Loss of parafibromin expression in a subset of parathyroid adenomas

Abstract

Inactivation of the hyperparathyroidism-jaw tumour syndrome (HPT-JT) gene, HRPT2, was recently established as a genetic mechanism in the development of parathyroid tumours. Its encoded protein parafibromin has tumour-suppressor properties that play an important role in tumour development in the parathyroids, jaws and kidneys. Inactivating HRPT2 mutations are common in HPT-JT and parathyroid carcinomas, and have been described in a few cases of parathyroid adenomas with cystic features. In this study, 46 cases of cystic parathyroid adenomas previously investigated for HRPT2 mutations were characterized with regard to MEN1 gene mutations, cyclin D1 expression and parafibromin expression. In normal tissues and cell lines, parafibromin was ubiquitously expressed. Furthermore, parafibromin was detected as a dominating nuclear and a weaker cytoplasmic signal in transfected cell lines. In the three parathyroid tumours with inactivating HRPT2 mutations parafibromin expression was not detectable, and in one of two cases with aberrantly sized parafibromin the protein was delocalized. Both high and low cyclin D1 levels were found among HRPT2-mutated and -unmutated tumours, suggesting that these events are not mutually exclusive in parathyroid tumour development. The presented data suggest that in the majority of benign parathyroid tumours the expression of parafibromin remains unaltered, while the loss of parafibromin expression is strongly indicative of gene inactivation through mutation of the HRPT2 gene.

Parafibromin immunoreactivity: its use as an additional diagnostic marker for parathyroid tumor classification

“…The following positive controls were used: HeLa cells transfected with plasmid DNA containing full-length HRPT2 cDNA and two parathyroid carcinomas (T4 and T23) for western blot and immunohistochemistry (Juhlin et al 2006), four paraffin-embedded adenomas on the same slide for immunohistochemistry including one with a rim of normal parathyroid (control adenoma 1) and 21 sporadic adenomas (the majority with a normal rim) as normal reference for immunohistochemistry. For sub-cellular fractionation and western blot analysis, frozen samples of two cystic adenomas with or without HRPT2 gene mutation and parafibromin inactivation (corresponding to T20 and T23 in Juhlin et al 2006), one secondary HPT gland, and a regular adenoma (control adenoma 2) were used.…”

“…For sub-cellular fractionation and western blot analysis, frozen samples of two cystic adenomas with or without HRPT2 gene mutation and parafibromin inactivation (corresponding to T20 and T23 in Juhlin et al 2006), one secondary HPT gland, and a regular adenoma (control adenoma 2) were used. All samples were obtained with informed consent and local ethical approval.…”

“…By contrast, 98-100% of unselected sporadic adenomas stained completely positive (Tan et al 2004, Gill et al 2006. In a subset of cystic adenomas, loss of parafibromin has been associated with HRPT2 mutations (Juhlin et al 2006).…”

“…Inactivating HRPT2 mutations are frequently detected on the somatic and sometimes germ line levels in apparently sporadic parathyroid carcinoma (Howell et al 2003, Shattuck et al 2003, Cetani et al 2004, as opposed to a small minority of adenomas (Carpten et al 2002, Howell et al 2003, Krebs et al 2005, Bradley et al 2006, Juhlin et al 2006. In immunohistochemical studies of unequivocal and HPT-JT-related carcinomas, complete loss, or reduced nuclear immunoreactivity was found in the majority of cases.…”

HRPT2-related familial isolated hyperparathyroidism: could molecular studies direct the surgical approach?

“…Tan et al (21) demonstrated loss of parafi bromin nuclear immunoreactivity in 96% of parathyroid carcinomas and in eight of nine adenomas associated to HPT-JT syndrome. Furthermore, normal expression of parafi bromin has been demonstrated in the majority of the sporadic parathyroid adenomas so far studied (20)(21)(22).…”