Oxygen regulates proliferation and phenotype in the RS0 SDH-deficient pheochromocytoma cell line

The RS0 cell line is a rat-derived pheochromocytoma line developed as a model to study pheochromocytoma/paraganglioma caused by hereditary mutations of the SDHB gene. Previous studies demonstrated that xenografts of the RS0 parent tumor replicate characteristics of their human counterparts, including loss of SDHB and upregulation of genes in hypoxia signaling pathways activated by EPAS1/HIF2A. Establishment of the cell line required a low O2 concentration, as cell proliferation was arrested in a traditional cell culture atmosphere of 20% O2. The present study profiled the effects of 20% versus 5% O2 and EPAS1/HIF2A inhibitors on the RS0 cell phenotype and tested how RS0 cells cultured under these influences compare to their parent xenografts and normal rat adrenal medulla. O2 concentration in cell cultures influences almost every aspect of the cells' biology, most obviously proliferation but also ultrastructure, transcriptome, metabolism and endocrine function. The cells most closely resemble their xenografts when maintained in a low O2 environment, but some differences between the cells in vivo and in vitro are not fully explained. Genes downregulated in high O2 are predominantly associated with the cell cycle, while those upregulated in low O2 include stemness and neuronal progenitor markers that may have contributed to the establishment of the cell line, as well as drug targets expressed in human pheochromocytoma/paraganglioma. Some effects of high O2 are mimicked by EPAS1/HIF2A inhibitors currently considered for treatment of metastatic Sdh-deficient PPGL, while others may be HIF-independent. The cytostatic effect of EPAS1/HIF2A inhibitors is reversible, suggesting possible limits to their usefulness as monotherapies.