The human transaldolase gene (TALDO1) is located on chromosome 11 at p15.4-p15.5

Clinical-transcriptional prioritization of the circulating proteome in human heart failure

Given expanding studies in epidemiology and disease-oriented human studies offering hundreds of associations between the human "ome" and disease, prioritizing molecules relevant to disease mechanisms among this growing breadth is important. Here, we link the circulating proteome to human heart failure (HF) propensity (via echocardiographic phenotyping and clinical outcomes) across the lifespan, demonstrating key pathways of fibrosis, inflammation, metabolism, and hypertrophy. We observe a broad array of genes encoding proteins linked to HF phenotypes and outcomes in clinical populations dynamically expressed at a transcriptional level in human myocardium during HF and cardiac recovery (several in a cell-specific fashion). Many identified targets do not have wide precedent in large-scale genomic discovery or human studies, highlighting the complementary roles for proteomic and tissue transcriptomic discovery to focus epidemiological targets to those relevant in human myocardium for further interrogation.

mTOR-dependent loss of PON1 secretion and antiphospholipid autoantibody production underlie autoimmunity-mediated cirrhosis in transaldolase deficiency

Transaldolase deficiency predisposes to chronic liver disease progressing from cirrhosis to hepatocellular carcinoma (HCC). Transition from cirrhosis to hepatocarcinogenesis depends on mitochondrial oxidative stress, as controlled by cytosolic aldose metabolism through the pentose phosphate pathway (PPP). Progression to HCC is critically dependent on NADPH depletion and polyol buildup by aldose reductase (AR), while this enzyme protects from carbon trapping in the PPP and growth restriction in TAL deficiency. Although AR inactivation blocked susceptibility to hepatocarcinogenesis, it enhanced growth restriction, carbon trapping in the non-oxidative branch of the PPP and failed to reverse the depletion of glucose 6-phosphate (G6P) and liver cirrhosis. Here, we show that inactivation of the TAL-AR axis results in metabolic stress characterized by reduced mitophagy, enhanced overall autophagy, activation of the mechanistic target of rapamycin (mTOR), diminished glycosylation and secretion of paraoxonase 1 (PON1), production of antiphospholipid autoantibodies (aPL), loss of CD161+ NK cells, and expansion of CD38+ Ito cells, which are responsive to treatment with rapamycin in vivo. The present study thus identifies glycosylation and secretion of PON1 and aPL production as mTOR-dependent regulatory checkpoints of autoimmunity underlying liver cirrhosis in TAL deficiency.

Transaldolase haploinsufficiency in subjects with acetaminophen-induced liver failure

Transaldolase (TAL) is an enzyme in the pentose phosphate pathway (PPP) that generates NADPH for protection against oxidative stress. While deficiency of other PPP enzymes, such as transketolase (TKT), are incompatible with mammalian cell survival, mice lacking TAL are viable and develop progressive liver disease attributed to oxidative stress. Mice with homozygous or heterozygous TAL deficiency are predisposed to cirrhosis, hepatocellular carcinoma (HCC) and acetaminophen (APAP)-induced liver failure. Both mice and humans with complete TAL deficiency accumulate sedoheptulose 7-phosphate (S7P). Previous human studies relied on screening patients with S7P accumulation, thus excluding potentially pathogenic haploinsufficiency. Of note, mice with TAL haploinsufficiency are also predisposed to HCC and APAP-induced liver failure which are preventable with oral N-acetylcysteine (NAC) administration. Based on TALDO1 DNA sequencing, we detected functional TAL deficiency due to novel, heterozygous variations in two of 94 healthy adults and four of 27 subjects with APAP-induced liver failure (P = .022). The functional consequences of these variations were individually validated by site-directed mutagenesis of normal cDNA and loss of activity by recombinant enzyme. All four patients with TAL haplo-insufficiency with APAP-induced liver failure were successfully treated with NAC. We also document two novel variations in two of 15 children with previously unexplained liver cirrhosis. Examination of the National Center for Biotechnology Information databases revealed 274 coding region variations have been documented in 1125 TALDO1 sequences relative to 25 variations in 2870 TKT sequences (P < .0001). These findings suggest an unexpected prevalence and variety of genetic changes in human TALDO1 with relevance for liver injury that may be preventable by treatment with NAC.

Endogenous retroviral pathogenesis in lupus

PURPOSE OF REVIEW

Genetic and environmental factors influence the development of systemic lupus erythematosus (SLE). Endogenous retroviruses (ERVs) are proposed as a molecular link between the human genome and environmental factors, such as viruses, in lupus pathogenesis.

RECENT FINDINGS

The HRES-1 human ERV encodes a 28-kD nuclear autoantigen and a 24-kD small GTP-ase, termed HRES-1/Rab4. HRES-1/p28 is a target of cross-reactive antiviral antibodies, whereas HRES-1/Rab4 regulates the surface expression of CD4 via endosome recycling. The tat gene of HIV-1 induces the expression of HRES-1/Rab4, which in turn downregulates expression of CD4 and susceptibility to reinfection by HIV-1. HRES-1/Rab4 is overexpressed in lupus T cells where it correlates with increased recycling of CD4 and CD3 and contributes to downregulation of CD3/TCRzeta via lysosomal degradation. Chilblain lupus has been linked to the deficiency of 3'-5' repair exonuclease Trex1 that metabolizes DNA reverse-transcribed from ERV. Trex1 deficiency or blocked integration of ERV-encoded DNA also promotes lupus in murine models.

SUMMARY

ERV proteins may trigger lupus through structural and functional molecular mimicry, whereas the accumulation of ERV-derived nucleic acids stimulates interferon and anti-DNA antibody production in SLE.

Coordinate control of expression of Nrf2-modulated genes in the human small airway epithelium is highly responsive to cigarette smoking

Nuclear factor erythroid 2-related factor 2 (Nrf2) is an oxidant-responsive transcription factor known to induce detoxifying and antioxidant genes. Cigarette smoke, with its large oxidant content, is a major stress on the cells of small airway epithelium, which are vulnerable to oxidant damage. We assessed the role of cigarette smoke in activation of Nrf2 in the human small airway epithelium in vivo. Fiberoptic bronchoscopy was used to sample the small airway epithelium in healthy-nonsmoker and healthy-smoker, and gene expression was assessed using microarrays. Relative to nonsmokers, Nrf2 protein in the small airway epithelium of smokers was activated and localized in the nucleus. The human homologs of 201 known murine Nrf2-modulated genes were identified, and 13 highly smoking-responsive Nrf2-modulated genes were identified. Construction of an Nrf2 index to assess the expression levels of these 13 genes in the airway epithelium of smokers showed coordinate control, an observation confirmed by quantitative PCR. This coordinate level of expression of the 13 Nrf2-modulated genes was independent of smoking history or demographic parameters. The Nrf2 index was used to identify two novel Nrf2-modulated, smoking-responsive genes, pirin (PIR) and UDP glucuronosyltransferase 1-family polypeptide A4 (UGT1A4). Both genes were demonstrated to contain functional antioxidant response elements in the promoter region. These observations suggest that Nrf2 plays an important role in regulating cellular defenses against smoking in the highly vulnerable small airway epithelium cells, and that there is variability within the human population in the Nrf2 responsiveness to oxidant burden.

Genetic variation in Transaldolase 1 and risk of squamous cell carcinoma of the head and neck

BACKGROUND

The Pentose Phosphate Pathway (PPP) is involved in the body's protection against oxidative stress and resistance/susceptibility to apoptosis and thus has been implicated in tumor development and progression. Here we present data examining the association of genetic variation in one of the key enzymes of the PPP, Transaldolase 1 (TALDO1) with squamous cell carcinoma of the head and neck (SCCHN).

METHODS

We performed sequencing analysis to identify common genetic variations in TALDO1 and then investigated their association with SCCHN using samples from a population-based case/control study with both European American (EA) and African American (AA) former and current smokers.

RESULTS

We identified three polymorphisms in TALDO1 that were associated with SCCHN risk in our EA study population. Specifically the 5' upstream variant -490C>G or T (rs10794338), which we identified as tri-allelic, showed a reduced risk compared with any presence of the common allele, odds ratio (OR) [95% confidence interval (95% CI)]: 0.57 (0.38-0.86). Additionally two intronic high frequency polymorphisms demonstrated a positive association with disease, with the presence of the variant IVS1+1874T>A (rs3901233), 1.76 (1.19-2.61) and IVS4+2187A>C (rs4963163), 1.71 (1.16-2.53).

CONCLUSION

These results provide preliminary evidence that genetic polymorphisms in TALDO1 are associated with SCCHN.

Molecular mimicry and immunomodulation by the HRES-1 endogenous retrovirus in SLE

Genetic and environmental factors are believed to influence development of systemic lupus erythematosus (SLE). Endogenous retroviruses (ERV) correspond to the integrated proviral form of infectious retroviruses, which are trapped within the genome due to mutations. ERV represent a key molecular link between the host genome and infectious viral particles. ERV-encoded proteins are recognized by antiviral immune responses and become targets of autoreactivity. Alternatively, ERV protein may influence cellular processes and the life cycle of infectious viruses. As examples, the HRES-1 human ERV encodes a 28-kDa nuclear autoantigen and a 24-kDa small GTP-ase, termed HRES-1/Rab4. HRES-1/p28 is a nuclear autoantigen recognized by cross-reactive antiviral antibodies, while HRES-1/Rab4 regulates surface expression of CD4 and the transferrin receptor (TFR) through endosome recycling. Expression of HRES-1/Rab4 is induced by the tat gene of HIV-1, which in turn down-regulates expression of CD4 and susceptibility to re-infection by HIV-1. CD4 and the TFR play essential roles in formation of the immunological synapse (IS) during normal T-cell activation by a cognate MHC class II peptide complex. The key intracellular transducer of T-cell activation, Lck, is brought to the IS via binding to CD4. T-cell receptorzeta (TCRzeta) chain binds to the TFR. Abnormal T-cell responses in SLE have been associated with reduced lck and TCRzeta chain levels. HRES-1 is centrally located on chromosome 1 at q42 relative to lupus-linked microsatellite markers and polymorphic HRES-1 alleles have been linked to the development of SLE. 1q42 is one of the three most common fragile sites in the human genome, and is inducible by DNA demethylation, a known mechanism of retroviral gene activation. Molecular mimicry and immunomodulation by a ERV, such as HRES-1, may contribute to self-reactivity and abnormal T and B-cell functions in SLE.

ZNF143 mediates basal and tissue-specific expression of human transaldolase

Transaldolase regulates redox-dependent apoptosis through controlling NADPH and ribose 5-phosphate production via the pentose phosphate pathway. The minimal promoter sufficient to drive chloramphenicol acetyltransferase reporter gene activity was mapped to nucleotides -49 to -1 relative to the transcription start site of the human transaldolase gene. DNase I footprinting with nuclear extracts of transaldolase-expressing cell lines unveiled protection of nucleotides -29 to -16. Electrophoretic mobility shift assays identified a single dominant DNA-protein complex that was abolished by consensus sequence for transcription factor ZNF143/76 or mutation of the ZNF76/143 motif within the transaldolase promoter. Mutation of an AP-2alpha recognition sequence, partially overlapping the ZNF143 motif, increased TAL-H promoter activity in HeLa cells, without significant impact on HepG2 cells, which do not express AP-2alpha. Cooperativity of ZNF143 with AP-2alpha was supported by supershift analysis of HeLa cells where AP-2 may act as cell type-specific repressor of TAL promoter activity. However, overexpression of full-length ZNF143, ZNF76, or dominant-negative DNA-binding domain of ZNF143 enhanced, maintained, or abolished transaldolase promoter activity, respectively, in HepG2 and HeLa cells, suggesting that ZNF143 initiates transcription from the transaldolase core promoter. ZNF143 overexpression also increased transaldolase enzyme activity. ZNF143 and transaldolase expression correlated in 21 different human tissues and were coordinately upregulated 14- and 34-fold, respectively, in lactating mammary glands compared with nonlactating ones. Chromatin immunoprecipitation studies confirm that ZNF143/73 associates with the transaldolase promoter in vivo. Thus, ZNF143 plays a key role in basal and tissue-specific expression of transaldolase and regulation of the metabolic network controlling cell survival and differentiation.

Role of endogenous retroviruses in autoimmune diseases

Endogenous retroviruses (ERVs) correspond to the integrated proviral form of infectious retroviruses that are trapped within the genome by mutations. Endogenous retroviruses represent a key molecular link between the host genome and infectious viral particles. Proteins encoded by ERVs are recognized by antiviral immune responses and become targets of autoreactivity. Activation of ERVs, such as human ERV-K or a human T-cell lymphotropic virus-related endogenous sequence, may also mediate pathogenicity of Epstein-Barr virus. Endogenous retrovirus peptides can directly regulate immune responses. Thus, molecular mimicry and immunomodulation by ERVs may account for self-reactivity and abnormal T- and B-cell functions in autoimmune disorders.

Human transaldolase-associated repetitive elements are transcribed by RNA polymerase III

Repetitive elements flanked by exons 2 and 3 of the human transaldolase gene, thus termed transaldolase-associated repetitive elements, TARE, were identified in human DNA. Nonpolyadenylated TARE transcripts were detected by Northern blot analysis and cloned by reverse transcriptase-mediated polymerase chain reaction from human T lymphocytes. A dominant 1085-nucleotide long transcript, TARE-6, contained two adjacent Alu elements, a right monomer and a complete dimer, oriented opposite to the direction of transcription of the transaldolase gene. Reverse transcriptase-polymerase chain reaction and in vitro transcription analyses showed that transcription of TARE-6 proceeded in the orientation of the RNA pol III promoter of the Alu dimer and opposite to the orientation of the TAL-H gene. TAREs lacking RNA polymerase III promoter showed no transcriptional activity. In vitro transcription of TARE-6 was resistant to 1 microg/ml alpha-amanitin but sensitive to 100 microg/ml alpha-amanitin and tagetitoxin, suggesting involvement of RNA polymerase III. TAREs in both the transaldolase and HSAG-1 genomic loci were surrounded by TA target site duplications. Homologies between transaldolase and HSAG-1 break off internally at splice donor and acceptor sites. The results suggest RNA polymerase III-mediated transcription of TARE may be a source of repetitive elements, contributing to distinct genes and thus shaping the human genome.

Human Transaldolase and Cross-Reactive Viral Epitopes Identified by Autoantibodies of Multiple Sclerosis Patients

Multiple sclerosis is mediated by an autoimmune process causing selective destruction of oligodendrocytes. Transaldolase, which is expressed in the brain selectively in oligodendrocytes, is a target of high affinity autoantibodies in serum and cerebrospinal fluid of multiple sclerosis patients. A three-dimensional model of human transaldolase was developed based on the crystal structure of the enzyme from Escherichia coli. To identify immunodominant epitopes, 33 peptides overlapping human transaldolase by 5 amino acids were synthesized. Ab 12484, raised against enzymatically active human transaldolase, recognized antigenic determinants corresponding to linear epitopes (residues 27–31 and 265–290) and α helices (residues 75–98 and 302–329). Four immunodominant peptides harboring charged amino acid residues with topographically exposed side chains were identified by sera from 13 multiple sclerosis patients with predetermined autoreactivity to transaldolase. Autoantibodies binding to the most prominent human transaldolase epitope, between residues 271 and 285, showed cross-reactivity with Epstein-Barr and herpes simplex virus type 1 capsid-derived peptides. Molecular mimicry between immunodominant autoepitopes and viral Ags may be a decisive factor in directing autoimmunity to transaldolase in multiple sclerosis patients.