La succinate déshydrogénase (SDH) est une enzyme mitochondriale qui participe au cycle de Krebs et à la chaîne respiratoire. Quand elles sont à l’origine de cancers, les mutations des gènes codant ...les différentes sous-unités de la SDH sont responsables d’une prédisposition aux phéochromocytomes et aux paragangliomes, et, plus rarement, aux tumeurs stromales gastro-intestinales ou au cancer du rein. Une diminution de l’activité de la SDH, non expliquée par la génétique, s’observe aussi dans certains cancers plus fréquents. Une des conséquences de l’inactivation de la SDH est la production excessive de son substrat, le succinate, qui joue un rôle d’oncométabolite en promouvant un statut pseudohypoxique et d’importants remaniements épigénétiques. La compréhension de l’oncogenèse liée à la succinate déshydrogénase permet aujourd’hui de développer des méthodes diagnostiques innovantes et d’envisager des thérapies ciblées pour la prise en charge des patients atteints.
Succinate dehydrogenase (SDH) is a mitochondrial enzyme that participates in both the tricarboxylic acid cycle and the electron transport chain. Mutations in genes encoding SDH are responsible for a predisposition to pheochromocytomas and paragangliomas, and more rarely, to gastrointestinal stromal tumors or renal cell carcinomas. A decrease in SDH activity, not explained by genetics, has also been observed in more common cancers. One of the consequences of the inactivation of SDH is the excessive production of its substrate, succinate, which acts as an oncometabolite by promoting a pseudohypoxic status and an extensive epigenetic rearrangement. Understanding SDH-related oncogenesis now makes it possible to develop innovative diagnostic methods and to consider targeted therapies for the management of affected patients.
Paragangliomas and pheochromocytomas (PPGL) are rare neuroendocrine tumours characterized by a strong genetic determinism. Over the past 20 years, evolution of PPGL genetics has revealed that around ...40% of PPGL are genetically determined, secondary to a germline mutation in one of more than twenty susceptibility genes reported so far. More than half of the mutations occur in one of the SDHx genes (SDHA, SDHB, SDHC, SDHD, SDHAF2), which encode the different subunits and assembly protein of a mitochondrial enzyme, succinate dehydrogenase. These susceptibility genes predispose to early forms (VHL, RET, SDHD, EPAS1, DLST), syndromic (RET, VHL, EPAS1, NF1, FH), multiple (SDHD, TMEM127, MAX, DLST, MDH2, GOT2) or malignant (SDHB, FH, SLC25A11) PPGL. The discovery of a germline mutation in one of these genes changes the patient's follow-up and allows genetic screening of affected families and the presymptomatic follow-up of relatives carrying a mutation.
Experimental models for pheochromocytoma and paraganglioma are needed for basic pathobiology research and for preclinical testing of drugs to improve treatment of patients with these tumors, ...especially patients with metastatic disease. The paucity of models reflects the rarity of the tumors, their slow growth, and their genetic complexity. While there are no human cell line or xenograft models that faithfully recapitulate the genotype or phenotype of these tumors, the past decade has shown progress in development and utilization of animal models, including a mouse and a rat model for SDH-deficient pheochromocytoma associated with germline Sdhb mutations. There are also innovative approaches to preclinical testing of potential treatments in primary cultures of human tumors. Challenges with these primary cultures include how to account for heterogeneous cell populations that will vary depending on the initial tumor dissociation and how to distinguish drug effects on neoplastic vs normal cells. The feasible duration for maintaining cultures must also be balanced against time required to reliably assess drug efficacy. Considerations potentially important for all in vitro studies include species differences, phenotype drift, changes that occur in the transition from tissue to cell culture, and the O2 concentration in which cultures are maintained.
HIF2alpha/EPAS1 is a hypoxia-inducible transcription factor involved in catecholamine homeostasis, vascular remodelling, physiological angiogenesis and adipogenesis. It is overexpressed in many ...cancerous tissues, but its exact role in tumour progression remains to be clarified.
In order to better establish its function in tumourigenesis and tumour angiogenesis, we have stably transfected mouse neuroblastoma N1E-115 cells with the native form of HIF2alpha or with its dominant negative mutant, HIF2alpha (1-485) and studied their phenotype in vitro and in vivo.
In vitro studies reveal that HIF2alpha induces neuroblastoma cells hypertrophy and decreases their proliferation rate, while its inactivation by the HIF2alpha (1-485) mutant leads to a reduced cell size, associated with an accelerated proliferation. However, our in vivo experiments show that subcutaneous injection of cells overexpressing HIF2alpha into syngenic mice, leads to the formation of tumour nodules that grow slower than controls, but that are well structured and highly vascularized. In contrast, HIF2alpha (1-485)-expressing neuroblastomas grow fast, but are poorly vascularized and quickly tend to extended necrosis.
Together, our data reveal an unexpected combination between an antiproliferative and a pro-angiogenic function of HIF2alpha that actually seems to be favourable to the establishment of neuroblastomas in vivo.
Mitochondrial complex II, or succinate dehydrogenase, is a key enzymatic complex involved in both the tricarboxylic acid (TCA) cycle and oxidative phosphorylation as part of the mitochondrial ...respiratory chain. Germline succinate dehydrogenase subunit A (SDHA) mutations have been reported in a few patients with a classical mitochondrial neurodegenerative disease. Mutations in the genes encoding the three other succinate dehydrogenase subunits (SDHB, SDHC and SDHD) have been identified in patients affected by familial or 'apparently sporadic' paraganglioma and/or pheochromocytoma, an autosomal inherited cancer-susceptibility syndrome. These discoveries have dramatically changed the work-up and genetic counseling of patients and families with paragangliomas and/or pheochromocytomas. The subsequent identification of germline mutations in the gene encoding fumarase--another TCA cycle enzyme--in a new hereditary form of susceptibility to renal, uterine and cutaneous tumors has highlighted the potential role of the TCA cycle and, more generally, of the mitochondria in cancer.
Although the alteration of cellular metabolism in cancer was reported by Warburg in the early 1930s, a regain of interest in cancer metabolism has more recently followed the discovery of germline or ...somatic mutations in genes coding for metabolic enzymes (succinate dehydrogenase, fumarate hydratase and isocitrate dehydrogenase) that are associated with tumor susceptibility. Mutations in these genes are found in numerous tumor types including paragangliomas, kidney cancers, leiomyomas, glioblastomas and acute myeloid leukemia. They lead to the accumulation of so‐called oncometabolites that behave as competitors of 2‐oxoglutarate‐dependent dioxygenases, involved in a broad spectrum of pathways such as hypoxic response and epigenetic reprogramming. Here, we review the diverse pathways affected by oncometabolites, their potential role in cancer formation, maintenance, metastasis and sensitivity to chemotherapies, as well as emerging new therapeutic strategies.
Paragangliomas and pheochromocytomas are rare neuroendocrine tumors characterized by a large spectrum of hereditary predisposition. Based on gene expression profiling classification, they can be ...classically assigned to either a hypoxic/angiogenic cluster (cluster 1 including tumors with mutations in
SDHx
,
VHL
and
FH
genes) or a kinase-signaling cluster (cluster 2 consisting in tumors related to
RET
,
NF1
,
TMEM127
and
MAX
genes mutations, as well as most of the sporadic tumors). The past 15 years have seen the emergence of an increasing number of genetically engineered and grafted models to investigate tumorigenesis and develop new therapeutic strategies. Among them, only cluster 2-related predisposed models have been successful but grafted models are however available to study cluster 1-related tumors. In this review, we present an overview of existing rodent models targeting predisposition genes involved or not in human pheochromocytoma/paraganglioma susceptibility and their contribution to the improvement of pheochromocytoma experimental research.
Mitochondrial succinate-coenzyme Q reductase (complex II) consists of four subunits, SDHA, SDHB, SDHC and SDHD. Heterozygous germline mutations in SDHB, SDHC, SDHD and SDHAF2 encoding for succinate ...dehydrogenase (SDH) complex assembly factor 2 cause hereditary paragangliomas and pheochromocytomas. Surprisingly, no genetic link between SDHA and paraganglioma/pheochromocytoma syndrome has ever been established. We identified a heterozygous germline SDHA mutation, p.Arg589Trp, in a woman suffering from catecholamine-secreting abdominal paraganglioma. The functionality of the SDHA mutant was assessed by studying SDHA, SDHB, HIF-1α and CD34 protein expression using immunohistochemistry and by examining the effect of the mutation in a yeast model. Microarray analyses were performed to study gene expression involved in energy metabolism and hypoxic pathways. We also investigated 202 paragangliomas or pheochromocytomas for loss of heterozygosity (LOH) at the SDHA, SDHB, SDHC and SDHD loci by BAC array comparative genomic hybridization. In vivo and in vitro functional studies demonstrated that the SDHA mutation causes a loss of SDH enzymatic activity in tumor tissue and in the yeast model. Immunohistochemistry and transcriptome analyses established that the SDHA mutation causes pseudo-hypoxia, which leads to a subsequent increase in angiogenesis, as other SDHx gene mutations. LOH was detected at the SDHA locus in the patient's tumor but was present in only 4.5% of a large series of paragangliomas and pheochromocytomas. The SDHA gene should be added to the list of genes encoding tricarboxylic acid cycle proteins that act as tumor suppressor genes and can now be considered as a new paraganglioma/pheochromocytoma susceptibility gene.
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