Genome-Wide and Locus Specific Alterations in CDC73/HRPT2-Mutated Parathyroid Tumors

Abstract

Mutations in the hyperparathyroidism type 2 (HRPT2/CDC73) gene and alterations in the parafibromin protein have been established in the majority of parathyroid carcinomas and in subsets of parathyroid adenomas. While it is known that CDC73-mutated parathyroid tumors display specific gene expression changes compared to CDC73 wild-type cases, the molecular cytogenetic profile in CDC73-mutated cases compared to unselected adenomas (with an expected very low frequency of CDC73 mutations) remains unknown. For this purpose, nine parathyroid tumors with established CDC73 gene inactivating mutations (three carcinomas, one atypical adenoma and five adenomas) were analyzed for copy number alterations and loss of heterozygosity using array-comparative genomic hybridization (a-CGH) and single nucleotide polymorphism (SNP) microarrays, respectively. Furthermore, CDC73 gene promoter methylation levels were assessed using bisulfite Pyrosequencing. The panel included seven tumors with single mutation and three with double mutations of the CDC73 gene. The carcinomas displayed copy number alterations in agreement with previous studies, whereas the CDC73-mutated adenomas did not display the same pattern of alterations at loci frequently deleted in unselected parathyroid tumors. Furthermore, gross losses of chromosomal material at 1p and 13 were significantly (p = 0.012) associated with parathyroid carcinomas as opposed to adenomas. Quantitative PCR-based copy number loss regarding CDC73 was observed in three adenomas, while all the carcinomas were diploid or showed copy number gain for CDC73 gene. Hypermethylation of the CDC73 gene promoter was not observed. Our data could suggest that CDC73-mutated parathyroid adenomas exhibit a partly unique cytogenetic profile in addition to that of carcinomas and unselected adenomas. Furthermore, CDC73-mutated carcinomas displayed losses at 1p and 13 which are not seen in CDC73-mutated adenomas, making these regions of interest for further studies regarding malignant properties in tumors from CDC73-mutated cases. However, due to the small sample size, validation of the results in a larger cohort is warranted.

Global and gene-specific promoter methylation analysis in primary hyperparathyroidism

“…In parathyroid tumors, a rare, homozygous activating β-catenin (CTNNB1) mutation has been demonstrated for a few cases, suggesting a role for β-catenin in parathyroid tumorigenesis. 36 Subsequent studies regarding β-catenin expression in parathyroid tumors revealed discordant findings regarding sub-cellular is in agreement with our own and others' previous reports, 15,16 further excluding promoter hypermethylation as an inactivation mechanism. In addition, the methylation profile of the MEN1 and CDC73 mutated cases did not reveal any statistically significant differences.…”

“…Although tumor representativity was not performed for these cases, previous DNA analyses from these samples using array-comparative genomic hybridization (a-CGH) visualized gross chromosomal alterations in agreement with previous publications regarding parathyroid carcinomas. 16 In addition, paraffin-embedded tissue specimens from metastatic cases have shown high tumor cell proportion in comparison to surrounding lung tissue, suggesting a high tumorto-normal tissue proportion. 51 In summary, this study suggests a role of aberrant promoter methylation for APC 1A, RASSF1A, and β-catenin genes in the molecular pathogenesis of a subset of parathyroid tumors and may indicate the disruption of multiple pathways.…”

“…52 The mutational status of both MEN1 and CDC73 genes were known for a number of the cases. 16,[51][52][53][54] Five cases had a MEN1 mutation (T57-T61) and 8 cases, including the 3 carcinomas, had a CDC73 mutation (T62-T66 and T70-T72). Apart from the three carcinomas which were obtained from the Tokyo Women's Medical University Hospital in Japan, all the other samples were retrieved from Karolinska University Hospital.…”

“…12,13 While one study has reported hypermethylation of CDC73 in a subset of parathyroid carcinomas, 14 more recent reports excluded epigenetic silencing of CDC73 gene in parathyroid tumors. 15,16 To further elucidate the role of DNA methylation in parathyroid tumors and as an extension to our previous study, 12 we have quantified the methylation density at the promoter of a number of plausible candidate genes, such as APC 1B, CASR, CDC73, MEN1, PAX1, SFRP1 and VDR, in addition to the previously analyzed genes, such as APC 1A, β-catenin (CTNNB1), P16 and RASSF1A, using a different and larger panel of parathyroid tumors. We also estimated the global methylation level by assessing LINE-1 methylation.…”

TERT promoter mutations are rare in parathyroid tumors

“…It has previously been reported in a pleomorphic xanthoastrocytoma (Koelsche et al 2013). The patient, a 16-year-old male with unknown family history of the disease and lost to follow-up, carries a constitutional W45X mutation of CDC73 together with a second W30X mutation of CDC73 in T1 (Sulaiman et al 2012).…”