Exclusive underexpression of vitamin D receptor exon 1f transcripts in tumors of primary hyperparathyroidism

Primary hyperparathyroidism (pHPT) is characterized by excessive production of parathyroid hormone (PTH) due to parathyroid adenomas while uremic secondary HPT (sHPT) is caused by parathyroid hyperplasia in response to renal failure. Active vitamin D, 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)), with the vitamin D receptor (VDR) is involved in regulation of the calcium homeostasis together with PTH. In a feedback loop, 1,25-(OH)(2)D(3) has a direct action on the parathyroid gland to regulate PTH transcription, PTH secretion and cell proliferation. We have previously demonstrated reduced VDR mRNA expression in parathyroid adenomas and hyperplasia of sHPT using a probe detecting all 14 variant VDR transcripts expressed in parathyroid cells. Here we have assessed which of the 5'-terminal exon 1a, 1d and 1f variant VDR transcripts are reduced in pathological parathyroid glands.