Uterine Leiomyomas with Specific Histology Features of Two Fumarate Hydratase/Succinate Dehydrogenase-Deficient Tumors: A Double Case Report.

Background and Objectives: Mutations in succinate dehydrogenase (SDH) and fumarate hydratase (FH) give rise to various familial cancer syndromes, with these alterations being characteristic of certain types of histomorphologically specific leiomyomas that hold significant predictive value. Materials and Methods: This study presents two cases of uterine leiomyomas exhibiting rare histomorphological and genetic characteristics, which are crucial for prognosis and further treatment. Results: Distinct histopathological features such as marked nuclear atypia, intracellular eosinophilic globules, and abnormal intratumoral vessels raise suspicion for specific leiomyoma subtypes, which carry predictive significance for additional hereditary cancer syndromes. Immunohistochemical analysis confirmed FH/SDH deficiency in both patients, who underwent careful follow-up. Conclusions: This study describes two cases involving unusual leiomyomas, the histopathological characteristics of which may easily go unrecognized. These features hold predictive significance because their specific mutations point to additional hereditary cancer syndromes, highlighting the need for further examinations.

Germline and Somatic Fumarate Hydratase Testing in Atypical Uterine Leiomyomata.

Women with germline pathogenic variants (PV) in the fumarate hydratase (FH) gene develop cutaneous and uterine leiomyomata and have an increased risk of developing aggressive renal cell carcinomas. Many of these women are unaware of their cancer predisposition until an atypical uterine leiomyoma is diagnosed during a myomectomy or hysterectomy, making a streamlined genetic counseling process after a pathology-based atypical uterine leiomyoma diagnosis critical. However, the prevalence of germline pathogenic/likely PVs in FH among atypical uterine leiomyomata cases is unknown. To better understand FH germline PV prevalence and current patterns of genetic counseling and germline genetic testing, we undertook a retrospective review of atypical uterine leiomyomata cases at a single large center. We compared clinical characteristics between the FH PV, FH wild-type (WT), and unknown genetic testing cohorts. Of the 144 cases with atypical uterine leiomyomata with evaluable clinical data, only 49 (34%) had documented genetic test results, and 12 (8.3%) had a germline FH PV. There were 48 IHC-defined FH-deficient cases, of which 41 (85%) had FH testing and nine had a germline FH PV, representing 22% of the tested cohort and 18.8% of the FH-deficient cohort. Germline FH PVs were present in 8.3% of evaluable patients, representing 24.5% of the cohort that completed genetic testing. These data highlight the disconnect between pathology and genetic counseling, and help to refine risk estimates that can be used when counseling patients with atypical uterine leiomyomata. PREVENTION RELEVANCE: Women diagnosed with fumarate hydratase (FH)-deficient uterine leiomyomata are at increased risk of renal cancer. This work suggests a more standardized pathology-genetic counseling referral pathway for these patients, and that research on underlying causes of FH-deficient uterine leiomyomata in the absence of germline FH pathogenic/likely pathogenic variants is needed.

Segregation, immunohistochemical, molecular and functional analyses classify a novel missense variant in fumarate hydratase (FH) as pathogenic.

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an autosomal dominant cancer predisposition syndrome characterized by cutaneous leiomyomas, uterine leiomyomas, and aggressive renal cancer. Germline variants in the fumarate hydratase (FH) gene predispose to HLRCC. Identifying germline pathogenic FH variants enables lifetime renal cancer screening and genetic testing for family members. In this report, we present a FH missense variant (c.1039T>C (p.S347P)), initially classified as a variant of uncertain significance. Clinical assessment, histopathological findings, molecular genetic studies, and enzymatic activity studies support the re-classification of the FH c.1039T>C variant to "pathogenic" based on ACMG/AMP criteria. Further insights into pathological recognition of FH-deficient renal cancer are discussed and should be recognized. This study has shown how (a) detailed multi-disciplinary analyses of a single variant can reclassify rare missense variants in FH and (b) careful pathological review of renal cancers is obligatory when HLRCC is suspected.

Memory/Active T-Cell Activation Is Associated with Immunotherapeutic Response in Fumarate Hydratase-Deficient Renal Cell Carcinoma.

PURPOSE: Fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) is a rare and lethal subtype of kidney cancer. However, the optimal treatments and molecular correlates of benefits for FH-deficient RCC are currently lacking. EXPERIMENTAL DESIGN: A total of 91 patients with FH-deficient RCC from 15 medical centers between 2009 and 2022 were enrolled in this study. Genomic and bulk RNA-sequencing (RNA-seq) were performed on 88 and 45 untreated FH-deficient RCCs, respectively. Single-cell RNA-seq was performed to identify biomarkers for treatment response. Main outcomes included disease-free survival (DFS) for localized patients, objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) for patients with metastasis. RESULTS: In the localized setting, we found that a cell-cycle progression signature enabled to predict disease progression. In the metastatic setting, first-line immune checkpoint inhibitor plus tyrosine kinase inhibitor (ICI+TKI) combination therapy showed satisfactory safety and was associated with a higher ORR (43.2% vs. 5.6%), apparently superior PFS (median PFS, 17.3 vs. 9.6 months, P = 0.016) and OS (median OS, not reached vs. 25.7 months, P = 0.005) over TKI monotherapy. Bulk and single-cell RNA-seq data revealed an enrichment of memory and effect T cells in responders to ICI plus TKI combination therapy. Furthermore, we identified a signature of memory and effect T cells that was associated with the effectiveness of ICI plus TKI combination therapy. CONCLUSIONS: ICI plus TKI combination therapy may represent a promising treatment option for metastatic FH-deficient RCC. A memory/active T-cell-derived signature is associated with the efficacy of ICI+TKI but necessitates further validation.

Genomic profile analysis of leiomyomas with bizarre nuclei and fumarate hydratase deficient leiomyomas: Strengths, weaknesses, and limitations of array-CGH interpretation.

A close relationship has been demonstrated between genomic complexity and clinical outcome in uterine smooth muscle tumors. We studied the genomic profiles by array-CGH of 28 fumarate hydratase deficient leiomyomas and 37 leiomyomas with bizarre nuclei (LMBN) from 64 patients. Follow-up was available for 46 patients (from three to 249 months, mean 87.3 months). All patients were alive without evidence of disease. For 51 array-CGH interpretable tumors the mean Genomic Index (GI) was 16.4 (median: 9.8; from 1 to 57.8), significantly lower than the mean GI in LMS (mean GI 51.8, p < 0.001). We described three groups: (1) a group with FH deletion (24/58) with low GI (mean GI: 11 vs. 22,4, p = 0.02), (2) a group with TP53 deletion (17/58) with higher GI (22.4 vs. 11 p = 0.02), and (3) a group without genomic events on FH or TP53 genes (17/58) (mean GI:18.3; from 1 to 57.8). Because none of these tumors recurred and none showed morphological features of LMS we concluded that GI at the cut-off of 10 was not applicable in these subtypes of LM. By integration of all those findings, a GI <10 in LMBN remains a valuable argument for benignity. Conversely, in LMBN a GI >10 or alteration in tumor suppressor genes, should not alone warrant a diagnosis of malignancy. Nine tumors were tested with Nanocind CINSARC® signature and all were classified in low risk of recurrence. We propose, based on our observations, a diagnostic approach of these challenging lesions.

Metabolic rewiring enables ammonium assimilation via a non-canonical fumarate-based pathway.

Glutamate serves as the major cellular amino group donor. In Bacillus subtilis, glutamate is synthesized by the combined action of the glutamine synthetase and the glutamate synthase (GOGAT). The glutamate dehydrogenases are devoted to glutamate degradation in vivo. To keep the cellular glutamate concentration high, the genes and the encoded enzymes involved in glutamate biosynthesis and degradation need to be tightly regulated depending on the available carbon and nitrogen sources. Serendipitously, we found that the inactivation of the ansR and citG genes encoding the repressor of the ansAB genes and the fumarase, respectively, enables the GOGAT-deficient B. subtilis mutant to synthesize glutamate via a non-canonical fumarate-based ammonium assimilation pathway. We also show that the de-repression of the ansAB genes is sufficient to restore aspartate prototrophy of an aspB aspartate transaminase mutant. Moreover, in the presence of arginine, B. subtilis mutants lacking fumarase activity show a growth defect that can be relieved by aspB overexpression, by reducing arginine uptake and by decreasing the metabolic flux through the TCA cycle.

Conditional expression of FumA in Aspergillus niger enhances synthesis of L-malic acid.

Currently, the L-malic acid titer achieved through Aspergillus niger fermentation reaches 201 g/L, meeting industrial demands satisfactorily. However, the co-presence of structurally similar fumaric acid and succinic acid in fermentation products suggests a theoretical potential for further improvement in L-malic acid production. In the tricarboxylic acid cycle, fumarate reductase mediates the conversion of succinic acid to fumaric acid. Subsequently, fumarase catalyzes the conversion of fumaric acid to L-malic acid. Notably, both enzymatic reactions are reversible. Our investigation revealed that A. niger contains only one mitochondria-located fumarase FumA. Employing CRISPR-Cas9 technology, we performed a replacement of the fumA promoter with a doxycycline-induced promoter Tet. Under non-inducing condition, the conditional strain exhibited increased levels of fumaric acid and succinic acid. It strongly suggests that FumA mainly promotes the flow of fumaric acid to L-malic acid. Furthermore, a promoter PmfsA that is exclusively activated in a fermentation medium by calcium carbonate was identified through RNA-sequencing screening. Utilizing PmfsA to regulate fumA expression led to a 9.0% increase in L-malic acid titer, an 8.75% increase in yield (glucose to L-malic acid), and an 8.86% enhancement in productivity. This research serves as a significant step toward expediting the industrialization of L-malic acid synthesis via biological fermentation. Additionally, it offers valuable insights for the biosynthesis of other organic acids.IMPORTANCEThis study focuses on enhancing L-malic acid synthesis by modifying the tricarboxylic acid cycle within the mitochondria of Aspergillus niger. We emphasize the significant role of fumarase in converting fumaric acid into L-malic acid, enhancing our understanding of metabolic pathways in A. niger. The precise regulation of fumA is highlighted as a key factor in enhancing L-malic acid production. Furthermore, this research introduces a stringent conditional promoter (PmfsA), exclusively activated by CaCO3. The utilization of PmfsA for fumA expression resulted in heightened L-malic acid titers. The progress in metabolic engineering and bioprocess optimization holds promise for expediting industrial L-malic acid synthesis via biological fermentation. Moreover, it carries implications for the biosynthesis of various other organic acids.

The clinicopathologic and molecular features, and treatment outcome of fumarate hydratase-deficient renal cell carcinoma: a retrospective comparison with type 2 papillary renal cell carcinoma.

BACKGROUND: To compare clinicopathologic, molecular features, and treatment outcome between fumarate hydratase-deficient renal cell carcinoma (FH-dRCC) and type 2 papillary renal cell carcinoma (T2 pRCC). METHODS: Data of T2 pRCC patients and FH-dRCC patients with additional next-generation sequencing information were retrospectively analyzed. The cancer-specific survival (CSS) and disease-free survival (DFS) were primary endpoint. RESULTS: A combination of FH and 2-succino-cysteine (2-SC) increased the rate of negative predictive value of FH-dRCC. Compared with T2 pRCC cases, FH-dRCC cases displayed a greater prevalence in young patients, a higher frequency of radical nephrectomy. Seven FH-dRCC and two T2 pRCC cases received systemic therapy. The VEGF treatment was prescribed most frequently, with an objective response rate (ORR) of 22.2% and a disease control rate (DCR) of 30%. A combined therapy with VEGF and checkpoint inhibitor reported an ORR of 40% and a DCR of 100%. FH-dRCC cases showed a shortened CSS (P = 0.042) and DFS (P < 0.001). The genomic sequencing revealed 9 novel mutations. CONCLUSIONS: Coupled with genetic detection, immunohistochemical biomarkers (FH and 2-SC) can distinguish the aggressive FH-dRCC from T2 pRCC. Future research is awaited to illuminate the association between the novel mutations and the clinical phenotypes of FH-dRCC in the disease progression.

The role of promoter methylation of the genes encoding the enzymes metabolizing di- and tricarboxylic acids in the regulation of plant respiration by light.

We discuss the role of epigenetic changes at the level of promoter methylation of the key enzymes of carbon metabolism in the regulation of respiration by light. While the direct regulation of enzymes via modulation of their activity and post-translational modifications is fast and readily reversible, the role of cytosine methylation is important for providing a prolonged response to environmental changes. In addition, adenine methylation can play a role in the regulation of transcription of genes. The mitochondrial and extramitochondrial forms of several enzymes participating in the tricarboxylic acid cycle and associated reactions are regulated via promoter methylation in opposite ways. The mitochondrial forms of citrate synthase, aconitase, fumarase, NAD-malate dehydrogenase are inhibited while the cytosolic forms of aconitase, fumarase, NAD-malate dehydrogenase, and the peroxisomal form of citrate synthase are activated. It is concluded that promoter methylation represents a universal mechanism of the regulation of activity of respiratory enzymes in plant cells by light. The role of the regulation of the mitochondrial and cytosolic forms of respiratory enzymes in the operation of malate and citrate valves and in controlling the redox state and balancing the energy level of photosynthesizing plant cells is discussed.

Multiple cutaneous and uterine leiomyomatosis: Reed's syndrome.

Reed's syndrome (RS) is a rare autosomal-dominant disorder characterised by multiple cutaneous and uterine leiomyomas, with a strong tendency for renal cell carcinoma (RCC) development. A woman in her 50s, who had previously undergone total abdominal hysterectomy due to multiple uterine leiomyomas, presented with painful nodules on her trunk and right arm for the past 6 years. These nodules were confirmed as leiomyomas through histopathology. Diagnosis of RS was established through clinicopathological correlation and positive family history, particularly her mother's. Early-onset uterine leiomyomas in patients with a similar family history should raise suspicion for RS, necessitating vigilant long-term follow-up. RCC detection requires mandatory renal imaging. Screening family members and providing genetic counselling are crucial.

Aggressive renal cell carcinoma with biphasic papillary and solid clear cell features harboring IDH2 (R172M) mutation.

Renal cell carcinoma (RCC) is fundamentally a metabolic disease, and RCC associated with mutation of the Krebs cycle enzyme genes include fumarate hydratase-deficient and succinate dehydrogenase-deficient RCC. Most recently, the mutation of isocitrate dehydrogenase 2 (IDH2) has been suggested as the third Krebs cycle enzyme alteration to be associated with oncometabolite-induced RCC tumorigenesis. Herein, we report the second case of RCC harboring an IDH2 (R127M) mutation identified by targeted next-generation sequencing and further confirmed by reverse transcription polymerase chain reaction and Sanger sequencing. This tumor demonstrated a distinctive biphasic morphology, characterized by mixture of a clear cells solid component and an eosinophilic papillary component. These two components were intermingled and formed variably sized nodular or nested structures. Unfavorable histologic features, including infiltration into the perirenal and renal sinus adipose tissues, high nuclei grade, rhabdoid tumor cells, and focal tumor necrosis, were observed. The patient had local lymph nodes metastases at diagnosis and developed brain metastases 3 months after the surgery. This peculiar case provides further insights into RCCs harboring IDH2 mutations.

Fumarate Hydratase-Deficient Leiomyoma of the Uterine Corpus: Comparative Morphologic Analysis of Protein-Deficient Tumors With and Without Pathogenic Germline Fumarate Hydratase Gene Mutations.

Deficiency of fumarate hydratase (FH) protein expression in uterine corpus leiomyomas may be attributable to either germline or somatic mutations of the FH gene, the former being definitional for the hereditary leiomyomatosis and renal cell cancer syndrome. The authors assess whether, using previously reported FH-associated morphologic features, FH protein-deficient uterine corpus leiomyomas associated with a pathogenic germline mutations of the FH gene (group 1) are distinguishable from FH protein-deficient uterine corpus leiomyomas without such mutations (and whose FH protein loss is presumed to be attributable to somatic/epigenetic inactivation or other unknown phenomena: group 2). Groups 1 and 2 were compared regarding a variety of clinicopathologic features, including 7 core "FH-associated" tumoral morphologic features: staghorn vasculature; alveolar-type edema; bizarre nuclei; chain-like tumor nuclei; hyaline cytoplasmic globules; prominent nucleoli, intranuclear inclusions, and perinucleolar halos; and prominent eosinophilic/fibrillary cytoplasm. Among 2418 patients diagnosed with uterine corpus leiomyoma during the study period, FH-associated morphologic features were reported in 1.5% (37 patients), and FH immunohistochemistry was performed in 29 (1.19%). Fourteen (48.27%) of the 29 patients showed FH protein deficiency by immunohistochemistry. Twelve patients underwent germline testing, of which 8 (66.7%) were classified as group 1 and 4 (33.3%) as group 2. FH protein-deficient tumors were larger (10.44 vs 4.08 cm, P = 0.01) and associated with younger patients (42.05 vs 47.97, P = 0.004) than 370 randomly selected uterine leiomyoma controls. Groups 1 and 2 showed no significant differences in patient age and tumor size. In group 1 tumors, the FH-associated morphologic features were generally present diffusely; all group 1 tumors displayed ≥5 FH-associated features, whereas all group 2 tumors displayed <5 FH-associated features (means 6.5 ± 0.53 vs 3.5 ± 1.00, P < 0.001). Notably, eosinophilic/fibrillary cytoplasm and alveolar-type edema were each significantly more prevalent in group 1 tumors than group 2 tumors (P = 0.018 for both). No single morphologic feature was found to be completely sensitive and specific in making the distinction between group 1 and 2 tumors. Our findings suggest that groups 1 and 2 are unlikely to be morphologically distinguishable by individual morphologic features. Whether there is a combination of features that can reliably make this distinction is unclear and will require additional studies with larger cohorts.

Diffuse Carbonic Anhydrase 9 and GATA3 Expression in Fumarate Hydratase Deficient Renal Cell Carcinoma - A Case Report and Immunoprofile Review.

Fumarate hydratase deficient renal cell carcinoma (FHRCC) can exhibit a heterogenous immunoprofile. In the present case, a solitary 10.5 cm mixed cystic and solid left kidney tumor showed various growth patterns, involving renal sinus adipose tissue and the renal pelvis. Tumor cells showed prominent nucleoli and perinucleolar halos. Aberrant diffuse (>90%), strong, and membranous carbonic anhydrase 9 and variable GATA3 expression were present. Diagnostic loss of fumarate hydratase expression and 2-succinyl cysteine overexpression (cytoplasmic and nuclear) were identified. Carbonic anhydrase 9 and GATA3 expression in FHRCC is rarely reported in the literature, and may cause misdiagnosis of clear cell RCC and/or urothelial carcinoma.

The use of Clinicopathological, immunohistochemistry and molecular detection in the diagnosis of fumarate hydratase-deficient uterine leiomyomas.

BACKGROUND: Fumarate hydratase-deficient uterine leiomyomas (FH-dUL) are rare, accounting for only 0.4-1.6% of uterine leiomyomas. FH germline mutation gene is associated with hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC). METHODS: In this study, we aim to investigate Clinicopathological features and FH mutation in FH-dUL. We performed a retrospective analysis of 300 cases of uterine leiomyoma, diagnosed from January 2017 to December 2021, within the archives of the Department of Pathology at Peking University People's Hospital. In our review of the immunohistochemical(IHC) staining was performed on 300 uSMTs to detect FH deficiency. RESULTS: We identified 21cases (21/300,7%) of FH-dUL. Nineteen cases (6.33%) displayed negative FH. Twenty-one cases (7%) displayed 2SC diffuse plasma and nuclear staining. The most common FH-d morphological features included staghorn vasculature ( 100%,21/21), alveolar-pattern oedema (71.43%, 15/21), scattered bizarre nuclei (23.81%, 5/21), eosinophilic cytoplasmic (rhabdoid) inclusions (47.62%, 10/21), significant eosinophilic nucleolus with peri-nucleolus hollowing (23.81%, 5/21), ovoid nuclei sometimes arranged in chains (9.52%, 2/21). DNA sequencing for the 21 cases was performed using Next Generation Sequencing (NGS). 6 cases were detected significant variations for the FH gene, 11 cases were detected FH gene mutation forvariants of uncertain significance (VUS), and 2 cases were detected a TP53 gene mutation. No related mutations were detected in the other two cases. CONCLUSIONS: FH-dUL is rare. The combination of predictive Clinicopathological evaluation,FH and 2SC IHC test, and molecular test were helpful for the screening of FH-dUL from uSMTs,or even the screening of HLRCC.

Malignant glomus tumor arising in association with a fumarate hydratase-deficient leiomyoma: An unusual collision tumor.

Collision tumors, defined as "two independent neoplasms that occur in close proximity to one another but maintain distinct boundaries," are quite rare. We report an exceptional collision tumor composed of a genetically confirmed malignant glomus tumor and a fumarate hydratase (FH)-deficient leiomyoma, presenting as a subcutaneous thigh mass in a 38-year-old male who was known to have hereditary leiomyomatosis and renal cell carcinoma syndrome. Microscopic examination identified a biphasic subcutaneous mass comprising sheets and nodules of glomus cells, with nuclear atypia and mitotic activity, and fascicles of mitotically inactive smooth muscle with variably pleomorphic nuclei and intracytoplasmic eosinophilic inclusions, features of FH-deficient leiomyoma. Immunohistochemistry demonstrated loss of FH and robust 2-succinocysteine expression in the smooth muscle, with a normal (FH-retained) expression pattern in the glomus tumor. Next-generation sequencing, performed on the glomus tumor component, identified CARMN::NOTCH2 fusion, characteristic of malignant glomus tumors. Awareness of the distinctive morphologic, immunohistochemical, and molecular genetic features of glomus tumors and FH-deficient leiomyomas is important for correct clinical management of patients with exceptional collision tumors of this type.

Interchangeability of class I and II fumarases in an obligate methanotroph Methylotuvimicrobium alcaliphilum 20Z.

The methanotrophic bacterium Methylotuvimicrobium alcaliphilum 20Z is an industrially promising candidate for bioconversion of methane into value-added chemicals. Here, we have study the metabolic consequences of the breaking in the tricarboxylic acid (TCA) cycle by fumarase knockout. Two fumarases belonging to non-homologous class I and II fumarases were obtained from the bacterium by heterologous expression in Escherichia coli. Class I fumarase (FumI) is a homodimeric enzyme catalyzing the reversible hydration of fumarate and mesaconate with activities of ~94 and ~81 U mg-1 protein, respectively. The enzyme exhibited high activity under aerobic conditions, which is a non-typical property for class I fumarases characterized to date. The calculation of kcat/S0.5 showed that the enzyme works effectively with either fumarate or mesaconate, but it is almost four times less specific to malate. Class II fumarase (FumC) has a tetrameric structure and equal activities of both fumarate hydration and malate dehydration (~45 U mg-1 protein). Using mutational analysis, it was shown that both forms of the enzyme are functionally interchangeable. The triple mutant strain 20Z-3E (ΔfumIΔfumCΔmae) deficient in the genes encoding the both fumarases and the malic enzyme accumulated 2.6 and 1.1 mmol g-1 DCW fumarate in the medium when growing on methane and methanol, respectively. Our data suggest the redundancy of the metabolic node in the TCA cycle making methanotroph attractive targets for modification, including generation of strains producing the valuable metabolites.

Fumarate hydratase (FH) and cancer: a paradigm of oncometabolism.

Fumarate hydratase (FH) is an enzyme of the Tricarboxylic Acid (TCA) cycle whose mutations lead to hereditary and sporadic forms of cancer. Although more than twenty years have passed since its discovery as the leading cause of the cancer syndrome Hereditary leiomyomatosis and Renal Cell Carcinoma (HLRCC), it is still unclear how the loss of FH causes cancer in a tissue-specific manner and with such aggressive behaviour. It has been shown that FH loss, via the accumulation of FH substrate fumarate, activates a series of oncogenic cascades whose contribution to transformation is still under investigation. In this review, we will summarise these recent findings in an integrated fashion and put forward the case that understanding the biology of FH and how its mutations promote transformation will be vital to establish novel paradigms of oncometabolism.

Enantioselectivity in the enzymatic dehydration of malate and tartrate: Mirror image specificities of structurally similar dehydratases.

Malate (2-hydroxysuccinic acid) and tartrate (2,3-dihydroxysuccinic acid) are chiral substrates; the former existing in two enantiomeric forms (R and S) while the latter exists as three stereoisomers (R,R; S,S; and R,S). Dehydration by stereospecific hydrogen abstraction and antielimination of the hydroxyl group yield the achiral products fumarate and oxaloacetate, respectively. Class-I fumarate hydratase (FH) and L-tartrate dehydratase (L-TTD) are two highly conserved enzymes belonging to the iron-sulfur cluster hydrolyase family of enzymes that catalyze reactions on specific stereoisomers of malate and tartrate. FH from Methanocaldococcus jannaschii accepts only (S)-malate and (S,S)-tartrate as substrates while the structurally similar L-TTD from Escherichia coli accepts only (R)-malate and (R,R)-tartrate as substrates. Phylogenetic analysis reveals a common evolutionary origin of L-TTDs and two-subunit archaeal FHs suggesting a divergence during evolution that may have led to the switch in substrate stereospecificity preference. Due to the high conservation of their sequences, a molecular basis for switch in stereospecificity is not evident from analysis of crystal structures of FH and predicted structure of L-TTD. The switch in enantiomer preference may be rationalized by invoking conformational plasticity of the amino acids interacting with the substrate, together with substrate reorientation and conformer selection about the C2C3 bond of the dicarboxylic acid substrates. Although classical models of enzyme-substrate binding are insufficient to explain such a phenomenon, the enantiomer superposition model suggests that a minor reorientation in the active site residues could lead to the switch in substrate stereospecificity.

The Role of Morphology in Predicting Fumarate Hydratase-deficient Uterine Leiomyomas in Young Women.

Hereditary leiomyomatosis and renal cell carcinoma is caused by germline mutations in the fumarate hydratase (FH) gene and is associated with an increased incidence of leiomyomas and a potentially aggressive variant of renal cell carcinoma. Pathologic evaluation of uterine leiomyoma can provide an opportunity for early recognition of the syndrome. We reviewed all archived slides of the cases to identify the characteristic morphologic features described for FH-deficient leiomyomas. We performed immunohistochemistry on whole sections of patients with uterine leiomyoma to evaluate for both FH and 2-succinocysteine (2SC) expression. Of the 106 cases, 19 showed the characteristic eosinophilic nucleoli with perinuclear halos, and 24 revealed a characteristic eosinophilic cytoplasmic inclusion consisting of pink globules present within the cytoplasm. Both of these morphologic findings were present together in 15 cases, and hemangiopericytomatous vessels were detected in 23 cases. The loss of FH protein expression was detected in 14 out of 106 cases (13%), and 13 out of 106 cases (12%) were positive for 2SC. We detected 10 cases with both 2SC-positive and FH expression loss. The presence of eosinophilic nucleoli with perinuclear halos and eosinophilic cytoplasmic inclusion was associated with both loss of FH protein expression and 2SC positivity ( P < 0.001). These findings underscore the importance of hematoxylin and eosin-based predictive morphology in FH-deficient uterine leiomyomas. Therefore, morphologic assessment of uterine leiomyomas for features of FH deficiency can serve as a screening tool for hereditary leiomyomatosis and renal cell carcinoma syndrome, allowing patients to be divided according to their hereditary risk assessment.