No abstract

The six major genes involved in hereditary susceptibility for pheochromocytoma (PCC)/paraganglioma (PGL) (RET, VHL, NF1, SDHB, SDHC, and SDHD) have been recently integrated into the same neuronal apoptotic pathway where mutations in any of these genes lead to cell death. In this model, prolyl hydroxylase 3 (EglN3) abrogation plays a pivotal role, but the molecular mechanisms underlying its inactivation are currently unknown. The aim of the study was to decipher specific alterations associated with the different genetic classes of PCCs/PGLs. With this purpose, 84 genetically characterized tumors were analyzed by means of transcriptional profiling. The analysis revealed a hypoxia-inducible factor (HIF)-related signature common to succinate dehydrogenase (SDH) and von Hippel-Lindau (VHL) tumors, that differentiated them from RET and neurofibromatosis type 1 cases. Both canonical HIF-1α and HIF-2α target genes were overexpressed in the SDH/VHL cluster, suggesting that a global HIF deregulation accounts for this common profile. Nevertheless, when we compared VHL tumors with SDHB cases, which often exhibit a malignant behavior, we found that HIF-1α target genes showed a predominant activation in the VHL PCCs. Expression data from 67 HIF target genes was sufficient to cluster SDHB and VHL tumors into two different groups, demonstrating different pseudo-hypoxic signatures. In addition, VHL-mutated tumors showed an unexpected overexpression of EglN3 mRNA that did not lead to significantly different EglN3 protein levels. These findings pave the way for more specific therapeutic approaches for malignant PCCs/PGLs management based on the patient's genetic alteration.

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are chromaffin-cell tumors that arise from the adrenal medulla and extra-adrenal paraganglia, respectively. The dysfunction of genes involved in the cellular response to hypoxia, such as VHL, EGL nine homolog 1, and the succinate dehydrogenase (SDH) genes, leads to a direct abrogation of hypoxia inducible factor (HIF) degradation, resulting in a pseudo-hypoxic state implicated in PCC/PGL development. Recently, somatic post-zygotic mutations in EPAS1 (HIF2A) have been found in patients with multiple PGLs and congenital erythrocytosis. We assessed 41 PCCs/PGLs for mutations in EPAS1 and herein describe the clinical, molecular and genetic characteristics of the 7 patients found to carry somatic EPAS1 mutations; 4 presented with multiple PGLs (3 of them also had congenital erythrocytosis), whereas 3 were single sporadic PCC/PGL cases. Gene expression analysis of EPAS1-mutated tumors revealed similar mRNA EPAS1 levels to those found in SDH-gene- and VHL-mutated cases and a significant up-regulation of two hypoxia-induced genes (PCSK6 and GNA14). Interestingly, single nucleotide polymorphism array analysis revealed an exclusive gain of chromosome 2p in three EPAS1-mutated tumors. Furthermore, multiplex-PCR screening for small rearrangements detected a specific EPAS1 gain in another EPAS1-mutated tumor and in three non-EPAS1-mutated cases. The finding that EPAS1 is involved in the sporadic presentation of the disease not only increases the percentage of PCCs/PGLs with known driver mutations, but also highlights the relevance of studying other hypoxia-related genes in apparently sporadic tumors. Finally, the detection of a specific copy number alteration affecting chromosome 2p in EPAS1-mutated tumors may guide the genetic diagnosis of patients with this disease.