Epigenetic regulation of the binding activity of translation inhibitory proteins that bind the 3' untranslated region of beta-F1-ATPase mRNA by adenine nucleotides and the redox state

Rs1982809 is a functional biomarker for the prognosis of severe post-traumatic sepsis and MODs

BTLA is a useful biomarker to characterize the immune states of sepsis patients. We investigated the association between genetic variations of BTLA and morbidity of sepsis and MODS in severe traumatic patient. Three tag single nucleotide polymorphisms of BTLA were genotyped in 562 severe trauma patients. To further elucidate the mechanism, mRNA stability, BTLA 3ʹ-UTR activity, and its expression on T lymphocytes were measured. Only rs1982809 which located in 3ʹ-UTR of BTLA showed a significant clinical relevance with the incidence rate of sepsis and MOD scores. The sepsis incidence and MOD score of rs1982809 CC genotype carriers were higher than TT carriers. The percentage of circulating BTLA + CD4 + CD3 +  T lymphocytes was markedly lower in CC genotype carriers. Luciferase activity in plasmids containing C allele was lower than that of T allele. Thus, the differential expression of BTLA on T lymphocytes might be caused by the different 3ʹ-UTR activity induced by rs1982809 T/C. Therefore, rs1982809 is a useful clinical biomarker in the prognosis evaluating of sepsis and subsequent MODS. Moreover, it is also a functional single nucleotide polymorphism affecting the activity of BTLA 3ʹ-UTR and the expression of BTLA in peripheral blood T lymphocytes.

Impact statement

This work is useful in the field of genetic mechanism of severe post-traumatic complications, as it provides important evidence for the influence of BTLA gene polymorphism on sepsis and MODS susceptibility. The results are useful and of importance because rs1982809 is a useful clinical biomarker in the prognosis evaluating of sepsis and subsequent MODS. It is also a functional single nucleotide polymorphism affecting the activity of BTLA 3ʹ-UTR and the expression of BTLA in peripheral blood T lymphocytes.

AMPK and GCN2-ATF4 signal the repression of mitochondria in colon cancer cells

Reprogramming of energetic metabolism is a phenotypic trait of cancer in which mitochondrial dysfunction represents a key event in tumour progression. In the present study, we show that the acquisition of the tumour-promoting phenotype in colon cancer HCT116 cells treated with oligomycin to inhibit ATP synthase is exerted by repression of the synthesis of nuclear-encoded mitochondrial proteins in a process that is regulated at the level of translation. Remarkably, the synthesis of glycolytic proteins is not affected in this situation. Changes in translational control of mitochondrial proteins are signalled by the activation of AMPK (AMP-activated protein kinase) and the GCN2 (general control non-derepressible 2) kinase, leading also to the activation of autophagy. Changes in the bioenergetic function of mitochondria are mimicked by the activation of AMPK and the silencing of ATF4 (activating transcription factor 4). These findings emphasize the relevance of translational control for normal mitochondrial function and for the progression of cancer. Moreover, they demonstrate that glycolysis and oxidative phosphorylation are controlled at different levels of gene expression, offering the cell a mechanistic safeguard strategy for metabolic adaptation under stressful conditions.

Clinical relevance of single nucleotide polymorphisms of the high mobility group box 1 protein gene in patients with major trauma in southwest China

BACKGROUND

High-mobility group box protein 1 (HMGB1) is a pivotal late mediator involved in the development of sepsis and multiple organ dysfunction syndrome (MODS) in critically ill patients. While several single nucleotide polymorphisms (SNPs) have been demonstrated to be critical determinants for outcome of critically ill patients, little is known about the clinical relevance of SNPs of the HMGB1 gene up to date.

METHODS

A total of 3 tag SNPs of the HMGB1 gene were selected using HapMap database and linkage disequilibrium analysis. The tag SNPs were genotyped using a pyrosequencing methodology in 556 unrelated patients with major trauma. Peripheral whole blood samples obtained immediately after admission were determined for HMGB1 production in response to ex vivo lipopolysaccharide (LPS) stimulation.

RESULTS

The rs2249825 SNP and the haplotype TCG were significantly associated with LPS-induced HMGB1 production by peripheral blood leukocytes. There were also significant differences in sepsis morbidity rate and MOD scores among patients with different genotypes of the rs2249825. In addition, the patients with the wild-type haplotype TCG had a lesser sepsis morbidity rate and MOD scores than those without the TCG haplotype.

CONCLUSION

A total of 3 SNPs might act as tag SNPs for the entire HMGB1 gene. The rs2249825 and the haplotype TCG might be used as relevant risk estimate for the development of sepsis and MODS in patients with major trauma.

Genetic association of TLR4/11367 polymorphism with late-onset Alzheimer's disease in a Han Chinese population

The amyloid beta-protein (A-β) deposits in the brains of patients with Alzheimer's disease (AD) are closely associated with innate immune responses that were assumed to play a pivotal role in the pathogenesis of AD. Toll-like receptor 4 (TLR4) is thought to contribute to Aβ clearance. Studies have reported the presence and functional significance of the TLR4/11367 polymorphism in a Han Chinese population. To evaluate the involvement of the TLR4/11367 polymorphism in the risk of late-onset Alzheimer's disease (LOAD), we performed a case-control study to analyze the genotype and allele distributions of the TLR4/11367 polymorphism in a Han Chinese population (137 LOAD cases and 137 healthy controls). There were significant differences in genotype and allele frequencies between LOAD cases and controls (genotype P<0.001, allele P<0.001). After stratification by APOE ε4-carrying status, the C allele of the TLR4/11367 polymorphism was still significantly associated with LOAD in APOE ε4 non-carriers (OR=5.77, 95% CI=3.03-11.00, P<0.001) and carriers (OR=2.03, 95% CI=1.03-3.98, P=0.04). In addition, a logistic regression analysis also conferred positive association between TLR4/11367C and LOAD (dominant model: ORa=3.08, 95% CI=1.60-5.93, P=0.001; recessive model: ORa=8.79, 95% CI=3.31-23.36, P<0.001; additive model: ORa=2.75, 95% CI=1.73-4.37, P<0.001) after adjustment for age, gender, and the APOE ε4 carrier status. This study gives the first evidence that the TLR4/11367 polymorphism was associated with LOAD in a Han Chinese population.

Post-transcriptional regulation of the mitochondrial H(+)-ATP synthase: a key regulator of the metabolic phenotype in cancer

A distinctive metabolic trait of tumors is their enforced aerobic glycolysis. This phenotype was first reported by Otto Warburg, who suggested that the increased glucose consumption of cancer cells under aerobic conditions might result from an impaired bioenergetic activity of their mitochondria. A central player in defining the bioenergetic activity of the cell is the mitochondrial H(+)-ATP synthase. The expression of its catalytic subunit β-F1-ATPase is tightly regulated at post-transcriptional levels during mammalian development and in the cell cycle. Moreover, the down-regulation of β-F1-ATPase is a hallmark of most human carcinomas. In this review we summarize our present understanding of the molecular mechanisms that participate in promoting the "abnormal" aerobic glycolysis of prevalent human carcinomas. The role of the ATPase Inhibitor Factor 1 (IF1) and of Ras-GAP SH3 binding protein 1 (G3BP1), controlling the activity of the H(+)-ATP synthase and the translation of β-F1-ATPase mRNA respectively in cancer cells is emphasized. Furthermore, we underline the role of mitochondrial dysfunction as a pivotal player of tumorigenesis.

Redox control in mammalian embryo development

The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.

HuR and the bioenergetic signature of breast cancer: a low tumor expression of the RNA-binding protein predicts a higher risk of disease recurrence

Downregulation of the catalytic subunit of the mitochondrial H(+)-ATP synthase (beta-F1-ATPase) is a hallmark of many types of cancer. The expression of beta-F1-ATPase is stringently controlled by posttranscriptional mechanisms. Herein, we pursue the identification of beta-F1-ATPase messenger RNA-binding proteins (beta-mRNABPs) that interact and could define the bioenergetic phenotype of the cancer cell in order to establish its relevance as markers of breast cancer progression. RNA immunoprecipitation and RNA affinity chromatography identify HuR as a beta-mRNABP that interacts with the 3'-untranslated region of the transcript. Subcellular fractionation and high-resolution immunoelectron microscopy revealed the cofractionation and presence of HuR in subcellular structures associated to liver mitochondria. Analysis of the expression level of HuR in a cohort of breast carcinomas shows its association with the degree of alteration of the bioenergetic phenotype of the tumor. Moreover, HuR expression is shown to be an independent marker of breast cancer prognosis. A low tumor expression of HuR predicts a higher risk of disease recurrence in early stage breast cancer patients as assessed by clinical and bioenergetic markers of prognosis, strongly supporting the incorporation of HuR as an additional marker for the follow-up of these patients. Mechanistically, overexpression experiments and short hairpin RNA-mediated silencing of HuR in human embryonic kidney and HeLa cells indicate that HuR is not regulating beta-F1-ATPase expression. Overall, the participation of additional RNA-binding proteins in controlling beta-F1-ATPase expression and therefore in defining the bioenergetic signature of the cancer cell is expected.

Mitochondrial ATP synthase disorders: molecular mechanisms and the quest for curative therapeutic approaches

In mammals, the majority of cellular ATP is produced by the mitochondrial F1F(O)-ATP synthase through an elaborate catalytic mechanism. While most subunits of this enzymatic complex are encoded by the nuclear genome, a few essential components are encoded in the mitochondrial genome. The biogenesis of this multi-subunit enzyme is a sophisticated multi-step process that is regulated on levels of transcription, translation and assembly. Defects that result in diminished abundance or functional impairment of the F1F(O)-ATP synthase can cause a variety of severe neuromuscular disorders. Underlying mutations have been identified in both the nuclear and the mitochondrial DNA. The pathogenic mechanisms are only partially understood. Currently, the therapeutic options are extremely limited. Alternative methods of treatment have however been proposed, but still encounter several technical difficulties. The application of novel scientific approaches promises to deepen our understanding of the molecular mechanisms of the ATP synthase, unravel novel therapeutic pathways and improve the unfortunate situation of the patients suffering from such diseases.

Functional significance of the TLR4/11367 polymorphism identified in Chinese Han population

Toll-like receptor 4 (TLR4) is the central signaling receptor for lipopolysaccharide (LPS) in mammals. This study was designed to investigate the functional significance of the G11367C polymorphism, which is a novel variant we identified in the 3' untranslated region of TLR4 gene in Chinese Han population. Three hundred seventy healthy volunteers were selected. The TLR4/11367 polymorphism was genotyped using single-tube bidirectional allele-specific amplification method. The TLR4 protein expression on peripheral leukocytes and plasma tumor necrosis factor alpha levels were determined by means of flow cytometry and enzyme-linked immunosorbent assay. The post-transcriptional effect of the 11367 polymorphism was evaluated by means of reporter gene assay and real-time quantitative polymerase chain reaction. The G11367C polymorphism is a common allele in Chinese Han population, with minor allele frequency of 14.7%. In response to ex vivo LPS stimulation, the TLR4 expression on the surface of peripheral leukocytes and the plasma tumor necrosis factor alpha levels were significantly lower in carriers of 11367C variant allele than in carriers of 11367G allele. This association was allele dose dependent. We also found that the activity and the mRNA expression of luciferase was significantly smaller in human embryonic kidney 293 cells transfected with construct containing 11367C allele than in those transfected with construct containing 11367G allele. Together, these results suggest that the TLR4/11367 polymorphism may be a functional single nucleotide polymorphism, which could attenuate the LPS-induced transmembrane signaling through the alteration of post-transcriptional regulation of 3' untranslated region and target gene expression.

Alteration of expression levels of the oxidative phosphorylation system (OXPHOS) in breast cancer cell mitochondria

Mitochondria are dynamic intracellular organelles playing a central role in cell metabolism by generating ATP, through the oxidative phosphorylation system (OXPHOS). Altered mitochondrial functions have been identified as causative or contributing factors in some degenerative diseases and are becoming crucial to understanding cancer mechanisms. We report on distinct expression differences between mitochondria of normal and breast-infiltrating ductal carcinoma (IDC) cells. Mitochondria isolated from HMC (human mammary carcinoma) and HMEC (human mammary epithelial cell) cultures were assayed for expression levels of the multi-protein OXPHOS complexes using Western blot and densitometric analyses. Depressed expression levels were detected for all HMC OXPHOS complexes. Drastic signal reduction was observed for the succinate-dehydrogenase complex II iron-sulphur protein SDH-B (3.38%), while decreasing was reported for the NADH-ubiquinone oxidoreductase complex I Fe-S protein 3 NDUFS3 (32.78%) and the ubiquinol-cytochrome c reductase complex III protein 2 UQCRC2 (50.34%). A significant signal dropping was detected for the ATP-synthase complex V F(1)beta subunit (18.07%). For the cytochrome-oxidase complex IV (CO), near-depletion of the mitochondrial-encoded COI (4.37%) and no apparent variation of the COIV (97.26%) subunits were observed. CO and ATP-synthase were also assayed by cryo-immunoelectron microscopy (CIEM) on unfractionated HMC and HEMC cell mitochondria. COI and F(1)beta differential expression, invariance of COIV levels were corroborated, while HMC mitochondria morphology deterioration was highlighted. MitoTracker Red and fluorescence immunolabelling merging confirmed CIEM data. MitoTracker Red and Green co-staining showed mitochondria membrane property modulation. These data describe bioenergetic and phenotypic alterations of IDC cell mitochondria, possibly providing new cancer hallmarks.

A message emerging from development: the repression of mitochondrial β-F1-ATPase expression in cancer

Mitochondrial research has experienced a considerable boost during the last decade because organelle malfunctioning is in the genesis and/or progression of a vast array of human pathologies including cancer. The renaissance of mitochondria in the cancer field has been promoted by two main facts: (1) the molecular and functional integration of mitochondrial bioenergetics with the execution of cell death and (2) the implementation of (18)FDG-PET for imaging and staging of tumors in clinical practice. The latter, represents the bed-side translational development of the metabolic hallmark that describes the bioenergetic phenotype of most cancer cells as originally predicted at the beginning of previous century by Otto Warburg. In this minireview we will briefly summarize how the study of energy metabolism during liver development forced our encounter with Warburg's postulates and prompted us to study the mechanisms that regulate the biogenesis of mitochondria in the cancer cell.

The RNA-binding protein PTB exerts translational control on 3'-untranslated region of the mRNA for the ATP synthase beta-subunit

We have recently reported that RNA-binding proteins TIA-1 (T-cell intracellular antigen-1), TIAR (TIA-1 related protein), and HuR (Hu antigen R) modulate the expression of the ATP synthase beta-subunit mRNA (beta-F1-ATPase mRNA) [J.M. Izquierdo, Control of the ATP synthase beta subunit expression by RNA-binding proteins TIA-1, TIAR, and HuR, Biochem. Biophys. Res. Commun. 348 (2006) 703-711]. Here we found that PTB (Polypyrimidine Tract-Binding Protein) is a novel member of the ribonucleoprotein complex that interacts with the beta-F1-ATPase mRNA through an adenosine/uridine (AU)-rich element located to the beta-F1-ATPase 3'-untranslated region (beta-3'-UTR). Co-expression of GFP from a reporter mRNA quimera containing human beta-3'-UTR and recombinant PTB in HeLa cells increased the amount of GFP protein. Interestingly, this effect is not due to increased steady-state levels of GFP-beta-3'-UTR mRNA. Taken together, these results suggest that PTB regulates post-transcriptional expression of the beta-F1-ATPase mRNA at the translational level.

Biogenesis and dynamics of mitochondria during the cell cycle: significance of 3'UTRs

Nowadays, we are facing a renaissance of mitochondria in cancer biology. However, our knowledge of the basic cell biology and on the timing and mechanisms that control the biosynthesis of mitochondrial constituents during progression through the cell cycle of mammalian cells remain largely unknown. Herein, we document the in vivo changes on mitochondrial morphology and dynamics that accompany cellular mitosis, and illustrate the following key points of the biogenesis of mitochondria during progression of liver cells through the cycle: (i) the replication of nuclear and mitochondrial genomes is synchronized during cellular proliferation, (ii) the accretion of OXPHOS proteins is asynchronously regulated during proliferation being the synthesis of beta-F1-ATPase and Hsp60 carried out also at G2/M and, (iii) the biosynthesis of cardiolipin is achieved during the S phase, although full development of the mitochondrial membrane potential (DeltaPsim) is attained at G2/M. Furthermore, we demonstrate using reporter constructs that the mechanism regulating the accretion of beta-F1-ATPase during cellular proliferation is controlled at the level of mRNA translation by the 3'UTR of the transcript. The 3'UTR-driven synthesis of the protein at G2/M is essential for conferring to the daughter cells the original phenotype of the parental cell. Our findings suggest that alterations on this process may promote deregulated beta-F1-ATPase expression in human cancer.

Control of the ATP synthase β subunit expression by RNA-binding proteins TIA-1, TIAR, and HuR

The beta-subunit of the mitochondrial H+-ATP synthase (beta-F1-ATPase) catalyzes the rate-limiting step of ATP formation in eukaryotic cells. Here, we examined the post-transcriptional regulation of human beta-F1-ATPase mediated by the 3'-untranslated region of the mRNA (beta-3'-UTR). Biochemical analysis revealed that the adenosine/uridine (AU)-rich element-binding proteins TIA-1 (T-cell intracellular antigen-1), TIAR (TIA-1-related protein), and HuR (Hu antigen R) interact with the beta-F1-ATPase mRNA through an AU-rich sequence located to the 3'-UTR. Mouse embryonic fibroblasts (MEFs) knocked-out for TIA-1 or RNA interference (RNAi)-mediated knockdown of endogenous TIA-1, TIAR, or HuR in HeLa cells resulted in a decrease in beta-F1-ATPase protein expression. The expression of GFP from a chimeric reporter containing human beta-3'-UTR was also abolished in HeLa cells depleted of TIA-1, TIAR, or HuR. MEFs knocked-in for TIA-1 or the overexpression of RNAi-resistant TIA-1, TIAR, or HuR proteins in the RNAi-treated HeLa cells significantly restored the levels of the expression of both endogenous mouse beta-F1-ATPase protein or recombinant GFP.

Breast carcinomas fulfill the Warburg hypothesis and provide metabolic markers of cancer prognosis

The aim of this study was to investigate selected proteomic markers of the metabolic phenotype of breast carcinomas as prognostic markers of cancer progression. For this purpose, a series of 101 breast carcinomas and 13 uninvolved breast samples were examined for quantitative differences in protein expression of mitochondrial and glycolytic markers. The beta-subunit of the mitochondrial H(+)-ATP synthase (beta-F1-ATPase) and heat shock protein 60 (Hsp60), and the glycolytic glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase were identified by immunological techniques. Correlations of the expression level of the protein markers and of the ratios derived from them were established with the clinicopathological information of the tumors and the follow-up data of the patients. The metabolic proteome of breast cancer specimens revealed a pronounced shift towards an enhanced glycolytic phenotype concurrent with a profound alteration on the mitochondrial beta-F1-ATPase/Hsp60 ratio when compared with normal samples. Discriminant analysis using markers of the metabolic signature as predictor variables revealed a classification sensitivity of approximately 97%. Kaplan-Meier survival analysis showed that several of the proteomic variables significantly correlated with overall and disease-free survival of the patients. The expression level of beta-F1-ATPase per se allowed the identification of a subgroup of breast cancer patients with significantly worse prognosis. Multivariate Cox regression analysis indicated that tumor expression of beta-F1-ATPase is a significant marker independent from clinical variables to assess the prognosis of the patients. We conclude that the alteration of the mitochondrial and glycolytic proteomes is a hallmark feature of breast cancer further providing relevant markers to aid in the prognosis of breast cancer patients.