Succinate dehydrogenase is a key enzyme in the tricarboxylic acid cycle and the electron transport chain. All four subunits of succinate dehydrogenase are tumor suppressor genes predisposing to ...paraganglioma, but only mutations in the SDHB subunit are associated with increased risk of metastasis. Here we generated an
knockout chromaffin cell line and compared it with
deficient cells. Both cell types exhibited similar SDH loss of function, metabolic adaptation, and succinate accumulation. In contrast,
cells showed hallmarks of mesenchymal transition associated with increased DNA hypermethylation and a stronger pseudo-hypoxic phenotype compared with
cells. Loss of SDHB specifically led to increased oxidative stress associated with dysregulated iron and copper homeostasis in the absence of NRF2 activation. High-dose ascorbate exacerbated the increase in mitochondrial reactive oxygen species, leading to cell death in
cells. These data establish a mechanism linking oxidative stress to iron homeostasis that specifically occurs in
-deficient cells and may promote metastasis. They also highlight high-dose ascorbate as a promising therapeutic strategy for SDHB-related cancers. SIGNIFICANCE: Loss of different succinate dehydrogenase subunits can lead to different cell and tumor phenotypes, linking stronger 2-OG-dependent dioxygenases inhibition, iron overload, and ROS accumulation following SDHB mutation.
Pheochromocytomas and paragangliomas (PCCs/PGLs) are neural crest-derived tumours with a very strong genetic component. Here we report the first integrated genomic examination of a large collection ...of PCC/PGL. SNP array analysis reveals distinct copy-number patterns associated with genetic background. Whole-exome sequencing shows a low mutation rate of 0.3 mutations per megabase, with few recurrent somatic mutations in genes not previously associated with PCC/PGL. DNA methylation arrays and miRNA sequencing identify DNA methylation changes and miRNA expression clusters strongly associated with messenger RNA expression profiling. Overexpression of the miRNA cluster 182/96/183 is specific in SDHB-mutated tumours and induces malignant traits, whereas silencing of the imprinted DLK1-MEG3 miRNA cluster appears as a potential driver in a subgroup of sporadic tumours. Altogether, the complete genomic landscape of PCC/PGL is mainly driven by distinct germline and/or somatic mutations in susceptibility genes and reveals different molecular entities, characterized by a set of unique genomic alterations.
Context:
Pheochromocytoma-paraganglioma syndrome is caused by mutations in SDHB, SDHC, and SDHD, encoding subunits of succinate dehydrogenase (SDH), and in SDHAF2, required for flavination of SDHA. A ...recent report described a patient with an abdominal paraganglioma, immunohistochemically negative for SDHA, and identified a causal germline mutation in SDHA.
Objective:
In this study, we evaluated the significance of SDHA immunohistochemistry in the identification of new patients with SDHA mutations.
Setting:
This study was performed in the Erasmus Medical Center in Rotterdam (The Netherlands) and the Université Paris Descartes in Paris (France).
Methods:
We investigated 316 pheochromocytomas and paragangliomas for SDHA expression. Sequence analysis of SDHA was performed on all tumors that were immunohistochemically negative for SDHA and on a subset of tumors immunohistochemically positive for SDHA.
Results:
Six tumors were immunohistochemically negative for SDHA. Four tumors from Dutch patients showed a germline c.91C→T SDHA gene mutation (p.Arg31X). Another tumor (from France) carried a germline SDHA missense mutation c.1753C→T (p.Arg585Trp). Loss of the wild-type SDHA allele was confirmed by loss of heterozygosity analysis. Sequence analysis of 35 SDHA immunohistochemically positive tumors did not reveal additional SDHA mutations.
Conclusions:
Our results demonstrate that SDHA immunohistochemistry on paraffin-embedded tumors can reveal the presence of SDHA germline mutations and allowed the identification of SDHA-related tumors in at least 3% of patients affected by apparently sporadic (para)sympathetic paragangliomas and pheochromocytomas.
Germline mutations in the RET, SDHA, SDHAF2, SDHB, SDHC, SDHD, MAX, TMEM127, NF1 or VHL genes are identified in about 30% of patients with pheochromocytoma or paraganglioma and somatic mutations in ...RET, VHL or MAX genes are reported in 17% of sporadic tumors. In the present study, using mutation screening of the NF1 gene, mapping of chromosome aberrations by single nucleotide polymorphism (SNP) array, microarray-based expression profiling and immunohistochemistry (IHC), we addressed the implication of NF1 somatic alterations in pheochromocytomas and paragangliomas. We studied 53 sporadic tumors, selected because of their classification with RET/NF1/TMEM127-related tumors by genome wide expression studies, as well as a second set of 11 independent tumors selected on their low individual levels of NF1 expression evaluated by microarray. Direct sequencing of the NF1 gene in tumor DNA identified the presence of an inactivating NF1 somatic mutation in 41% (25/61) of analyzed sporadic tumors, associated with loss of the wild-type allele in 84% (21/25) of cases. Gene expression signature of NF1-related tumors highlighted the downregulation of NF1 and the major overexpression of SOX9. Among the second set of 11 tumors, two sporadic tumors carried somatic mutations in NF1 as well as in another susceptibility gene. These new findings suggest that NF1 loss of function is a frequent event in the tumorigenesis of sporadic pheochromocytoma and strengthen the new concept of molecular-based targeted therapy for pheochromocytoma or paraganglioma.
The Warburg effect describes how cancer cells down-regulate their aerobic respiration and preferentially use glycolysis to generate energy. To evaluate the link between hypoxia and Warburg effect, we ...studied mitochondrial electron transport, angiogenesis and glycolysis in pheochromocytomas induced by germ-line mutations in VHL, RET, NF1 and SDH genes. SDH and VHL gene mutations have been shown to lead to the activation of hypoxic response, even in normoxic conditions, a process now referred to as pseudohypoxia. We observed a decrease in electron transport protein expression and activity, associated with increased angiogenesis in SDH- and VHL-related, pseudohypoxic tumors, while stimulation of glycolysis was solely observed in VHL tumors. Moreover, microarray analyses revealed that expression of genes involved in these metabolic pathways is an efficient tool for classification of pheochromocytomas in accordance with the predisposition gene mutated. Our data suggest an unexpected association between pseudohypoxia and loss of p53, which leads to a distinct Warburg effect in VHL-related pheochromocytomas.
Pheochromocytomas: The (pseudo)-hypoxia hypothesis Favier, Judith, PhD; Gimenez-Roqueplo, Anne-Paule, MD, PhD
Best Practice & Research Clinical Endocrinology & Metabolism,
12/2010, Letnik:
24, Številka:
6
Journal Article
Recenzirano
Hypoxia and pheochromocytoma/paraganglioma have a long common history. Since the description, almost 40 years ago, of an increased incidence of head and neck paragangliomas in chronic hypoxia, ...discoveries on oxygen-sensing and on hereditary paraganglioma in the beginning of years 2000 provided the proof of concept of a strong link between these neuroendocrine tumors and the hypoxic pathway. It was demonstrated that both SDH and VHL genes mutations lead to the abnormal stabilization and activation of hypoxia-inducible factors, and to the subsequent regulation of multiple target genes, the products of which are implicated in proliferation, apoptosis, angiogenesis, energy metabolism or invasiveness and metastases. Altogether, physiological, genetic, cellular and molecular data collected over years all point to a central role of the hypoxic or pseudohypoxic pathway in pheochromocytoma and paraganglioma tumorigenesis.
Research focused on succinate dehydrogenase (SDH) and its substrate, succinate, culminated in the 1950s accompanying the rapid development of research dedicated to bioenergetics and intermediary ...metabolism. This allowed researchers to uncover the implication of SDH in both the mitochondrial respiratory chain and the Krebs cycle. Nowadays, this theme is experiencing a real revival following the discovery of the role of SDH and succinate in a subset of tumors and cancers in humans. The aim of this review is to enlighten the many questions yet unanswered, ranging from fundamental to clinically oriented aspects, up to the danger of the current use of SDH as a target for a subclass of pesticides.
Pheochromocytoma and paraganglioma (PPGL) are rare neuroendocrine tumors, associated with highly variable postoperative evolution. The scarcity of reliable PPGL prognostic markers continues to ...complicate patient management. In this study, we explored genome-wide DNA methylation patterns in the context of PPGL malignancy to identify novel prognostic markers.
We retrospectively investigated DNA methylation patterns in PPGL with and without metastases using high-throughput DNA methylation profiling data (Illumina 27K) from two large, well-characterized discovery (n = 123; 24 metastatic) and primary validation (n = 154; 24 metastatic) series. Additional validation of candidate CpGs was performed by bisulfite pyrosequencing in a second independent set of 33 paraffin-embedded PPGLs (19 metastatic).
Of the initial 86 candidate CpGs, we successfully replicated 52 (47 genes), associated with metastatic PPGL. Of these, 48 CpGs showed significant associations with time to progression even after correcting for SDHB genotype, suggesting their value as prognostic markers independent of genetic background. Hypermethylation of RDBP (negative elongation factor complex member E) in metastatic tumors was further validated by bisulfite pyrosequencing Δβmetastatic-benign = 0.29, P = 0.003; HR, 1.4; 95% confidence interval (CI), 1.1-2.0; P = 0.018 and may alter transcriptional networks involving (RERG, GPX3, and PDZK1) apoptosis, invasion, and maintenance of DNA integrity.
This is the first large-scale study of DNA methylation in metastatic PPGL that identifies and validates prognostic markers, which could be used for stratifying patients according to risk of developing metastasis. Of the three CpGs selected for further validation, one (RDBP) was clearly confirmed and could be used for stratifying patients according to the risk of developing metastases.
Context:
Patients with pheochromocytoma (PH) or paraganglioma (PGL) may suffer from tumor persistence or recurrence after resection of the primary tumor. Malignancy and genetic determinants account ...for the vast majority of these cases, but tumor recurrence or persistence may also arise from tumor spillage during primary resection, followed by peritoneal implantation. We report here five such cases.
Materials and Methods:
Thirty-nine of the 181 patients referred to our unit for a PH experienced tumor persistence or recurrence as a result of malignant disease (n = 12), new PGL in a context of genetic determinants (n = 18) or incomplete primary surgical resection (n = 4). Another five patients presenting with adrenal PH could not be categorized into these three groups.
Results and Discussion:
All five patients (age range 45–63 years) presented evidence of tumor capsule rupture documented upon macroscopic examination or in the surgical report. Initial diagnostic examinations provided no evidence of malignancy. All had a period of apparent remission, lasting from 24 to 106 months. The principal site of recurrence was invariably the peritoneum or the retroperitoneum. Two patients suffered solid organ metastasis, involving the liver (n = 2), bones (n = 1), and lung (n = 1). Therapeutic management involved a combination of 131I-metaiodobenzylguanidine therapy and surgery. Two patients died due to tumor progression. One patient experienced tumor progression despite surgery. Two patients are currently in a satisfactory condition.
Conclusion:
Tumor rupture during surgical resection, with subsequent peritoneal and retroperitoneal dissemination, is a potentially lethal complication of primary pheochromocytoma resection. Even in cases of apparently benign disease, it may lead to peritoneal carcinomatosis and metastatic disease. Complete primary surgery is, therefore, crucial for a good prognosis in PH patients. Furthermore, in cases of tumor rupture, careful follow-up is mandatory, because recurrences may occur after long periods of apparent remission.
Angiopoietin-1 (Ang1) and -2 (Ang2) are endothelial growth factors that bind to the tyrosine kinase receptor Tie2 and contribute to orchestrate blood vessel formation during angiogenesis. Ang1 ...mediates vessel maturation and integrity by the recruitment of pericytes. In contrast, Ang2 is classically considered as a Tie2 antagonist, counteracting the stabilizing action of Ang1. Inflammation exists in a mutually dependent association with angiogenesis and we have therefore studied the capacity of angiopoietins to modulate proinflammatory activities, namely P-selectin translocation and neutrophil adhesion onto endothelial cells. We observed that both Ang1 and Ang2 increased these biologic activities. Furthermore, combination of Ang1/Ang2 induced an additive effect on neutrophil adhesion but not on P-selectin translocation. In an attempt to clarify this phenomenon, we found that angiopoietins can directly activate neutrophils through Tie2 signaling as well as modulate platelet-activating factor (PAF) synthesis and β2 integrin functional up-regulation. Together, our data demonstrate that angiopoietins could promote acute recruitment of leukocytes, which might contribute to facilitate vascular remodeling and angiogenesis.
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