Down-regulation of calcitonin gene transcription by vitamin D requires two widely separated enhancer sequences

S. Peleg
1993 Molecular Endocrinology  
Transcription of the calcitonin (CT) gene is downregulated by vitamin D in normal and transformed thyroid C cells. DNA transfer techniques have been previously used to map and characterize a CAMPinduced enhancer at nucleotides -255 to -129 and an enhancer of basal transcription at -1000 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 -1480 to +90 were
more » ... 80 to +90 were attached to a promoterfess OH gene and transfected individually into the medullary thyroid carcinoma cell line TT. CT nucleotides -1480 to -129 induced significant basal transcription of the GH reporter gene in Tf cells. Basal transcription was elevated 3-fotd to 4-fold by treatment with CAMP analog. The biologically active metabofiie of vitamin DJ, 1,25dihydroxyvitamin DJ, had a minor (20%) inhibitory effect on basal transcription but inhibited more than 80% of the CAMP-induced transcrfptfon. We further investigated the CAMP-induced response and found that transcriptional activity of the downstream CAMP-induced enhancer was greatfy synergized in the presence of the upstream enhancer of basal tmnsorfption. The latter enhancer contained three functfonal CANNTG sequences designated El (nuclsotides -1080 to -1030), E2 (nucleotides -940 to -920), and E3 (nucleotfdes -920 to -900). E2 and E3 were essential for maximal CAMP-induced transcrfption. Detailed mapping of the vitamin D response showed that a minimum requirement for inhibMon of the CAMP-induced enhancer by vitamin D was a sequence overlapping E3 (nucfeotides -920 o888aoQps/osw-1008%03.00/0 MEmY Cqydght CD 1993 by The Endocrine Society to -829). We conclude that a negative response element to vitamin D is located between nu&otMes -920 and -829 in the CT 5' flanking DNA. It is Possible that vitamin D inhibits transoriptfon by interfering with the synergistic interaction between the CAMP-induced enhancer and the enhancer of basal transcription. (Molecular Endocrlndogy
doi:10.1210/me.7.8.999 pmid:8232320 fatcat:yd7c6s7khfddraf3xtz3msyq7y