title: Loss of SDHB Elevates Catecholamine Synthesis and Secretion Depending on ROS Production and HIF Stabilization.
abstract: Germline mutations in genes encoding succinate dehydrogenase subunits are associated with the development of familial pheochromocytomas and paragangliomas [hereditary paraganglioma/pheochromocytoma syndrome (HPPS)]. In particular, a mutation in succinate dehydrogenase subunit B (SDHB) is highly associated with abdominal paraganglioma and subsequent distant metastasis (malignant paraganglioma), indicating the importance of SDHB genetic testing. The discovery of HPPS suggests an association among genetic mitochondrial defects, tumor development, and catecholamine oversecretion. To investigate this association, we transfected pheochromocytoma cells (PC12) with SDHB-specific siRNA. SDHB silencing virtually abolished complex II activity, demonstrating the utility of this in vitro model for investigating the pseudo-hypoxic drive hypothesis. Lack of complex II activity resulting from RNA interference of SDHB increased tyrosine hydroxylase (TH; the rate-limiting enzyme in catecholamine biosynthesis) activity and catecholamine secretion. Reduced apoptosis was observed accompanied by Bcl-2 accumulation in PC12 cells, consistent with the phenotypes of paragangliomas with SDHB mutations. In addition, SDHB silencing increased reactive oxygen species (ROS) production and nuclear HIF1α stabilization under normoxic conditions. Furthermore, phenotypes induced by complex II activity knockdown were abolished by pretreatment with N-acetyl cysteine (an ROS scavenger) and by prior HIF1α knockdown, indicating an ROS- and HIF1α-dependent mechanism. Our results indicate that increased ROS may act as signal transduction messengers that induce HIF1α stabilization and may be necessary for the pseudo-hypoxic states observed in our experimental model. To our knowledge, this is the first study demonstrating that pseudo-hypoxic states resulting from SDHB knockdown are associated with increased TH activity and catecholamine oversecretion.
authors.affiliation: Department of Molecular Laboratory Medicine, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Yuria
authors.initials: Y
authors.lastname: Saito
authors.affiliation: Department of Disease Control and Homeostasis, Kanazawa University Graduate School of Medical Science, Kanazawa, Japan.
authors.forename: Kiyo-Aki
authors.initials: KA
authors.lastname: Ishii
authors.affiliation: Department of Molecular Laboratory Medicine, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Aita
authors.affiliation: Department of Breast-Thyroid-Endocrine Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Ikeda
authors.affiliation: Department of Molecular Laboratory Medicine, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kawakami
authors.affiliation: Department of Internal Medicine (Endocrinology and Metabolism), Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shimano
authors.affiliation: Department of Breast-Thyroid-Endocrine Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Hisato
authors.initials: H
authors.lastname: Hara
authors.affiliation: Division of Sports Science, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan. K-takemd@md.tsukuba.ac.jp.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Takekoshi
mesh_terms: D000818:Animals; D017209:Apoptosis; D002395:Catecholamines / Q000096:biosynthesis* / Q000378:metabolism; D002470:Cell Survival; D042963:Electron Transport Complex II / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D009154:Mutation; D016716:PC12 Cells; D010235:Paraganglioma / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013385:Succinate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
chemical_list: D002395:Catecholamines; C497444:Hif1a protein, rat; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D014446:Tyrosine 3-Monooxygenase; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase
keywords: Catecholamine; Hereditary paraganglioma/pheochromocytoma syndrome; Reactive oxygen species; Succinate dehydrogenase