Tumors caused by loss-of-function mutations in genes encoding TCA cycle enzymes have been recently discovered and are now of great interest. Mutations in succinate dehydrogenase (SDH) subunits cause pheochromocytoma/paraganglioma (PCPG) and syndromically associated tumors, which differ phenotypically and clinically from more common SDH-intact tumors of the same types. Consequences of SDH deficiency include rewired metabolism, pseudohypoxic signaling and altered redox balance. PCPG with SDHB mutations are particularly aggressive, and development of treatments has been hampered by lack of valid experimental models. Attempts to develop mouse models have been unsuccessful. Using a new strategy, we developed a xenograft and cell line model of SDH-deficient pheochromocytoma from rats with a heterozygous germline Sdhb mutation. The genome, transcriptome and metabolome of this model, called RS0, closely resemble those of SDHB-mutated human PCPGs, making it the most valid model now available. Strategies employed to develop RS0 may be broadly applicable to other SDH-deficient tumors.
James F Powers, Brent Cochran, James D Baleja, Hadley D Sikes, Andrew D Pattison, Xue Zhang, Inna Lomakin, Annette Shepard-Barry, Karel Pacak, Sun Jin Moon, Troy F Langford, Kassi Taylor Stein, Richard W Tothill, Yingbin Ouyang, and Arthur S Tischler
Trisha Dwight, Edward Kim, Karine Bastard, Diana E Benn, Graeme Eisenhofer, Susan Richter, Massimo Mannelli, Elena Rapizzi, Aleksander Prejbisz, Mariola Pęczkowska, Karel Pacak, and Roderick Clifton-Bligh
Mosaic or somatic EPAS1 mutations are associated with a range of phenotypes including pheochromocytoma and/or paraganglioma (PPGL), polycythemia and somatostatinoma. The pathogenic potential of germline EPAS1 variants however is not well understood. We report a number of germline EPAS1 variants occurring in patients with PPGL, including a novel variant c.739C>A (p.Arg247Ser); a previously described variant c.1121T>A (p.Phe374Tyr); several rare variants, c.581A>G (p.His194Arg), c.2353C>A (p.Pro785Thr) and c.2365A>G (p.Ile789Val); a common variant c.2296A>C (p.Thr766Pro). We performed detailed functional studies to understand their pathogenic role in PPGL. In transient transfection studies, EPAS1/HIF-2α p.Arg247Ser, p.Phe374Tyr and p.Pro785Thr were all stable in normoxia. In co-immunoprecipitation assays, only the novel variant p.Arg247Ser showed diminished interaction with pVHL. A direct interaction between HIF-2α Arg247 and pVHL was confirmed in structural models. Transactivation was assessed by means of a HRE-containing reporter gene in transiently transfected cells, and significantly higher reporter activity was only observed with EPAS1/HIF-2α p.Phe374Tyr and p.Pro785Thr. In conclusion, three germline EPAS1 variants (c.739C>A (p.Arg247Ser), c.1121T>A (p.Phe374Tyr) and c.2353C>A (p.Pro785Thr)) all have some functional features in common with somatic activating mutations. Our findings suggest that these three germline variants are hypermorphic alleles that may act as modifiers to the expression of PPGLs.