SUMOylation controls Hu antigen R posttranscriptional activity in liver cancer.

The posttranslational modification of proteins critically influences many biological processes and is a key mechanism that regulates the function of the RNA-binding protein Hu antigen R (HuR), a hub in liver cancer. Here, we show that HuR is SUMOylated in the tumor sections of patients with hepatocellular carcinoma in contrast to the surrounding tissue, as well as in human cell line and mouse models of the disease. SUMOylation of HuR promotes major cancer hallmarks, namely proliferation and invasion, whereas the absence of HuR SUMOylation results in a senescent phenotype with dysfunctional mitochondria and endoplasmic reticulum. Mechanistically, SUMOylation induces a structural rearrangement of the RNA recognition motifs that modulates HuR binding affinity to its target RNAs, further modifying the transcriptomic profile toward hepatic tumor progression. Overall, SUMOylation constitutes a mechanism of HuR regulation that could be potentially exploited as a therapeutic strategy for liver cancer.

A molecular signature for the metabolic syndrome by urine metabolomics.

BACKGROUND: Metabolic syndrome (MetS) is a multimorbid long-term condition without consensual medical definition and a diagnostic based on compatible symptomatology. Here we have investigated the molecular signature of MetS in urine. METHODS: We used NMR-based metabolomics to investigate a European cohort including urine samples from 11,754 individuals (18-75 years old, 41% females), designed to populate all the intermediate conditions in MetS, from subjects without any risk factor up to individuals with developed MetS (4-5%, depending on the definition). A set of quantified metabolites were integrated from the urine spectra to obtain metabolic models (one for each definition), to discriminate between individuals with MetS. RESULTS: MetS progression produces a continuous and monotonic variation of the urine metabolome, characterized by up- or down-regulation of the pertinent metabolites (17 in total, including glucose, lipids, aromatic amino acids, salicyluric acid, maltitol, trimethylamine N-oxide, and p-cresol sulfate) with some of the metabolites associated to MetS for the first time. This metabolic signature, based solely on information extracted from the urine spectrum, adds a molecular dimension to MetS definition and it was used to generate models that can identify subjects with MetS (AUROC values between 0.83 and 0.87). This signature is particularly suitable to add meaning to the conditions that are in the interface between healthy subjects and MetS patients. Aging and non-alcoholic fatty liver disease are also risk factors that may enhance MetS probability, but they do not directly interfere with the metabolic discrimination of the syndrome. CONCLUSIONS: Urine metabolomics, studied by NMR spectroscopy, unravelled a set of metabolites that concomitantly evolve with MetS progression, that were used to derive and validate a molecular definition of MetS and to discriminate the conditions that are in the interface between healthy individuals and the metabolic syndrome.

Therapeutic Targeting of Fumaryl Acetoacetate Hydrolase in Hereditary Tyrosinemia Type I.

Fumarylacetoacetate hydrolase (FAH) is the fifth enzyme in the tyrosine catabolism pathway. A deficiency in human FAH leads to hereditary tyrosinemia type I (HT1), an autosomal recessive disorder that results in the accumulation of toxic metabolites such as succinylacetone, maleylacetoacetate, and fumarylacetoacetate in the liver and kidney, among other tissues. The disease is severe and, when untreated, it can lead to death. A low tyrosine diet combined with the herbicidal nitisinone constitutes the only available therapy, but this treatment is not devoid of secondary effects and long-term complications. In this study, we targeted FAH for the first-time to discover new chemical modulators that act as pharmacological chaperones, directly associating with this enzyme. After screening several thousand compounds and subsequent chemical redesign, we found a set of reversible inhibitors that associate with FAH close to the active site and stabilize the (active) dimeric species, as demonstrated by NMR spectroscopy. Importantly, the inhibitors are also able to partially restore the normal phenotype in a newly developed cellular model of HT1.

Repurposing ciclopirox as a pharmacological chaperone in a model of congenital erythropoietic porphyria.

Congenital erythropoietic porphyria is a rare autosomal recessive disease produced by deficient activity of uroporphyrinogen III synthase, the fourth enzyme in the heme biosynthetic pathway. The disease affects many organs, can be life-threatening, and currently lacks curative treatments. Inherited mutations most commonly reduce the enzyme's stability, altering its homeostasis and ultimately blunting intracellular heme production. This results in uroporphyrin by-product accumulation in the body, aggravating associated pathological symptoms such as skin photosensitivity and disfiguring phototoxic cutaneous lesions. We demonstrated that the synthetic marketed antifungal ciclopirox binds to the enzyme, stabilizing it. Ciclopirox targeted the enzyme at an allosteric site distant from the active center and did not affect the enzyme's catalytic role. The drug restored enzymatic activity in vitro and ex vivo and was able to alleviate most clinical symptoms of congenital erythropoietic porphyria in a genetic mouse model of the disease at subtoxic concentrations. Our findings establish a possible line of therapeutic intervention against congenital erythropoietic porphyria, which is potentially applicable to most of deleterious missense mutations causing this devastating disease.

Bioengineered PBGD variant improves the therapeutic index of gene therapy vectors for acute intermittent porphyria.

A first-in-human gene therapy trial using a recombinant adeno-associated viral (rAAV) vector for acute intermittent porphyria (AIP) reveals that higher doses would be required to reach therapeutic levels of the porphobilinogen deaminase (PBGD) transgene. We developed a hyperfunctional PBGD protein to improve the therapeutic index without increasing vector dose. A consensus protein sequence from 12 mammal species was compared to the human PBGD sequence, and eight amino acids were selected. I291M and N340S variants showed the highest increase in enzymatic activity when expressed in prokaryotic and eukaryotic systems. In silico analysis indicates that isoleucine 291 to methionine and asparagine 340 to serine variants did not affect the active site of the enzyme. In vitro analysis indicated a synergistic interaction between these two substitutions that improve kinetic stability. Finally, full protection against a phenobarbital-induced attack was achieved in AIP mice after the administration of 1 × 1011 gc/kg of rAAV2/8-PBGD-I291M/N340S vector; three times lower than the dose required to achieve full protection with the control rAAV2/8-hPBGD vector. In conclusion, we have developed and characterized a hyperfunctional PBGD protein. The inclusion of this variant sequence in a rAAV2/8 vector allows the effective dose to be lowered in AIP mice.

Missense UROS mutations causing congenital erythropoietic porphyria reduce UROS homeostasis that can be rescued by proteasome inhibition.

Congenital erythropoietic porphyria (CEP) is an inborn error of heme biosynthesis characterized by uroporphyrinogen III synthase (UROS) deficiency resulting in deleterious porphyrin accumulation in blood cells responsible for hemolytic anemia and cutaneous photosensitivity. We analyzed here the molecular basis of UROS impairment associated with twenty nine UROS missense mutations actually described in CEP patients. Using a computational and biophysical joint approach we predicted that most disease-causing mutations would affect UROS folding and stability. Through the analysis of enhanced green fluorescent protein-tagged versions of UROS enzyme we experimentally confirmed these data and showed that thermodynamic instability and premature protein degradation is a major mechanism accounting for the enzymatic deficiency associated with twenty UROS mutants in human cells. Since the intracellular loss in protein homeostasis is in excellent agreement with the in vitro destabilization, we used molecular dynamic simulation to rely structural 3D modification with UROS disability. We found that destabilizing mutations could be clustered within three types of mechanism according to side chain rearrangements or contact alterations within the pathogenic UROS enzyme so that the severity degree correlated with cellular protein instability. Furthermore, proteasome inhibition using bortezomib, a clinically available drug, significantly enhanced proteostasis of each unstable UROS mutant. Finally, we show evidence that abnormal protein homeostasis is a prevalent mechanism responsible for UROS deficiency and that modulators of UROS proteolysis such as proteasome inhibitors or chemical chaperones may represent an attractive therapeutic option to reduce porphyrin accumulation and prevent skin photosensitivity in CEP patients when the genotype includes a missense variant.

Tuning intracellular homeostasis of human uroporphyrinogen III synthase by enzyme engineering at a single hotspot of congenital erythropoietic porphyria.

Congenital erythropoietic porphyria (CEP) results from a deficiency in uroporphyrinogen III synthase enzyme (UROIIIS) activity that ultimately stems from deleterious mutations in the uroS gene. C73 is a hotspot for these mutations and a C73R substitution, which drastically reduces the enzyme activity and stability, is found in almost one-third of all reported CEP cases. Here, we have studied the structural basis, by which mutations in this hotspot lead to UROIIIS destabilization. First, a strong interdependency is observed between the volume of the side chain at position 73 and the folded protein. Moreover, there is a correlation between the in vitro half-life of the mutated proteins and their expression levels in eukaryotic cell lines. Molecular modelling was used to rationalize the results, showing that the mutation site is coupled to the hinge region separating the two domains. Namely, mutations at position 73 modulate the inter-domain closure and ultimately affect protein stability. By incorporating residues capable of interacting with R73 to stabilize the hinge region, catalytic activity was fully restored and a moderate increase in the kinetic stability of the enzyme was observed. These results provide an unprecedented rationale for a destabilizing missense mutation and pave the way for the effective design of molecular chaperones as a therapy against CEP.

Spn1 regulates the GNBP3-dependent Toll signaling pathway in Drosophila melanogaster.

The Drosophila genome encodes 29 serpins, most of unknown function. We show here that Spn1 is an active protease inhibitor of the serpin superfamily. Spn1 inhibits trypsin in vitro and regulates the Toll-mediated immune response in vivo. Expression of the Toll-dependent transcripts Drosomycin and IM1 is increased in Spn1 null mutants. Overexpression of Spn1 reduces the induction of Drosomycin upon immune challenge with fungi but not Gram-positive bacteria. Similar reductions in Drosomycin levels are observed in the psh, spz, and grass mutants of the Toll signaling pathway. These results support a role of Spn1 as a repressor of Toll activation upon fungal infection. Epistatic analysis places Spn1 upstream of Spätzle processing enzyme and Grass, in the fungal cell wall-activated side branch of the pathway. Overexpression of the pattern recognition receptor GNBP3 activates the ß-1,3-glucan-sensitive side branch of the Toll pathway. The resultant increased Drosomycin level is reduced by concomitant overexpression of Spn1, confirming that Spn1 regulates the fungal cell wall side branch. Spn1 null mutants show altered susceptibility to fungal infection compared to the wild type, demonstrating a requirement for Spn1 in the fine regulation of the immune response.

Protease inhibitors and proteolytic signalling cascades in insects.

Proteolytic signalling cascades control a wide range of physiological responses. In order to respond rapidly, protease activity must be maintained at a basal level: the component zymogens must be sequentially activated and actively degraded. At the same time, signalling cascades must respond precisely: high target specificity is required. The insects have a wide range of trapping- and tight-binding protease inhibitors, which can regulate the activity of individual proteases. In addition, the interactions between component proteases of a signalling cascade can be modified by serine protease homologues. The suicide-inhibition mechanism of serpin family inhibitors gives rapid turnover of both protease and inhibitor, but target specificity is inherently broad. Similarly, the TEP/macroglobulins have extremely broad target specificity, which suits them for roles as hormone transport proteins and sensors of pathogenic virulence factors. The tight-binding inhibitors, on the other hand, have a lock-and-key mechanism capable of high target specificity. In addition, proteins containing multiple tight-binding inhibitory domains may act as scaffolds for the assembly of signalling complexes. Proteolytic cascades regulated by combinations of different types of inhibitor could combine the rapidity of suicide-inhibitors with the specificity lock-and-key inhibitors. This would allow precise control of physiological responses and may turn out to be a general rule.

Analysis of FMR1 gene expression in female premutation carriers using robust segmented linear regression models.

Fragile X syndrome is caused by the absence or reduction of the fragile X mental retardation protein (FMRP) because FMR1 gene expression is reduced. Alleles with repeat sizes of 55-200 are classified as premutations, and it has been demonstrated that FMR1 expression is elevated in the premutation range. However, the majority of the studies reported were performed in males. We studied FMR1 expression in 100 female fragile X family members from the northern region of Spain using quantitative (fluorescence) real-time polymerase chain reaction. Of these 100 women, 19 had normal alleles, 19 were full mutation carriers, and 62 were premutation carriers. After confirming differences between the three groups of females, and increased levels of the FMR1 transcript among premutation carriers, we found that the relationship between mRNA levels and repeat size is nonlinear. These results were obtained using a novel methodology that, based on the size of the CGG repeats, allows us to find out the most probable threshold from which the relationship between CGG repeat number and mRNA levels changes. Using this approach, a significant positive correlation between CGG repeats and total mRNA levels has been found in the premutation range <100 CGG, but this correlation diminishes from 100 onward. However, when correcting by the X inactivation ratio, mRNA levels increase as the number of CGG repeats increases, and this increase is highly significant over 100 CGG. We suggest that due to skewed X inactivation, mRNA levels tend to normalize in females when the number of CGG repeats increases.