Interaction between hypoxia and mutations in SDH subunit genes associated with phaeochromocytoma/paragangliomas — ASN Events
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  3. Interaction between hypoxia and mutations in SDH subunit genes associated with phaeochromocytoma/paragangliomas

Interaction between hypoxia and mutations in SDH subunit genes associated with phaeochromocytoma/paragangliomas (#10)

Venessa HM Tsang 1 2 , Nicole Parker 1 2 , Juan Carlos Cassano 1 , Trisha Dwight 1 2 , Carolyn M Sue 1 2 , David Veivers 1 3 , Bruce G Robinson 1 2 , Diana E Benn 1 2 , Roderick J Clifton-Bligh 1 2
  1. Kolling Institute, St Leonards, NSW, Australia
  2. University of Sydney, Sydney, NSW, Australia
  3. Ear Nose and Throat Surgery, Royal North Shore Hospital, St Lenoards, NSW, Australia

Introduction

Phaeochromocytomas (PC) and paragangliomas occur in the context of inherited syndromes in 30% of cases1. Of 11 loci that have been defined to date, 4 encode succinate dehydrogenase genes (SDHA, SDHB, SDHC, and SDHD, collectively SDHx). Mechanisms by which germline SDHx mutations stimulate tumour formation are poorly understood. Clinical data implicate an interaction with environmental hypoxia.2, 3, 4 This study investigated effects of hypoxia on cellular function in the presence or absence of SDHx mutation.

Methods

1. Wild type and mutant SDHx cDNAs tagged with GFP were expressed in HEK293 cells, and cultured in either normoxic or hypoxic conditions. Cellular localisation was visualised by confocal microscopy and confirmed by western blotting.
2. Mitochondrial function was studied in a novel model5 of SDHx dysfunction using neural stem cells obtained from patients with SDHx mutations.
3. The hypoxic-responsive miR2106 was previously measured by qPCR in PC/PGLs containing mutations in SDHB and non SDHB PC/PGLs. MiR210 was also measured in neurospheres.

Results

Wild-type SDHx localised to mitochondriae under normoxic conditions, but less so under hypoxia. In contrast, some SDHx mutants constitutively failed to localise to mitochondriae whereas other mutants retained mitochondrial localisation in normoxic but not hypoxic conditions.
Neurosphere cells containing SDHB mutations exhibited reduced SDHB expression, reduced complex II function, and increased membrane potential.
MiR210 levels were increased in SDHB-mutated tumours compared with non-SDHB-mutated tumours or normal samples. MiR210 was increased in neurospheres containing SDHB mutations.

Conclusions

1. SDHx mutations impaired SDHx mitochondrial localisation, either constitutively or in conjunction with hypoxia.
2. The neurosphere model confirmed that some complex II dysfunction is evident with heterozygous SDHB mutation.
3. Elevated miR210 was evident in PC/PGLs associated with SDHB mutations, consistent with known pseudohypoxic gene signature of these tumours.
Our study suggests an interaction between SDHx mutation and hypoxia in the pathogenesis of PC/PGL.

  1. Benn D, Gimenez-Roqueplo A, Reilly J, al. e. 2006 Clinical Presentation and Penetrance of Pheochromocytoma/Paraganglioma Syndomres. Journal of Clinical Endocrinology and Metabolism 91:827-36.
  2. Astrom K, Cohen JE, Willett-Brozick JE, Aston CE, Baysal BE. 2003 Altitude is a phenotypic modifier in hereditary paraganglioma type 1: evidence for an oxygen-sensing defect. Hum Genet 113(3):228-37.
  3. Favier J, Gimenez-Roqueplo AP. 2010 Pheochromocytomas: the (pseudo)-hypoxia hypothesis. Baillieres Best Pract Res Clin Endocrinol Metab 24(3):401-13 24(6):957-68.
  4. Cerecer-Gil NY, Figuera LE, Llamas FJ, Lara M, Escamilla JG, Ramos R, Estrada G, Hussain AK, Gaal J, Korpershoek E, de Krijger RR, Dinjens WNM, Devilee P, Bayley JP. 2010 Mutation of SDHB is a Cause of Hypoxia-Related High-Altitude Paraganglioma. Clinical Cancer Research 16(16):4148-54.
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  6. Huang X, Le Q-T, Giaccia AJ. 2010 MiR-210 - micromanager of the hypoxia pathway. Trends in Molecular Medicine 16(5):230-7.