Genotype and Tumor Locus Determine Expression Profile of Pseudohypoxic Pheochromocytomas and Paragangliomas

Abstract

Pheochromocytomas (PHEOs) and paragangliomas (PGLs) related to mutations in the mitochondrial succinate dehydrogenase (SDH) subunits A, B, C, and D, SDH complex assembly factor 2, and the von Hippel-Lindau (VHL) genes share a pseudohypoxic expression profile. However, genotype-specific differences in expression have been emerging. Development of effective new therapies for distinctive manifestations, e.g., a high rate of malignancy in SDHB- or predisposition to multifocal PGLs in SDHD patients, mandates improved stratification. To identify mutation/location-related characteristics among pseudohypoxic PHEOs/PGLs, we used comprehensive microarray profiling (SDHB: n = 18, SDHD-abdominal/thoracic (AT): n = 6, SDHD-head/neck (HN): n = 8, VHL: n = 13). To avoid location-specific bias, typical adrenal medulla genes were derived from matched normal medullas and cortices (n = 8) for data normalization. Unsupervised analysis identified two dominant clusters, separating SDHB and SDHD-AT PHEOs/PGLs (cluster A) from VHL PHEOs and SDHD-HN PGLs (cluster B). Supervised analysis yielded 6937 highly predictive genes (misclassification error rate of 0.175). Enrichment analysis revealed that energy metabolism and inflammation/fibrosis-related genes were most pronouncedly changed in clusters A and B, respectively. A minimum subset of 40 classifiers was validated by quantitative real-time polymerase chain reaction (quantitative real-time polymerase chain reaction vs. microarray: r = 0.87). Expression of several individual classifiers was identified as characteristic for VHL and SDHD-HN PHEOs and PGLs. In the present study, we show for the first time that SDHD-HN PGLs share more features with VHL PHEOs than with SDHD-AT PGLs. The presented data suggest novel subclassification of pseudohypoxic PHEOs/PGLs and implies cluster-specific pathogenic mechanisms and treatment strategies.

Update from the 4th Edition of the World Health Organization Classification of Head and Neck Tumours: Paragangliomas

“…A second susceptibility gene cluster with a greater predilection for pheochromocytomas and sympathoadrenal paragangliomas involves RET, RAS/MAPK/PI3K /mTOR pathways [3]. The two major clusters can be further divided according to phenotypes associated with individual genes [9,11]. Although some sporadic PGL or pheochromocytomas harbor somatic rather than germline mutations of hereditary susceptibility genes, germline mutations of these genes are much more common.…”

Hypoxia Pathway Mutations in Pheochromocytomas and Paragangliomas

“…As previously mentioned, PCC/PGL can be divided into 2 clusters: Cluster 1, which includes tumors characterized by the activation of a pseudohypoxia signaling pathway, and Cluster 2, which comprises tumors with activation of kinase signaling pathways, where pathogenic dysregulation of Ras and mTOR pathways occurs as a result of mutations in RET / NF1 / TMEM127 / MAX [Szabó et al, 2012;Shankavaram et al, 2013;Welander et al, 2014].…”

“…In addition, novel susceptibility genes have been associated with the development of these neuroendocrine tumors, including transmembrane protein 127 ( TMEM127 ), MYC associated factor X ( MAX ), fumarate hydratase ( FH ), kinesin family member 1B ( KIF1B ), Egl-9 family hypoxia-inducible factor 1/prolyl hydroxylase domaincontaining protein 2 ( EGLN1/PHD2 ) and, more recently, endothelial PAS domain protein 1/hypoxia-inducible factor 2-alpha ( EPAS1/HIF2A ) [Pinato et al, 2013;Shankavaram et al, 2013;Dahia, 2014;Welander et al, 2014].…”

“…As a result of multiple gene expression studies, some authors proposed the division of hereditary and sporadic PCC/PGL in 2 main clusters: Cluster 1 includes tumors with VHL and SDHx gene mutations, displaying a transcription profile characterized by the activation of a pseudohypoxia signaling pathway, whereas Cluster 2 comprises tumors with RET / NF1 / TMEM127 / MAX mutations, displaying a transcription profile characterized by the activation of kinase signaling pathways [Szabó et al, 2012;Shankavaram et al, 2013;Welander et al, 2014]. This review will focus on the pseudohypoxia-related Cluster 1 of PCC/PGL.…”

15 YEARS OF PARAGANGLIOMA: Genetics and mechanism of pheochromocytoma–paraganglioma syndromes characterized by germline SDHB and SDHD mutations

“…Recent genome-wide expression profiling studies show strong induction of hypoxia and angiogenesis pathways in SDH-and VHL-related PPGL (Dahia et al 2005, Lopez-Jimenez et al 2010, Shankavaram et al 2013. SDH and VHL mutations induce both protein encoding mRNAs and miRNAs (miR-210; Tsang et al 2014) that are implicated in cellular adaptation to hypoxia.…”