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HIF overexpression correlates with biallelic loss of fumarate hydratase in renal cancer: novel role of fumarate in regulation of HIF stability.

Individuals with hemizygous germline fumarate hydratase (FH) mutations are predisposed to renal cancer. These tumors predominantly exhibit functional inactivation of the remaining wild-type allele, implicating FH inactivation as a tumor-promoting event. Hypoxia-inducible factors are expressed in many cancers and are increased in clear cell renal carcinomas. Under normoxia, the HIFs are labile due to VHL-dependent proteasomal degradation, but stabilization occurs under hypoxia due to inactivation of HIF prolyl hydroxylase (HPH), which prevents HIF hydroxylation and VHL recognition. We demonstrate that FH inhibition, together with elevated intracellular fumarate, coincides with HIF upregulation. Further, we show that fumarate acts as a competitive inhibitor of HPH. These data delineate a novel fumarate-dependent pathway for regulating HPH activity and HIF protein levels.

Adult↗

[Fumarate hydratase activity of various Escherichia coli strains].

The fumarate hydratase activity of intact cells was determined for 36 strains of Escherichia coli, receiver from the All-Union Collection of Microorganisms, to reveal a producer of L-malic acid. A research was made to find optimal media for cultivating microorganisms possessing the fumarate hydratase activity. Spectrophotometric and chromatographic methods were chosen to detect malic acid in the complete reaction mixture, which are available for kinetic study of the malic acid synthesis from potassium fumarate.

Chromatography, Gel↗

Purification and properties of a thermostable fumarate hydratase from the archaeobacterium Sulfolobus solfataricus.

Fumarate hydratase (EC 4.2.1.2) from the extremely thermophilic archaeobacterium Solfolobus solfataricus has been purified to homogeneity by a rapid purification procedure using affinity chromatography and high-performance size-exclusion chromatography, and the enzyme's physical and biochemical properties have been determined. The native enzyme has a molecular mass of 170 kDa and is composed of identical subunits with a molecular mass of 45 kDa, thus indicating a tetrameric structure similar to fumarases isolated from other organisms. The enzyme was active at temperatures ranging from 40 degrees C to 90 degrees C, with a maximum activity at 85 degrees C. The pH optimum for generation of fumarate was found to be pH 8.0. The enzyme showed high stability to denaturation by heat and organic solvents.

Acids↗

Genetic and functional analyses of FH mutations in multiple cutaneous and uterine leiomyomatosis, hereditary leiomyomatosis and renal cancer, and fumarate hydratase deficiency.

Germline mutations of the fumarate hydratase (FH, fumarase) gene are found in the recessive FH deficiency syndrome and in dominantly inherited susceptibility to multiple cutaneous and uterine leiomyomatosis (MCUL). We have previously reported a number of germline FH mutations from MCUL patients. In this study, we report additional FH mutations in MCUL and FH deficiency patients. Mutations can readily be found in about 75% of MCUL cases and most cases of FH deficiency. Some of the more common FH mutations are probably derived from founding individuals. Protein-truncating FH mutations are functionally null alleles. Disease-associated missense FH changes map to highly conserved residues, mostly in or around the enzyme's active site or activation site; we predict that these mutations severely compromise enzyme function. The mutation spectra in FH deficiency and MCUL are similar, although in the latter mutations tend to occur earlier in the gene and, perhaps, are more likely to result in a truncated or absent protein. We have found that not all mutation-carrier parents of FH deficiency children have a strong predisposition to leiomyomata. We have confirmed that renal carcinoma is sometimes part of MCUL, as part of the variant hereditary leiomyomatosis and renal cancer (HLRCC) syndrome, and have shown that these cancers may have either type II papillary or collecting duct morphology. We have found no association between the type or site of FH mutation and any aspect of the MCUL phenotype. Biochemical assay for reduced FH functional activity in the germline of MCUL patients can indicate carriers of FH mutations with high sensitivity and specificity, and can detect reduced FH activity in some patients without detectable FH mutations. We conclude that MCUL is probably a genetically homogeneous tumour predisposition syndrome, primarily resulting from absent or severely reduced fumarase activity, with currently unknown functional consequences for the smooth muscle or kidney cell.

Amino Acid Metabolism, Inborn Errors↗

Germline fumarate hydratase mutations in families with multiple cutaneous and uterine leiomyomata.

Germline mutations in the fumarate hydratase gene (FH) predispose to multiple cutaneous and uterine leiomyoma syndrome (MCL) and MCL associated with renal cell cancer. MCL is inherited in an autosomal dominant pattern, manifesting as skin leiomyoma and uterine fibroids in affected individuals. Fumarate hydratase, a component of the tricarboxylic acid cycle, acts as a tumor suppressor gene in the development of cutaneous and uterine leiomyoma and renal cell cancer in this syndrome. Here we report the clinical and mutational analysis of five families with MCL, with the identification of five new mutations affecting highly conserved residues of the FH protein. These results provide further evidence for the role of the FH gene in the pathogenesis of MCL.

DNA Mutational Analysis↗

Missense mutations in fumarate hydratase in multiple cutaneous and uterine leiomyomatosis and renal cell cancer.

Heterozygous germline mutations in fumarate hydratase (FH) predispose to the multiple cutaneous and uterine leiomyomatosis syndrome (MCUL), which, when co-existing with renal cancer, is also known as hereditary leiomyomatosis and renal cell cancer. Twenty-seven distinct missense mutations represent 68% of FH mutations reported in MCUL. Here we show that FH missense mutations significantly occurred in fully conserved residues and in residues functioning in the FH A-site, B-site, or subunit-interacting region. Of 24 distinct missense mutations, 13 (54%) occurred in the substrate-binding A-site, 4 (17%) in the substrate-binding B-site, and 7 (29%) in the subunit-interacting region. Clustering of missense mutations suggested the presence of possible mutational hotspots. FH functional assay of lymphoblastoid cell lines from 23 individuals with heterozygous FH missense mutations showed that A-site mutants had significantly less residual activity than B-site mutants, supporting data from Escherichia coli that the A-site is the main catalytic site. Missense FH mutations predisposing to renal cancer had no unusual features, and identical mutations were found in families without renal cancer, suggesting a role for genetic or environmental factors in renal cancer development in MCUL. That all missense FH mutations associating with MCUL/hereditary leiomyomatosis and renal cell cancer showed diminished FH enzymatic activity suggests that the tumor suppressor role of fumarate hydratase may relate to its enzymatic function.

Amino Acid Sequence↗

Fumarate hydratase deficiency in monozygotic twins.

Monozygotic twins with fumarate hydratase deficiency presenting with profound hypotonia and developmental delay are reported. This rare organic aciduria has been previously described in random case reports, although, to our knowledge, these are the first reported monozygotic twins and gene testing revealed a novel mutation in both. During their course, one of the twins also developed acute pancreatitis, which has not been previously described in association with this particular organic aciduria.

Amino Acid Metabolism, Inborn Errors↗

No evidence for epigenetic inactivation of fumarate hydratase in leiomyomas and leiomyosarcomas.

Germline mutations in Fumarate Hydratase (FH) cause the development of leiomyomas and leiomyosarcomas in the syndromes Multiple Cutaneous and Uterine Leiomyomata (MCUL1) and Hereditary Leiomyomatosis and Renal Cell Cancer (HLRCC). There is little evidence, however, that FH mutation plays a role in the development of sporadic leiomyomas or leiomyosarcomas. Such observations do not, however, exclude a role for FH in tumour development outside the context of MCUL1/HLRCC, as it is possible that FH expression could be silenced by epigenetic mechanisms. To explore this possibility we have developed a highly specific antibody to FH and analysed a series of forty-five fresh-frozen uterine leiomyomas and nine leiomyosarcomas for FH expression.

Adult↗

Molecular characterization of potato fumarate hydratase and functional expression in Escherichia coli.

The tricarboxylic acid cycle enzyme fumarase (fumarate hydratase; EC 4.2.1.2) catalyzes the reversible hydration of fumarate to L-malate. We report the molecular cloning of a cDNA (StFum-1) that encodes fumarase from potato (Solanum tuberosum L.). RNA blot analysis demonstrated that StFum-1 is most strongly expressed in flowers, immature leaves, and tubers. The deduced protein contains a typical mitochondrial targeting peptide and has a calculated molecular mass of 50.1 kD (processed form). Potato fumarase complemented a fumarase-deficient Escherichia coli mutation for growth on minimal medium that contains acetate or fumarate as the sole carbon source, indicating that functional plant protein was produced in the bacterium. Antiserum raised against the recombinant plant enzyme recognized a 50-kD protein in wild-type but not in StFum-1 antisense plants, indicating specificity of the immunoreaction. A protein of identical size was also detected in isolated potato tuber mitochondria. Although elevated activity of fumarase was previously reported for guard cells (as compared with mesophyll cells), additional screening and genomic hybridization data reported here do not support the hypothesis that a second fumarase gene is expressed in potato guard cells.

Amino Acid Sequence↗

Presence of two forms of fumarase (fumarate hydratase E.C. 4.2.1.2) in mammalian cells: immunological characterization and genetic analysis in somatic cell hybrids. Confirmation of the assignment of a gene necessary for the enzyme expression to human chromosome 1.

Two major forms of fumarate hydratase have been resolved in extracts prepared from a wide variety of mammalian cells by electrophoresis. Fractionation experiments with human and mouse cells suggest that one form (the slower migrating) is localized in the mitochondria, whereas the other form is predominant in the cytoplasm. Analysis of the segregation of the enzyme forms in human-mouse somatic cell hybrids indicates that a gene(s) necessary for the expression of both forms can be assigned to human chromosome 1(confirmation of a previous assignment by van Someren et al., 1974). Electrophoretic analysis suggests that the two forms may be interrelated. Furthermore, they both exhibit identical reactivity toward anti-fumarate hydratase antiserum. It is suggested that a modification of one form may occur in vivo and that the modification may be important in determining the intracellular localization of the enzyme.

Cell Line↗

L-aspartate ammonia-lyase and fumarate hydratase share extensive sequence homology.

Based on our recent determinations of the nucleotide sequences of the L-aspartate ammonia-lyase genes from Escherichia coli and Pseudomonas fluorescens, primary structures of the two L-aspartate ammonia-lyases and fumarate hydratases from Bacillus subtilis and E. coli (N-terminal partial sequence) were compared by computer analysis. These four enzymes exhibited a significant homology of at least 37%, implying that L-aspartate ammonia-lyase and fumarate hydratase share a common evolutionary origin. To authors' knowledge, this feature appears to be the first example showing that two kinds of enzymes catalyzing different types of reactions, albeit similar, share such a high degree of sequence homology.

Amino Acid Sequence↗

[Kinetics of fumarate hydratase reaction catalyzed by free cells of Escherichia coli].

The kinetics of the fumarate hydratase (fumarase) reaction catalyzed by the cells of E. coli strain 85 at high concentrations of the substrate (potassium fumarate) were studied. An automatic procedure for determination of the reaction product--malonic acid--including the use of commercial malate dehydrogenase from porcine heart was developed. The fumarate activity of bacterial cells was studied at different concentrations of the substrate and at different pH values with intact and disrupted cells of E. coli 85 used as the enzyme source. The rate of the fumarase reaction in the E. coli cells was shown to depend on the diffusion and transport processes of the reagent transfer across the cell wall and the cytoplasmic membrane of bacterial cells. The pH optimum of the reaction in free E. coli cells (8-9) and the rate of malonic acid synthesis from potassium fumarate under optimal conditions, which varies within the concentration range of (6--13) x 10(-5) mkmole per mg of protein depending on the quality of cell, were determined.

Escherichia coli↗

Germline fumarate hydratase mutations in patients with ovarian mucinous cystadenoma.

Germline mutations in the fumarate hydratase (FH) gene were recently shown to predispose to the dominantly inherited syndrome, hereditary leiomyomatosis and renal cell cancer (HLRCC). HLRCC is characterized by benign leiomyomas of the skin and the uterus, renal cell carcinoma, and uterine leiomyosarcoma. The aim of this study was to identify new families with FH mutations, and to further examine the tumor spectrum associated with FH mutations. FH germline mutations were screened from 89 patients with RCC, skin leiomyomas or ovarian tumors. Subsequently, 13 ovarian and 48 bladder carcinomas were analyzed for somatic FH mutations. Two patients diagnosed with ovarian mucinous cystadenoma (two out of 33, 6%) were found to be FH germline mutation carriers. One of the changes was a novel mutation (Ala231Thr) and the other one (435insAAA) was previously described in FH deficiency families. These results suggest that benign ovarian tumors may be associated with HLRCC.

Carcinoma, Renal Cell↗

Variability of clinical presentation in fumarate hydratase deficiency.

A 5-year-old girl with a previous diagnosis of cerebral palsy, nonprogressive psychomotor retardation, and hypotonia was found to excrete excessive fumaric acid in urine. Fumarate hydratase activity in skin fibroblasts was 10% of the control value. This case underscores the clinical heterogeneity of neurometabolic disorders and the importance of organic acid analysis in the diagnosis of static encephalopathy.

Cerebral Palsy↗

Involvement of fumarate hydratase in nonsyndromic uterine leiomyomas: genetic linkage analysis and FISH studies.

Recently, germline mutations of the fumarate hydratase (FH) gene, in 1q42.1, have been found to be involved in syndromes associated with uterine leiomyomas (ULs). Compelling evidence also supports a genetic liability to develop nonsyndromic UL, although susceptibility genes have not been reported to date. Loss of heterozygosity (LOH) studies have found no or rare evidence of LOH of FH in nonsyndromic UL. However, the karyotypes of these tumors were not reported, and cytogenetic aberrations of 1q42-44 have been observed infrequently in UL. To determine whether FH mutations also may predispose women to developing nonsyndromic UL, we performed a genetic linkage study with DNA from 123 families containing at least one affected sister pair. In addition, to assess the frequency of FH loss specifically in UL with 1q rearrangements, we performed a fluorescence in situ hybridization (FISH) analysis of UL with 1q rearrangements. Analysis of the genotyping data revealed evidence suggestive of linkage to the FH region among study participants who were less than 40 years of age at diagnosis (Zlr 1.7 at D1S547, P = 0.04). FISH results showed that one copy of FH was absent in 9 of 11 ULs. These data indicate that loss of FH might be a significant event in the pathogenesis of a subset of nonsyndromic ULs.

Adult↗