HIF overexpression correlates with biallelic loss of fumarate hydratase in renal cancer: novel role of fumarate in regulation of HIF stability.
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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. (+info)
Increased risk of cancer in patients with fumarate hydratase germline mutation.
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Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a tumour predisposition syndrome caused by heterozygous germline mutations in the fumarate hydratase (FH) gene. The condition is characterised by predisposition to benign leiomyomas of the skin and the uterus, renal cell carcinoma (RCC), and uterine leiomyosarcoma (ULMS). To comprehensively examine the cancer risk and tumour spectrum in Finnish FH mutation positive families, genealogical and cancer data were obtained from 868 individuals. The cohort analysis of the standardised incidence ratios (SIR) was analysed from 256 individuals. FH mutation status was analysed from all available individuals (n = 98). To study tumour spectrum in FH mutation carriers, loss of the wild type allele was analysed from all available tumours (n = 22). The SIR was 6.5 for RCC and 71 for ULMS. The overall cancer risk was statistically significantly increased in the age group of 15-29 years, consistent with features of cancer predisposition families in general. FH germline mutation was found in 55% of studied individuals. Most RCC and ULMS tumours displayed biallelic inactivation of FH, as did breast and bladder cancers. In addition, several benign tumours including atypical uterine leiomyomas, kidney cysts, and adrenal gland adenomas were observed. The present study confirms with calculated risk ratios the association of early onset RCC and ULMS with FH germline mutations in Finns. Some evidence for association of breast and bladder carcinoma with HLRCC was obtained. The data enlighten the organ specific malignant potential of HLRCC. (+info)
Missense mutations in fumarate hydratase in multiple cutaneous and uterine leiomyomatosis and renal cell cancer.
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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. (+info)
Fumarase C, the stable fumarase of Escherichia coli, is controlled by the soxRS regulon.
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Fumarase C was strongly induced by paraquat in a parental strain of Escherichia coli but was not induced in a strain lacking the soxRS response. Moreover, a strain that constitutively expresses the soxRS regulon contained more fumarase C than did the parental strain. The Mn-containing superoxide dismutase and glucose-6-phosphate dehydrogenase, members of the soxRS regulon, were similarly induced by paraquat. Mutational defects in glucose-6-phosphate dehydrogenase increased the induction of fumarase C by paraquat. For Mn-containing superoxide dismutase, responsiveness to paraquat was also enhanced in the glucose-6-phosphate dehydrogenase-defective strains. Overproduction of the Mn-containing superoxide dismutase, elicited by isopropyl beta-D-thiogalactoside in a tac-sodA fusion strain, did not diminish induction of fumarase C or of glucose-6-phosphate dehydrogenase by paraquat, and induction of these enzymes was more sensitive to paraquat when the cells were growing on succinate rather than on LB medium. These results indicate that fumarase C is a member of the soxRS regulon and that this regulon does not respond to changes in O2- concentration but perhaps does respond to some consequence of a decrease in the ratio of NADPH to NADP+. (+info)
Serum and erythocyte argininosuccinate lyase assay by NADH fluorescence generated from formed fumarate.
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Measurement of argininosuccinase (I; EC 4.3.2.1) activity is useful in following the course of disease in hepatitis and in screening for the genetic defect, argininosuccinic aciduria. Methodology is proposed for a novel procedure for the determination of I in serum and erythrocytes. In the procedure, fumarate, generated in the reaction, is assayed by conversion to malate with fumarase, determining the malate enzymatically with malate dehydrogenase, and estimating the NADH formed spectrofluorometrically. By this procedure, the enzyme activity in serum from normal individuals is less than 11 mumol/liter of erthrocytes/per hour. The correlation coefficient between results by this method and by the colorimetric method, which measures the arginine generated in the reaction, is +0.97 for serum and +0.98 for erythrocytes. The proposed procedure has a relatively low initial blank, requires less serum, and is completed faster. (+info)
Distinct expression profile in fumarate-hydratase-deficient uterine fibroids.
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Defects in mitochondrial enzymes predispose to severe developmental defects as well as tumorigenesis. Heterozygous germline mutations in the nuclear gene encoding fumarate hydratase (FH), an enzyme catalyzing the hydration of fumarate in the Krebs tricarboxylic acid cycle, cause hereditary leiomyomatosis and renal cell cancer; yet the connection between disruption of mitochondrial metabolic pathways and neoplasia remains to be discovered. We have used an expression microarray approach for studying differences in global gene expression pattern caused by mutations in FH. Seven uterine fibroids carrying FH mutations were compared with 15 fibroids with wild-type FH. The two groups showed markedly different expression profiles, and multiple differentially expressed genes were detected. The most significant increase in FH mutants was seen in the expression of carbohydrate metabolism- and glycolysis-related genes. Other significantly up-regulated gene categories in FH mutants were, for example, iron ion homeostasis and oxidoreduction. Genes with lower expression in FH-mutant fibroids belonged to groups such as extracellular matrix, cell adhesion, muscle development and cell contraction. We show that FH mutations alter significantly the expression profiles of fibroids, most strikingly increasing the expression of genes involved in glycolysis. (+info)
Evidence that rat liver mitochondrial and cytosolic fumarases are synthesized from one species of mRNA by alternative translational initiation at two in-phase AUG codons.
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Rat liver contains two isozymes of fumarase, mitochondrial and cytosolic enzymes. Recently, we suggested that the precursors of both isozymes might be synthesized by one species of mRNA [Suzuki, T., Sato, M., Yoshida, T. & Tuboi, S. (1989) J. Biol. Chem. 264, 2581-2586]. To examine this possibility, we have isolated and characterized rat genomic clones for fumarase. The isolated clones covered almost all of the 5' half of the fumarase gene consisting of five exons. The first exon contained the whole 5' non-coding region and the signal peptide of mitochondrial precursor. The second exon encoded 45 amino acid residues of both mature proteins, starting from the N-terminal alanine. By using the boundary region of the first intron and the second exon as an S1-nuclease-analysis probe, we obtained conclusive evidence that rat liver contains no other mRNA specific for the cytosolic isozyme of fumarase. Two transcription-initiation sites were identified by further S1-nuclease-mapping analysis and were shown to be located very close to each other, differing by only four bases in length. Therefore, these sites were considered to be functionally the same. The results obtained by hybrid-selected translation, with a DNA fragment of the 5' non-coding region as a hybridization probe for selecting mRNA, were consistent with the above findings. We found a plausible secondary structure within the 5' non-coding mRNA sequence that may impede initiation and so alter the efficiency of translation. We also discuss the mechanism regulating translational initiation. (+info)
Multiple cutaneous and uterine leiomyomatosis (Reed's syndrome).
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A 51-year-old woman with a history of uterine fibroids status post myomectomy and hysterectomy presented for evaluation and treatment of intermittently painful papules of the left shoulder. Histopathologic examination showed a proliferation of smooth muscle fascicles consistent with the diagnosis of cutaneous leiomyomas. Genetic sequencing demonstrated a novel mutation in the fumarate hydratase gene that confirmed the diagnosis of Reed's syndrome. A subset of individuals with Reed's syndrome is predisposed to develop a papillary renal-cell carcinoma, so appropriate radiologic examinations should be performed. Treatment of the pain caused by cutaneous leiomyomas includes the use of nifedipine, nitroglycerine, phenoxybenzamine, surgical excision, and carbon dioxide laser ablation. (+info)