24-25-dihydroxyvitamin-d-3 and Thyroid-Neoplasms

Transcription of the calcitonin (CT) gene is down-regulated by vitamin D in normal and transformed thyroid C cells. DNA transfer techniques have been previously used to map and characterize a cAMP-induced enhancer at nucleotides -255 to -129 and an enhancer of basal transcription at -1060 to -905 in the CT 5' flanking DNA. The same methods were used to identify a negative response element for vitamin D. Deletion mutants of a genomic fragment of CT extending from nucleotides -1460 to +90 were attached to a promoterless GH gene and transfected individually into the medullary thyroid carcinoma cell line TT. CT nucleotides -1460 to -129 induced significant basal transcription of the GH reporter gene in TT cells. Basal transcription was elevated 3-fold to 4-fold by treatment with cAMP analog. The biologically active metabolite of vitamin D3, 1,25-dihydroxyvitamin D3, had a minor (20%) inhibitory effect on basal transcription but inhibited more than 60% of the cAMP-induced transcription. We further investigated the cAMP-induced response and found that transcriptional activity of the downstream cAMP-induced enhancer was greatly synergized in the presence of the upstream enhancer of basal transcription. The latter enhancer contained three functional CANNTG sequences designated E1 (nucleotides -1060 to -1030), E2 (nucleotides -940 to -920), and E3 (nucleotides -920 to -900). E2 and E3 were essential for maximal cAMP-induced transcription. Detailed mapping of the vitamin D response showed that a minimum requirement for inhibition of the cAMP-induced enhancer by vitamin D was a sequence overlapping E3 (nucleotides -920 to -829). We conclude that a negative response element to vitamin D is located between nucleotides -920 and -829 in the CT 5' flanking DNA. It is possible that vitamin D inhibits transcription by interfering with the synergistic interaction between the cAMP-induced enhancer and the enhancer of basal transcription.

Topics: 24,25-Dihydroxyvitamin D 3; Base Sequence; Calcitonin; Calcitriol; Carcinoma, Medullary; Cyclic AMP; Depression, Chemical; Enhancer Elements, Genetic; Gene Expression Regulation; Humans; Molecular Sequence Data; Receptors, Calcitriol; Recombinant Fusion Proteins; Thyroid Neoplasms; Transcription, Genetic; Tumor Cells, Cultured

We utilized the TT cell, a human C-cell line derived from a medullary thyroid carcinoma, to study the effects of 1,25-dihydroxyvitamin D3 on cell growth and expression of the calcitonin gene. The growth rate of cells treated for 8 days with 1,25-dihydroxyvitamin D3 did not differ significantly from control or 24,25-dihydroxyvitamin D3 treated cells. Total RNA was isolated, and calcitonin and calcitonin gene-related peptide (CGRP) levels were measured by hybridization. 1,25 D3 lowered calcitonin and CGRP mRNA levels in a time- and dose-dependent fashion; 24,25 D3 had no effect. Northern blots revealed a decrease in the mature mRNA as well as the common precursor forms, indicating a transcriptional effect of 1,25 D3.

Topics: 24,25-Dihydroxyvitamin D 3; Calcitonin; Calcitonin Gene-Related Peptide; Calcitriol; Carcinoma; Dihydroxycholecalciferols; Humans; Kinetics; Neuropeptides; Nucleic Acid Hybridization; RNA, Messenger; Thyroid Neoplasms; Tumor Cells, Cultured

We previously reported increased mean serum 1,25-dihydroxyvitamin D (1,25-(OH)2D) and increased trabecular bone remodelling in patients with medullary thyroid carcinoma (MCT) and hypercalcitoninaemia. In the present paper we report that serum 1,25-(OH)2D and trabecular bone remodelling decreased following surgical cure for MCT and hypercalcitoninaemia in 4 patients despite no detectable post-surgical hypoparathyroidism or hypothyroidism. The results obtained in the present small number of patients suggest that the altered vitamin D metabolism and trabecular bone remodelling in patients with MCT is caused by the hypercalcitoninaemia.

Topics: 24,25-Dihydroxyvitamin D 3; Adult; Aged; Bone and Bones; Calcitonin; Calcitriol; Carcinoma; Dihydroxycholecalciferols; Female; Humans; Male; Middle Aged; Parathyroid Hormone; Thyroid Hormones; Thyroid Neoplasms; Vitamin D