Succinate dehydrogenase subunit B mutations modify human neuroblastoma cell metabolism and proliferation

Paragangliomas (PGLs) are rare neuroendocrine tumours. About 30-40 % of these tumours are mutated in one of the different susceptibility genes, including those encoding the different subunits of the succinate dehydrogenase, a complex involved both in the tricarboxylic acid cycle and in the oxygen transport chain. The aim of this work was to investigate whether SDHB mutations may account for alterations in cell metabolism and functions. Since human PGL cell lines are not available, we used the neuroblastoma cell line (SK-N-AS) stably transfected with the wild-type human SDHB or different SDHB-mutated constructs carrying some significant mutations found in our patients affected by PGLs. Similarly to succinate dehydrogenase (SDH)-mutated tumour cells, mutated SK-N-AS clones showed reduced SDH enzyme activity. All clones showed normal citrate synthase activity, reduced oxygen consumption and reduced carbonic anhydride production, thus demonstrating a decreased in mitochondrial metabolism. In two of the three mutated SK-N-AS, we also found an increase in HIF1α expression. Surprisingly and unexpectedly, in all the SDHB-mutated clones, we found a significant decrease in glucose uptake and in lactate culture medium concentration, suggesting also a decrease of cytosolic metabolism. Finally, we found that these energetic changes were associated to an increase in cell proliferation and migration. Overall, these data demonstrate that although SDHB mutations significantly downregulate both mitochondrial and cytoplasmic cellular metabolism, these mutations are associated to an upregulation of some cellular functions, such as growth rate and invasiveness.