benefits outweigh the controversies. The goal of this review is to recognize the importance of vitamin E’s role in guarding against gradual central vision loss observed in age-related macular degeneration (AMD). The therapeutic role and molecular mechanisms of vitamin E’s function in the retina, clinical implications, and possible toxicity are collectively described in the present review.

Immune Cell Infiltration and Relevant Gene Signatures in the Tumor Microenvironment that Significantly Associates With the Prognosis of Patients With Breast Cancer

Breast cancer is the most common malignancy and the leading cause of cancer-related deaths in women. Recent studies have investigated the prognostic value of the tumor microenvironment (TME)-related genes in breast cancer. The purpose of this research is to identify the immune-associated prognostic signature for breast cancer evaluate the probability of their prognostic value and compare the current staging system. In this study, we comprehensively evaluated the infiltration patterns of TME in 1,077 breast cancer patients downloaded from TCGA by applying the ssGSEA method to the transcriptome of these patients. Thus, generated two groups of immune cell infiltration. Based on two groups of low infiltration and high infiltration immune cell groups, 983 common differentially expressed genes were found using the limma algorithm. In addition, studying potential mechanisms, the GSEA method was used to indicate some pathways with remarkable enrichment in two clusters of immune cell infiltration. Finally, the seven immune-associated hub genes with survival as prognostic signatures were identified by using univariate Cox, survival, and LASSO analyses and constructed a TME score. The prognostic value of the TME score was self-validated in the TCGA cohort and further validated in an external independent set from METABRIC and GEO database by time-dependent survival receiver operation. Univariate and multivariate analyses of clinicopathological characteristics indicated that the TME score was an independent prognostic factor. In conclusion, the proposed TME score model should be considered as a prognostic factor, similar to the current TNM stage, and the seven immune-related genes can be a valuable potential biomarker for breast cancer.

α-Tocopherol transfer protein (α-TTP)

α-Tocopherol transfer protein (α-TTP) is so far the only known protein that specifically recognizes α-tocopherol (α-Toc), the most abundant and most biologically active form of vitamin E, in higher animals. α-TTP is highly expressed in the liver where α-TTP selects α-Toc among vitamin E forms taken up via plasma lipoproteins and promotes its secretion to circulating lipoproteins. Thus, α-TTP is a major determinant of plasma α-Toc concentrations. Familial vitamin E deficiency, also called Ataxia with vitamin E deficiency, is caused by mutations in the α-TTP gene. More than 20 different mutations have been found in the α-TTP gene worldwide, among which some missense mutations provided valuable clues to elucidate the molecular mechanisms underlying intracellular α-Toc transport. In hepatocytes, α-TTP catalyzes the vectorial transport of α-Toc from the endocytotic compartment to the plasma membrane (PM) by targeting phosphatidylinositol phosphates (PIPs) such as PI(4,5)P₂. By binding PIPs at the PM, α-TTP opens the lid covering the hydrophobic pocket, thus facilitating the release of bound α-Toc to the PM.

Reflections on a century of vitamin E research: Looking at the past with an eye on the future

The name vitamin E, was given by Barnett and Sure who suggested that the factor proposed by Evans and Bishop as substance "X," be termed vitamin "E" as the next vitamin after the A, B, C and D vitamins had been already described. The identification of vitamin E with a-tocopherol was made in 1936 by Evans' group. One year later β-tocopherol and 11 years later δ-tocopherol were isolated. Tocotrienol (named zetatocopherol) was first described in 1957 and later isolated in 1961. The antioxidant property of tocopherols was reported by Olcott and Emerson in 1937. Inherited vitamin E deficiency, AVED, characterized by a form of neuromyopathy was first described in 1981. The disease, was localized to chromosome 8q and found to be caused by a mutation of the a-TTP gene. The subsequent paragraphs are not a comprehensive review but only critical reflections on some important aspects of vitamin E research.

A Golgi-derived vesicle potentiates PtdIns4P to PtdIns3P conversion for endosome fission

Endosome fission is essential for cargo sorting and targeting in the endosomal system. However, whether organelles other than the endoplasmic reticulum (ER) participate in endosome fission through membrane contacts is unknown. Here, we characterize a Golgi-derived vesicle, the SEC14L2 compartment, that plays a unique role in facilitating endosome fission through ternary contacts with endosomes and the ER. Localized to the ER-mediated endosome fission site, the phosphatidylinositol transfer protein SEC14L2 promotes phosphatidylinositol 4-phosphate (PtdIns4P) to phosphatidylinositol 3-phosphate (PtdIns3P) conversion before endosome fission. In the absence of SEC14L2, endosome fission is attenuated and more enlarged endosomes arise due to endosomal accumulation of PtdIns4P and reduction in PtdIns3P. Collectively, our data suggest roles of the Golgi network in ER-associated endosome fission and a mechanism involving ER-endosome contacts in the regulation of endosomal phosphoinositide conversion.

The Physiological Roles of Vitamin E and Hypovitaminosis E in the Transition Period of High-Yielding Dairy Cows

Simple Summary

In high-yield cows, most production diseases occur during transition periods. Alpha-tocopherol, the most biologically active form of vitamin E, declines in blood and reaches the lowest levels (hypovitaminosis E) around calving. Hypovitaminosis E is associated with the incidence of peripartum diseases. Therefore, many studies which have been published for more than 30 years have investigated the effects of α-tocopherol supplementation. This α-tocopherol deficiency was thought to be caused by complex factors. However, until recently, the physiological factors or pathways underlying hypovitaminosis E in the transition period have been poorly understood. In the last 10 years, the α-tocopherol-related genes expression, which regulate the metabolism, transportation, and tissue distribution of α-tocopherol in humans and rodents, has been reported in ruminant tissues. In this paper, we discuss at least six physiological phenomena that occur during the transition period and may be candidate factors predisposing to a decreased blood α-tocopherol level and hypovitaminosis E with changes in α-tocopherol-related genes expression.

Abstract

Levels of alpha-tocopherol (α-Toc) decline gradually in blood throughout prepartum, reaching lowest levels (hypovitaminosis E) around calving. Despite numerous reports about the disease risk in hypovitaminosis E and the effect of α-Toc supplementation on the health of transition dairy cows, its risk and supplemental effects are controversial. Here, we present some novel data about the disease risk of hypovitaminosis E and the effects of α-Toc supplementation in transition dairy cows. These data strongly demonstrate that hypovitaminosis E is a risk factor for the occurrence of peripartum disease. Furthermore, a study on the effectiveness of using serum vitamin levels as biomarkers to predict disease in dairy cows was reported, and a rapid field test for measuring vitamin levels was developed. By contrast, evidence for how hypovitaminosis E occurred during the transition period was scarce until the 2010s. Pioneering studies conducted with humans and rodents have identified and characterised some α-Toc-related proteins, molecular players involved in α-Toc regulation followed by a study in ruminants from the 2010s. Based on recent literature, the six physiological factors: (1) the decline in α-Toc intake from the close-up period; (2) changes in the digestive and absorptive functions of α-Toc; (3) the decline in plasma high-density lipoprotein as an α-Toc carrier; (4) increasing oxidative stress and consumption of α-Toc; (5) decreasing hepatic α-Toc transfer to circulation; and (6) increasing mammary α-Toc transfer from blood to colostrum, may be involved in α-Toc deficiency during the transition period. However, the mechanisms and pathways are poorly understood, and further studies are needed to understand the physiological role of α-Toc-related molecules in cattle. Understanding the molecular mechanisms underlying hypovitaminosis E will contribute to the prevention of peripartum disease and high performance in dairy cows.

Alpha-Tocopherol Metabolites (the Vitamin E Metabolome) and Their Interindividual Variability during Supplementation

The metabolism of α-tocopherol (α-TOH, vitamin E) shows marked interindividual variability, which may influence the response to nutritional and therapeutic interventions with this vitamin. Recently, new metabolomics protocols have fostered the possibility to explore such variability for the different metabolites of α-TOH so far identified in human blood, i.e., the “vitamin E metabolome”, some of which have been reported to promote important biological functions. Such advances prompt the definition of reference values and degree of interindividual variability for these metabolites at different levels of α-TOH intake. To this end, a one-week oral administration protocol with 800 U RRR-α-TOH/day was performed in 17 healthy volunteers, and α-TOH metabolites were measured in plasma before and at the end of the intervention utilizing a recently validated LC-MS/MS procedure; the expression of two target genes of α-TOH with possible a role in the metabolism and function of this vitamin, namely pregnane X receptor (PXR) and the isoform 4F2 of cytochrome P450 (CYP4F2) was assessed by immunoblot in peripheral blood leukocytes. The levels of enzymatic metabolites showed marked interindividual variability that characteristically increased upon supplementation. With the exception of α-CEHC (carboxy-ethyl-hydroxychroman) and the long-chain metabolites M1 and α-13′OH, such variability was found to interfere with the possibility to utilize them as sensitive indicators of α-TOH intake. On the contrary, the free radical-derived metabolite α-tocopheryl quinone significantly correlated with the post-supplementation levels of α-TOH. The supplementation stimulated PXR, but not CYP4F2, expression of leucocytes, and significant correlations were observed between the baseline levels of α-TOH and both the baseline and post-supplementation levels of PXR. These findings provide original analytical and molecular information regarding the human metabolism of α-TOH and its intrinsic variability, which is worth considering in future nutrigenomics and interventions studies.

Invisible leashes: The tethering VAPs from infectious diseases to neurodegeneration

Intracellular organelles do not, as thought for a long time, act in isolation but are dynamically tethered together by entire machines responsible for interorganelle trafficking and positioning. Among the proteins responsible for tethering is the family of VAMP-associated proteins (VAPs) that appear in all eukaryotes and are localized primarily in the endoplasmic reticulum. The major functional role of VAPs is to tether the endoplasmic reticulum with different organelles and regulate lipid metabolism and transport. VAPs have gained increasing attention because of their role in human pathology where they contribute to infections by viruses and bacteria and participate in neurodegeneration. In this review, we discuss the structure, evolution, and functions of VAPs, focusing more specifically on VAP-B for its relationship with amyotrophic lateral sclerosis and other neurodegenerative diseases.

The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates

Vitamin A is an essential nutrient necessary for numerous basic physiological functions, including reproduction and development, immune cell differentiation and communication, as well as the perception of light. To evade the dire consequences of vitamin A deficiency, vertebrates have evolved specialized metabolic pathways that enable the absorption, transport, and storage of vitamin A acquired from dietary sources as preformed retinoids or provitamin A carotenoids. This evolutionary advantage requires a complex interplay between numerous specialized retinoid-transport proteins, receptors, and enzymes. Recent advances in molecular and structural biology resulted in a rapid expansion of our understanding of these processes at the molecular level. This progress opened new avenues for the therapeutic manipulation of retinoid homeostasis. In this review, we summarize current research related to the biochemistry of carotenoid and retinoid-processing proteins with special emphasis on the structural aspects of their physiological actions. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Genome-wide association analysis of natural variation in seed tocochromanols of barley

Tocochromanols (tocols for short), commonly called Vitamin E, are lipid-soluble plant antioxidants vital for regulating lipid peroxidation in chloroplasts and seeds. Barley (Hordeum vulgare L.) seeds contain all eight different isoforms of tocols; however, the extent of natural variation in their composition and their underlying genetic basis is not known. Tocol levels in barley seeds were quantified in diverse H. vulgare panels comprising 297 wild lines from a diversity panel and 160 cultivated spring-type accessions from the mini-core panel representing the genetic diversity of the USDA barley germplasm collection. Significant differences were observed in the concentration of tocols between the two panels. To identify the genes associated with tocols, genome-wide association analysis was conducted with single nucleotide polymorphisms (SNPs) from Illumina arrays for the mini-core panel and genotyping-by-sequencing for the wild barley panel. Forty unique SNPs in the wild barley and 27 SNPs in the mini-core panel were significantly associated with various tocols. Marker-trait associations (MTAs) were identified on chromosomes 1, 6, and 7 for key genes in the tocol biosynthesis pathway, which have also been reported in other studies. Several novel MTAs were identified on chromosomes 2, 3, 4 and 5 and were found to be in proximity to genes involved in the generation of precursor metabolites required for tocol biosynthesis. This study provides a valuable resource for barley breeding programs targeting specific isoforms of seed tocols and for investigating the physiological roles of these metabolites in seed longevity, dormancy, and germination.

Molecular Understanding of the Cardiomodulation in Myocardial Infarction and the Mechanism of Vitamin E Protections

:

Myocardial infarction is a major cause of deaths globally. Modulation of several molecular mechanisms occurs during the initial stages of myocardial ischemia prior to permanent cardiac tissue damage, which involves both pathogenic as well as survival pathways in the cardiomyocyte. Currently, there is increasing evidence regarding the cardioprotective role of vitamin E in alleviating the disease. This fat-soluble vitamin does not only act as a powerful antioxidant; but it also has the ability to regulate several intracellular signalling pathways including HIF-1, PPAR-γ, Nrf-2, and NF-κB that influence the expression of a number of genes and their protein products. Essentially, it inhibits the molecular progression of tissue damage and preserves myocardial tissue viability. This review aims to summarize the molecular understanding of the cardiomodulation in myocardial infarction as well as the mechanism of vitamin E protection.

Effects of dietary RRR α-tocopherol vs all-racemic α-tocopherol on health outcomes

Of the 8 vitamin E analogues, RRR α-tocopherol likely has the greatest effect on health outcomes. Two sources of α-tocopherol, naturally sourced RRR α-tocopherol and synthetic all-racemic α-tocopherol, are commonly consumed from foods and dietary supplements in the United States. A 2016 US Food and Drug Administration ruling substantially changed the RRR to all-racemic α-tocopherol ratio of biopotency from 1.36:1 to 2:1 for food-labeling purposes, but the correct ratio is still under debate in the literature. Few studies have directly compared the 2 α-tocopherol sources, and existing studies do not compare the efficacy of either source for preventing or treating disease in humans. To help close this gap, this review evaluates studies that investigated the effects of either RRR α-tocopherol or all-racemic α-tocopherol on health outcomes, and compares the overall findings. α-Tocopherol has been used to prevent and/or treat cancer and diseases of the central nervous system, the immune system, and the cardiovascular system, so these diseases are the focus of the review. No firm conclusions about the relative effects of the α-tocopherol sources on health outcomes can be made. Changes to α-tocopherol-relevant policies have proceeded without adequate scientific support. Additional research is needed to assemble the pieces of the α-tocopherol puzzle and to determine the RRR to all-racemic α-tocopherol ratio of biopotency for health outcomes.

SEC14L2, a lipid-binding protein, regulates HCV replication in culture with inter- and intra-genotype variations

BACKGROUND & AIMS

The lipid-binding protein, SEC14L2, is crucial for the efficient viral replication of clinical hepatitis C virus (HCV) isolates in cell culture. Given the role of SEC14L2 in HCV replication, we aimed to study a large number of HCV positive sera carrying genotypes 1-4, to identify viral factors associated with efficient replication in culture. Additionally, we investigated whether 13 single nucleotide polymorphisms (SNPs) of SEC14L2 have an impact on RNA replication of naturally occurring HCV isolates.

METHODS

We generated Huh-7.5 cell lines overexpressing SEC14L2 or 13 coding SNPs and tested 73 different HCV positive sera for in vitro replication. Furthermore, we genotyped a cohort of 262 patients with chronic HCV for the common SNP (rs757660) and investigated its effect on the clinical phenotype.

RESULTS

HCV isolates from genotype 1, 2, 3 and 4 replicate in Huh-7.5 cells overexpressing SEC14L2. Interestingly, only subgenomic replicons from genotypes 1 and 3 showed enhanced replication whereas genotypes 2 and 4 remained unaffected. Furthermore, replication was independent of viral load. Importantly, all tested SNPs supported HCV RNA replication in vitro, while 1 SNP was associated with decreased SEC1L2 expression and viral RNA. All SNPs exhibited comparable cellular cholesterol and vitamin E abundance in naïve Huh-7.5 cells.

CONCLUSIONS

This large screen of natural HCV isolates of 4 genotypes underscores the relevance of SEC14L2 as an in vitro HCV host factor. Additionally, SEC14L2 variants appear to recapitulate the wild-type enhancement of HCV replication. Variant rs191341134 showed a decreased effect due to lowered stability, whereas variant rs757660, a high prevalence mutant, showed a similar phenotype to the wild-type.

LAY SUMMARY

Until the year 2015, consistent replication of patient-derived isolates of hepatitis C virus (HCV) in an in vitro model remained a limitation in HCV research. In 2015 a group of authors identified a protein named SEC14L2 that enabled the replication of HCV isolates in cell culture. We performed a large screen encompassing 73 isolates of 4 different HCV genotypes. Additionally, we replaced the natural SEC14L2 with 13 different mutants to test if the protein variation significantly altered its HCV replication enhancing functions. We showed that different genotypes of HCV react differently to the presence of this protein and the variants of the protein mimic the behavior of the wild-type.

A Drosophila genetic screen for suppressors of S6kinase-dependent growth identifies the F-box subunit Archipelago/FBXW7

This study was designed to identify novel negative regulators of the Drosophila S6kinase (dS6K). S6K is a downstream effector of the growth-regulatory complex mTORC1 (mechanistic-Target-of-Rapamycin complex 1). Nutrients activate mTORC1, which in turn induces the phosphorylation of S6K to promote cell growth, whereas fasting represses mTORC1 activity. Here, we screened 11,000 RNA-interfering (RNAi) lines and retained those that enhanced a dS6K-dependent growth phenotype. Since RNAi induces gene knockdown, enhanced tissue growth supports the idea that the targeted gene acts as a growth suppressor. To validate the resulting candidate genes, we monitored dS6K phosphorylation and protein levels in double-stranded RNAi-treated S2 cells. We identified novel dS6K negative regulators, including gene products implicated in basal cellular functions, suggesting that feedback inputs modulate mTORC1/dS6K signaling. We also identified Archipelago (Ago), the Drosophila homologue of FBXW7, which is an E3-ubiquitin-ligase subunit that loads ubiquitin units onto target substrates for proteasome-mediated degradation. Despite a previous report showing an interaction between Ago/FBXW7 and dS6K in a yeast two-hybrid assay and the presence of an Ago/FBXW7-consensus motif in the dS6K polypeptide, we could not see a direct interaction in immunoprecipitation assay. Nevertheless, we observed that loss-of-ago/fbxw7 in larvae resulted in an increase in dS6K protein levels, but no change in the levels of phosphorylated dS6K or dS6K transcripts, suggesting that Ago/FBXW7 indirectly controls dS6K translation or stability. Through the identification of novel negative regulators of the downstream target, dS6K, our study may help deciphering the underlying mechanisms driving deregulations of mTORC1, which underlies several human diseases.

Vitamin E Metabolic Effects and Genetic Variants: A Challenge for Precision Nutrition in Obesity and Associated Disturbances

Vitamin E (VE) has a recognized leading role as a contributor to the protection of cell constituents from oxidative damage. However, evidence suggests that the health benefits of VE go far beyond that of an antioxidant acting in lipophilic environments. In humans, VE is channeled toward pathways dealing with lipoproteins and cholesterol, underlining its relevance in lipid handling and metabolism. In this context, both VE intake and status may be relevant in physiopathological conditions associated with disturbances in lipid metabolism or concomitant with oxidative stress, such as obesity. However, dietary reference values for VE in obese populations have not yet been defined, and VE supplementation trials show contradictory results. Therefore, a better understanding of the role of genetic variants in genes involved in VE metabolism may be crucial to exert dietary recommendations with a higher degree of precision. In particular, genetic variability should be taken into account in targets concerning VE bioavailability per se or concomitant with impaired lipoprotein transport. Genetic variants associated with impaired VE liver balance, and the handling/resolution of oxidative stress might also be relevant, but the core information that exists at present is insufficient to deliver precise recommendations.

Cellular Uptake and Bioavailability of Tocotrienol-Rich Fraction in SIRT1-Inhibited Human Diploid Fibroblasts

Tocotrienol-rich fraction (TRF) is palm vitamin E that consists of tocopherol and tocotrienol. TRF is involved in important cellular regulation including delaying cellular senescence. A key regulator of cellular senescence, Sirtuin 1 (SIRT1) is involved in lipid metabolism. Thus, SIRT1 may regulate vitamin E transportation and bioavailability at cellular level. This study aimed to determine the role of SIRT1 on cellular uptake and bioavailability of TRF in human diploid fibroblasts (HDFs). SIRT1 gene in young HDFs was silenced by small interference RNA (siRNA) while SIRT1 activity was inhibited by sirtinol. TRF treatment was given for 24 h before or after SIRT1 inhibition. Cellular concentration of TRF isomers was determined according to the time points of before and after TRF treatment at 0, 24, 48, 72 and 96 h. Our results showed that all tocotrienol isomers were significantly taken up by HDFs after 24 h of TRF treatment and decreased 24 h after TRF treatment was terminated but remained in the cell up to 72 h. The uptake of α-tocopherol, α-tocotrienol and β-tocotrienol was significantly higher in senescent cells as compared to young HDFs indicating higher requirement for vitamin E in senescent cells. Inhibition of SIRT1 gene increased the uptake of all tocotrienol isomers but not α-tocopherol. However, SIRT1 inhibition at protein level decreased tocotrienol concentration. In conclusion, SIRT1 may regulate the cellular uptake and bioavailability of tocotrienol isomers in human diploid fibroblast cells while a similar regulation was not shown for α-tocopherol.

α-Tocopherol succinate enhances pterostilbene anti-tumor activity in human breast cancer cells in vivo and in vitro

Vitamin E (Vit. E) is considered an essential dietary nutrient for humans and animals. An enormous body of evidence indicates the biological and protective effects of Vit. E consumption. Tocopherol-associated protein (TAP) is a major tocopherol-binding protein affecting Vit. E stimulation and downstream signaling transduction. However, how Vit. E utilizes TAP as an anti-cancer mechanism remains unclear. Microarray analysis of signature gene profiles in breast cancer cells treated with α-tocopheryl succinate (α-TOS, a Vit. E isoform) resulted in cell cycle arrest and anti-cancer activity in breast cancer cells. Pterostilbene (PS), a natural dietary antioxidant found in blueberries, in combination with α-TOS synergistically maximized breast cancer cell growth inhibition by disrupting signal transduction, transcription factors and cell cycle proteins. In a xenograft mouse model, PS treatment with Vit. E inhibited breast tumor growth and cell invasion, which were evaluated using our recently developed circulating tumor cell (CTC) detection assay. Because dietary Vit. E and PS supplementation contributed to preventative and therapeutic effects in vitro and in vivo, this combination may benefit breast cancer therapy in the clinic.

The Subcellular Distribution of Alpha-Tocopherol in the Adult Primate Brain and Its Relationship with Membrane Arachidonic Acid and Its Oxidation Products

The relationship between α-tocopherol, a known antioxidant, and polyunsaturated fatty acid (PUFA) oxidation, has not been directly investigated in the primate brain. This study characterized the membrane distribution of α-tocopherol in brain regions and investigated the association between membrane α-tocopherol and PUFA content, as well as brain PUFA oxidation products. Nuclear, myelin, mitochondrial, and neuronal membranes were isolated using a density gradient from the prefrontal cortex (PFC), cerebellum (CER), striatum (ST), and hippocampus (HC) of adult rhesus monkeys (n = 9), fed a stock diet containing vitamin E (α-, γ-tocopherol intake: ~0.7 µmol/kg body weight/day, ~5 µmol/kg body weight/day, respectively). α-tocopherol, PUFAs, and PUFA oxidation products were measured using high performance liquid chromatography (HPLC), gas chromatography (GC) and liquid chromatography-gas chromatography/mass spectrometry (LC-GC/MS) respectively. α-Tocopherol (ng/mg protein) was highest in nuclear membranes (p < 0.05) for all regions except HC. In PFC and ST, arachidonic acid (AA, µg/mg protein) had a similar membrane distribution to α-tocopherol. Total α-tocopherol concentrations were inversely associated with AA oxidation products (isoprostanes) (p < 0.05), but not docosahexaenoic acid oxidation products (neuroprostanes). This study reports novel data on α-tocopherol accumulation in primate brain regions and membranes and provides evidence that α-tocopherol and AA are similarly distributed in PFC and ST membranes, which may reflect a protective effect of α-tocopherol against AA oxidation.

Vitamin E Bioavailability: Mechanisms of Intestinal Absorption in the Spotlight

Vitamin E is an essential fat-soluble micronutrient whose effects on human health can be attributed to both antioxidant and non-antioxidant properties. A growing number of studies aim to promote vitamin E bioavailability in foods. It is thus of major interest to gain deeper insight into the mechanisms of vitamin E absorption, which remain only partly understood. It was long assumed that vitamin E was absorbed by passive diffusion, but recent data has shown that this process is actually far more complex than previously thought. This review describes the fate of vitamin E in the human gastrointestinal lumen during digestion and focuses on the proteins involved in the intestinal membrane and cellular transport of vitamin E across the enterocyte. Special attention is also given to the factors modulating both vitamin E micellarization and absorption. Although these latest results significantly improve our understanding of vitamin E intestinal absorption, further studies are still needed to decipher the molecular mechanisms driving this multifaceted process.

Many tocopherols, one vitamin E

Four tocopherols are available in nature and are absorbed with the diet, but only one RRR-α-tocopherol satisfies the criteria of being a vitamin. The biological activity of the different tocopherols studied in the rat by the resorption-gestation test has been inconsistently extrapolated to human beings where the tocopherols have no influence on a successful pregnancy. Diminution of RRR-α-tocopherol intake results in diseases characterized by ataxia, whose pathogenetic mechanism, despite vigorous claims, has not been clarified. The calculation of the Daily Reference Intake (DRI), necessary to prevent disease, is based on an obsolete test, the peroxide-induced erythrocyte hemolysis, called the gold standard, but of highly questioned validity. If many epidemiological studies have given positive results, showing prevention by high vitamin E containing diets of cardiovascular events, neurodegenerative disease, macular degeneration and cancer, the clinical confirmatory intervention studies were mostly negative. On the positive side, besides preventing vitamin E deficiency diseases, vitamin E has shown efficacy as anti-inflammatory and immune boosting compound. It has also shown some efficacy in protecting against nonalcoholic hepato-steatosis. At a molecular level, vitamin E and some of its metabolites have shown capacity of regulating cell signaling and modulating gene transcription.

Pulmonary microRNA profiles identify involvement of Creb1 and Sec14l3 in bronchial epithelial changes in allergic asthma

Asthma is highly prevalent, but current therapies cannot influence the chronic course of the disease. It is thus important to understand underlying early molecular events. In this study, we aimed to use microRNAs (miRNAs) - which are critical regulators of signaling cascades - to identify so far uncharacterized asthma pathogenesis pathways. Therefore, deregulation of miRNAs was assessed in whole lungs from mice with ovalbumin (OVA)-induced allergic airway inflammation (AAI). In silico predicted target genes were confirmed in reporter assays and in house-dust-mite (HDM) induced AAI and primary human bronchial epithelial cells (NHBE) cultured at the air-liquid interface. We identified and validated the transcription factor cAMP-responsive element binding protein (Creb1) and its transcriptional co-activators (Crtc1-3) as targets of miR-17, miR-144, and miR-21. Sec14-like 3 (Sec14l3) - a putative target of Creb1 - was down-regulated in both asthma models and in NHBE cells upon IL13 treatment, while it’s expression correlated with ciliated cell development and decreased along with increasing goblet cell metaplasia. Finally, we propose that Creb1/Crtc1-3 and Sec14l3 could be important for early responses of the bronchial epithelium to Th2-stimuli. This study shows that miRNA profiles can be used to identify novel targets that would be overlooked in mRNA based strategies.

Vitamin E: Emerging aspects and new directions

The discovery of vitamin E will have its 100th anniversary in 2022, but we still have more questions than answers regarding the biological functions and the essentiality of vitamin E for human health. Discovered as a factor essential for rat fertility and soon after characterized for its properties of fat-soluble antioxidant, vitamin E was identified to have signaling and gene regulation effects in the 1980s. In the same years the cytochrome P-450 dependent metabolism of vitamin E was characterized and a first series of studies on short-chain carboxyethyl metabolites in the 1990s paved the way to the hypothesis of a biological role for this metabolism alternative to vitamin E catabolism. In the last decade other physiological metabolites of vitamin E have been identified, such as α-tocopheryl phosphate and the long-chain metabolites formed by the ω-hydroxylase activity of cytochrome P-450. Recent findings are consistent with gene regulation and homeostatic roles of these metabolites in different experimental models, such as inflammatory, neuronal and hepatic cells, and in vivo in animal models of acute inflammation. Molecular mechanisms underlying these responses are under investigation in several laboratories and side-glances to research on other fat soluble vitamins may help to move faster in this direction. Other emerging aspects presented in this review paper include novel insights on the mechanisms of reduction of the cardiovascular risk, immunomodulation and antiallergic effects, neuroprotection properties in models of glutamate excitotoxicity and spino-cerebellar damage, hepatoprotection and prevention of liver toxicity by different causes and even therapeutic applications in non-alcoholic steatohepatitis. We here discuss these topics with the aim of stimulating the interest of the scientific community and further research activities that may help to celebrate this anniversary of vitamin E with an in-depth knowledge of its action as vitamin.

The naturally occurring α-tocopherol stereoisomer RRR-α-tocopherol is predominant in the human infant brain

α-Tocopherol is the principal source of vitamin E, an essential nutrient that plays a crucial role in maintaining healthy brain function. Infant formula is routinely supplemented with synthetic α-tocopherol, a racaemic mixture of eight stereoisomers with less bioactivity than the natural stereoisomer RRR-α-tocopherol. α-Tocopherol stereoisomer profiles have not been previously reported in the human brain. In the present study, we analysed total α-tocopherol and α-tocopherol stereoisomers in the frontal cortex (FC), hippocampus (HPC) and visual cortex (VC) of infants (n 36) who died of sudden infant death syndrome or other conditions. RRR-α-tocopherol was the predominant stereoisomer in all brain regions (P<0·0001) and samples, despite a large intra-decedent range in total α-tocopherol (5–17 μg/g). Mean RRR-α-tocopherol concentrations in FC, HPC and VC were 10·5, 6·8 and 5·5 μg/g, respectively. In contrast, mean levels of the synthetic stereoisomers were RRS, 1–1·5; RSR, 0·8–1·0; RSS, 0·7–0·9; and Σ2S 0·2–0·3 μg/g. Samples from all but two decedents contained measurable levels of the synthetic stereoisomers, but the intra-decedent variation was large. The ratio of RRR:the sum of the synthetic 2R stereoisomers (RRS+RSR+RSS) averaged 2·5, 2·3 and 2·4 in FC, HPC and VC, respectively, and ranged from 1 to at least 4·7, indicating that infant brain discriminates against synthetic 2R stereoisomers in favour of RRR. These findings reveal that RRR-α-tocopherol is the predominant stereoisomer in infant brain. These data also indicate that the infant brain discriminates against the synthetic 2R stereoisomers, but is unable to do so completely. On the basis of these findings, investigation into the impact of α-tocopherol stereoisomers on neurodevelopment is warranted.

Sec14-like phosphatidylinositol transfer proteins and the biological landscape of phosphoinositide signaling in plants

Phosphoinositides and soluble inositol phosphates are essential components of a complex intracellular chemical code that regulates major aspects of lipid signaling in eukaryotes. These involvements span a broad array of biological outcomes and activities, and cells are faced with the problem of how to compartmentalize and organize these various signaling events into a coherent scheme. It is in the arena of how phosphoinositide signaling circuits are integrated and, and how phosphoinositide pools are functionally defined and channeled to privileged effectors, that phosphatidylinositol (PtdIns) transfer proteins (PITPs) are emerging as critical players. As plant systems offer some unique advantages and opportunities for study of these proteins, we discuss herein our perspectives regarding the progress made in plant systems regarding PITP function. We also suggest interesting prospects that plant systems hold for interrogating how PITPs work, particularly in multi-domain contexts, to diversify the biological outcomes for phosphoinositide signaling. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.

Expression of a-Tocopherol-Associated protein (TAP) is associated with clinical outcome in breast cancer patients

BACKGROUND

The role of vitamin E in breast cancer prevention and treatment has been widely investigated, and the different tocopherols that comprise this nutrient have been shown to have divergent associations with cancer outcome. Our previous studies have shown that α-Tocopherol-associated protein (TAP), a vitamin E binding protein, may function as a tumor suppressor-like factor in breast carcinogenesis. The current study addresses the association of TAP expression with breast cancer clinical outcomes.

METHODS

Immunohistochemical stain for TAP was applied to a tissue microarray from a breast cancer cohort consisting of 271 patients with a median follow-up time of 5.2 years. The expression of TAP in tumor cells was compared with patient's clinical outcome at 5 years after diagnosis. The potential role of TAP in predicting outcome was also assessed in clinically relevant subsets of the cohort. In addition, we compared TAP expression and Oncotype DX scores in an independent breast cancer cohort consisting of 71 cases.

RESULTS

We demonstrate that the expression of TAP was differentially expressed within the breast cancer cohort, and that ER+/PR ± tumors were more likely to exhibit TAP expression. TAP expression was associated with an overall lower recurrence rate and a better 5-year survival rate. This association was primarily in patients with ER+ tumors; exploratory analysis showed that this association was strongest in patients with node-positive tumors and was independent of stage and treatment with chemotherapy. TAP expression in ER/PR negative or triple negative tumors had no association with clinical outcome. In addition, we did not observe an association between TAP expression and Oncotype DX recurrence score.

CONCLUSIONS

The significant positive association we found for α-Tocopherol-associated protein with outcome in breast cancer may help to better define and explain studies addressing α-tocopherol's association with cancer risk and outcome. Additionally, further studies to validate and extend these findings may allow TAP to serve as a breast-specific prognostic marker in breast cancer patients, especially in those patients with ER+ tumors.

Structural Bioinformatics Inspection of neXtProt PE5 Proteins in the Human Proteome

One goal of the Human Proteome Project is to identify at least one protein product for each of the ∼20,000 human protein-coding genes. As of October 2014, however, there are 3564 genes (18%) that have no or insufficient evidence of protein existence (PE), as curated by neXtProt; these comprise 2647 PE2-4 missing proteins and 616 PE5 dubious protein entries. We conducted a systematic examination of the 616 PE5 protein entries using cutting-edge protein structure and function modeling methods. Compared to a random sample of high-confidence PE1 proteins, the putative PE5 proteins were found to be over-represented in the membrane and cell surface proteins and peptides fold families. Detailed functional analyses show that most PE5 proteins, if expressed, would belong to transporters and receptors localized in the plasma membrane compartment. The results suggest that experimental difficulty in identifying membrane-bound proteins and peptides could have precluded their detection in mass spectrometry and that special enrichment techniques with improved sensitivity for membrane proteins could be important for the characterization of the PE5 "dark matter" of the human proteome. Finally, we identify 66 high scoring PE5 protein entries and find that six of them were reported in recent mass spectrometry databases; an illustrative annotation of these six is provided. This work illustrates a new approach to examine the potential folding and function of the dubious proteins comprising PE5, which we will next apply to the far larger group of missing proteins comprising PE2-4.

Tocopherols and tocotrienols in serum and liver of dairy cows receiving conjugated linoleic acids or a control fat supplement during early lactation

The fat-soluble vitamin E comprises the 8 structurally related compounds (congeners) α-, β-, γ-, and δ-tocopherol (with a saturated side chain) and α-, β-, γ-, and δ-tocotrienol (with a 3-fold unsaturated side chain). Little is known regarding the blood and liver concentrations of the 8 vitamin E congeners during the transition from pregnancy to lactation in dairy cows. We thus quantified tocopherols (T) and tocotrienols (T3) in serum and liver and hepatic expression of genes involved in vitamin E metabolism in pluriparous German Holstein cows during late gestation and early lactation and investigated whether dietary supplementation (from d 1 in milk) with conjugated linoleic acids (CLA; 100g/d; each 12% of trans-10,cis-12 and cis-9,trans-11 CLA; n=11) altered these compared with control-fat supplemented cows (CTR; n=10). Blood samples and liver biopsies were collected on d -21, 1, 21, 70, and 105 (liver only) relative to calving. In both groups, the serum concentrations of αT, γT, βT3, and δT3 increased from d -21 to d 21 and remained unchanged between d 21 and 70, but were unaffected by CLA. The concentrations of the different congeners of vitamin E in liver did not differ between the CTR and the CLA groups. In both groups, the concentrations of the vitamin E forms in liver changed during the course of the study. The hepatic mRNA abundance of genes controlling vitamin E status did not differ between groups, but α-tocopherol transfer protein and tocopherol-associated protein mRNA increased with time of lactation in both. In conclusion, the concentrations of vitamin E congeners and the expression of genes related to vitamin E status follow characteristic time-related changes during the transition from late gestation to early lactation but are unaffected by CLA supplementation at the dosage used.

Natural forms of vitamin E: metabolism, antioxidant, and anti-inflammatory activities and their role in disease prevention and therapy

The vitamin E family consists of four tocopherols and four tocotrienols. α-Tocopherol (αT) is the predominant form of vitamin E in tissues and its deficiency leads to ataxia in humans. However, results from many clinical studies do not support a protective role of αT in disease prevention in people with adequate nutrient status. On the other hand, recent mechanistic studies indicate that other forms of vitamin E, such as γ-tocopherol (γT), δ-tocopherol, and γ-tocotrienol, have unique antioxidant and anti-inflammatory properties that are superior to those of αT in prevention and therapy against chronic diseases. These vitamin E forms scavenge reactive nitrogen species, inhibit cyclooxygenase- and 5-lipoxygenase-catalyzed eicosanoids, and suppress proinflammatory signaling such as NF-κB and STAT3/6. Unlike αT, other vitamin E forms are significantly metabolized to carboxychromanols via cytochrome P450-initiated side-chain ω-oxidation. Long-chain carboxychromanols, especially 13'-carboxychromanols, are shown to have stronger anti-inflammatory effects than unmetabolized vitamins and may therefore contribute to the beneficial effects of vitamin E forms in vivo. Consistent with mechanistic findings, animal and human studies show that γT and tocotrienols may be useful against inflammation-associated diseases. This review focuses on non-αT forms of vitamin E with respect to their metabolism, anti-inflammatory effects and mechanisms, and in vivo efficacy in preclinical models as well as human clinical intervention studies.

Antioxidant and vitamin E transport genes and risk of high-grade prostate cancer and prostate cancer recurrence

BACKGROUND

Observational studies suggest an inverse association between vitamin E and risk of prostate cancer, particularly aggressive tumors. However, three large randomized controlled trials have reported conflicting results. Thus, we examined circulating vitamin E and vitamin E-related genes in relation to risk of high-grade prostate cancer and prostate cancer recurrence among men initially diagnosed with clinically organ-confined disease.

METHODS

We measured circulating α- and γ-tocopherol and genotyped 30 SNPs in SOD1, SOD2, SOD3, TTPA, and SEC14L2 among 573 men with organ-confined prostate cancer who underwent radical prostatectomy. We examined associations between circulating vitamin E, genotypes, and risk of high-grade prostate cancer (Gleason grade ≥ 8 or 7 with primary score ≥ 4; n = 117) using logistic regression, and risk of recurrence (56 events; 3.7 years median follow-up) using Cox proportional hazards regression.

RESULTS

Circulating γ-tocopherol was associated with an increased risk of high-grade prostate cancer (Q4 v. Q1 odds ratio [OR] = 1.87; 95% confidence intervals [CI]: 0.97-3.58; P trend =0.02). The less common allele in SOD3 rs699473 was associated with an increased risk of high-grade disease (T > C: OR = 1.40, 95% CI: 1.04-1.89). Two independent SNPs in SOD1 were inversely associated with prostate cancer recurrence in additive models (rs17884057 hazard ratio [HR] = 0.49, 95%CI: 0.25-0.96; rs9967983 HR = 0.62, 95% CI: 0.40-0.95).

CONCLUSIONS

Among men with clinically organ-confined prostate cancer, genetic variation in SOD may be associated with risk of high-grade disease at diagnosis and disease recurrence. Circulating γ-tocopherol levels may also be associated with an increased risk of high-grade disease at diagnosis.

Bioavailability of vitamin E in humans: an update

Vitamin E is essential for human health and may play a role in the prevention of some degenerative diseases. Its bioavailability, however, is wide ranging and is affected by numerous factors. Recent findings showing that the intestinal absorption of vitamin E involves proteins have raised new relevant questions about factors that can affect bioavailability. It is, therefore, opportune to present a current overview of this topic. This review begins by exploring what is known, as well as what is unknown, about the metabolization of vitamin E in the human upper gastrointestinal tract and then presents a methodical evaluation of factors assumed to affect vitamin E bioavailability. Three main conclusions can be drawn. First, the proteins ABCA1, NPC1L1, and SR-BI are implicated in the absorption of vitamin E. Second, the efficiency of vitamin E absorption is widely variable, though not accurately known (i.e., between 10% and 79%), and is affected by several dietary factors (e.g., food matrix, fat, and fat-soluble micronutrients). Finally, numerous unanswered questions remain about the metabolization of vitamin E in the intestinal lumen and about the factors affecting the efficiency of vitamin E absorption.

Genetic determinants of dietary antioxidant status

Oxidative stress refers to a physiological state in which an imbalance between pro-oxidants and antioxidants results in oxidative damage. Oxidative stress has been associated with the development of numerous chronic diseases such as type 2 diabetes, cardiovascular disease (CVD), osteoporosis, and cancer. Endogenous production of free radicals occurs during normal physiological processes, such as aerobic metabolism, oxidation of biological molecules, and enzymatic activity. Environmental factors such as ultraviolet radiation, air pollution, and cigarette smoking can also contribute to the accumulation of free radicals in the body. Excess free radicals can damage tissues and promote the upregulation of disease-related pathways such as inflammation. Modulating oxidative stress by dietary supplementation with antioxidant micronutrients such as vitamins C and E or phytochemicals such as different carotenoids may help prevent or delay the development of certain diseases. However, research on antioxidant supplementation and disease has yielded inconsistent findings, which may be due, in part, to interindividual genetic variation. Polymorphisms in genes coding for endogenous antioxidant enzymes or proteins responsible for the absorption, transport, distribution, or metabolism of dietary antioxidants have been shown to affect antioxidant status and response to supplementation. These genetic variants may also interact with environmental factors, such as diet, to determine an individual's overall antioxidant status. This chapter examines current knowledge of the relationship between genetic variation and dietary antioxidant status.

Chemopreventive activity of vitamin E in breast cancer: a focus on γ- and δ-tocopherol

Vitamin E consists of eight different variants: α-, β-, γ-, and δ-tocopherols (saturated phytyl tail) and α-, β-, γ-, and δ-tocotrienols (unsaturated phytyl tail). Cancer prevention studies with vitamin E have primarily utilized the variant α-tocopherol. To no avail, a majority of these studies focused on variant α-tocopherol with inconsistent results. However, γ-tocopherol, and more recently δ-tocopherol, have shown greater ability to reduce inflammation, cell proliferation, and tumor burden. Recent results have shown that γ-enriched mixed tocopherols inhibit the development of mammary hyperplasia and tumorigenesis in animal models. In this review, we discuss the possible differences between the variant forms, molecular targets, and cancer-preventive effects of tocopherols. We recommend that a γ-enriched mixture, γ- and δ-tocopherol, but not α-tocopherol, are promising agents for breast cancer prevention and warrant further investigation.

Vitamin E transport, membrane incorporation and cell metabolism: Is alpha-tocopherol in lipid rafts an oar in the lifeboat?

Vitamin E is composed of closely related compounds, including tocopherols and tocotrienols. Studies of the last decade provide strong support for a specific role of alpha-tocopherol in cell signalling and the regulation of gene expression. It produces significant effects on inflammation, cell proliferation and apoptosis that are not shared by other vitamin E isomers with similar antioxidant properties. The different behaviours of vitamin E isomers might relate, at least in part, to the specific effects they exert at the plasma membrane. alpha-Tocopherol is not randomly distributed throughout the phospholipid bilayer of biological membranes, and as compared with other isomers, it shows a propensity to associate with lipid rafts. Distinct aspects of vitamin E transport and metabolism is discussed with emphasis on the interaction between alpha-tocopherol and lipid rafts and the consequences of these interactions on cell metabolism.

alpha-Tocopheryl phosphate--an active lipid mediator?

The vitamin E (alpha-tocopherol, alphaT) derivative, alpha-tocopheryl phosphate (alphaTP), is detectable in small amounts in plasma, tissues, and cultured cells. Studies done in vitro and in vivo suggest that alphaT can become phosphorylated and alphaTP dephosphorylated, suggesting the existence of enzyme(s) with alphaT kinase or alphaTP phosphatase activity, respectively. As a supplement in animal studies, alphaTP can reach plasma concentrations similar to alphaT and only a part is dephosphorylated; thus, alphaTP may act both as pro-vitamin E, but also as phosphorylated form of vitamin E with possibly novel regulatory activities. Many effects of alphaTP have been described: in the test tube alphaTP modulates the activity of several enzymes; in cell culture alphaTP affects proliferation, apoptosis, signal transduction, and gene expression; in animal studies alphaTP prevents atherosclerosis, ischemia/reperfusion injury, and induces hippocampal long-term potentiation. At the molecular level, alphaTP may act as a cofactor for enzymes, as an active lipid mediator similar to other phosphorylated lipids, or indirectly by altering membrane characteristics such as lipid rafts, fluidity, and curvature. In this review, the molecular and cellular activities of alphaTP are examined and the possible functions of alphaTP as a natural compound, cofactor and active lipid mediator involved in signal transduction and gene expression discussed.

The CRAL/TRIO and GOLD domain protein TAP-1 regulates RAF-1 activation

The activation of the protein kinase Raf at the cell membrane is a critical step in cell signaling during development, but the mechanisms that regulate Raf activity remain incompletely defined. We previously demonstrated that the C. elegans cgr-1 gene encodes a CRAL/TRIO domain-containing protein that is a critical modulator of Ras-dependent cell fate specification during C. elegans development. Here we identify the mammalian alpha-tocopherol associated protein-1 (TAP-1) as a functional ortholog of cgr-1. TAP-1 mRNA was expressed in many tissues, and TAP-1 protein colocalized with Ras and Raf at the cell membrane. Reducing TAP-1 expression by RNA interference increased Ras/ERK signaling in multiple cell types. These functional studies demonstrate that CRAL/TRIO domain proteins play a conserved role in regulating Ras signaling. Biochemical analyses indicated that TAP-1 operates at the level of Raf, since TAP-1 function negatively regulated the amount of Raf-1 recruited to GTP-bound Ras at the cell membrane. TAP-1 plays a significant physiological role in controlling cell division, since reducing TAP-1 expression increased the oncogenic capacity of Ras transformed human cancer cell lines. These studies identify TAP-1 as a critical modulator of Ras-mediated cellular signaling.

Alternative splicing and gene polymorphism of the human TAP3/SEC14L4 gene

Three closely related human SEC14p-like proteins (hTAP1, hTAP2, hTAP3, or SEC14L2, SEC14L3, SEC14L4, respectively) have been described that are related to the Saccharomyces cerevisiae SEC14 protein. These proteins may participate in intracellular lipid transport and influence regulatory lipid-dependent events. Here we report the isolation of an alternatively spliced hTAP3 cDNA and a polymorphism within the coding region of the hTAP3/SEC14L4 gene.

Reduced expression of tocopherol-associated protein (TAP/Sec14L2) in human breast cancer

We show that TAP/Sec14L2 had a high expression in normal/benign breast, prostate, and liver tissues as compared to lung, colon, and kidney. Its expression was downregulated in breast cancer cell lines shown by quantitative-PCR. Further, 57% of 141 human invasive breast carcinomas had no or markedly reduced TAP/Sec14L2 expression by immunohistochemical staining, and the rate increased to 80% in high grade invasive carcinomas (p < .01). This downregulation of TAP/Sec14L2 was also present in ductal carcinoma in situ (DCIS) associated with invasive carcinomas. These findings raise the possibility that TAP/Sec14L2 may serve as a tumor suppressor in breast carcinogenesis.