Cell-specific glucocorticoid repression of calcitonin/calcitonin gene-related peptide transcription. Localization to an 18-base pair basal enhancer element.
We have investigated the mechanisms underlying cell-specific glucocorticoid repression of calcitonin/calcitonin gene-related peptide (CGRP) gene expression. Treatment with the synthetic glucocorticoid dexamethasone has been shown to decrease mRNA levels in the 44-2C thyroid C cell line. Nuclear run-on assays showed that dexamethasone repressed transcription 2-3-fold in 44-2C cells. In contrast, dexamethasone stimulated calcitonin/CGRP transcription 4-6-fold in the CA77 thyroid C cell line. Transient transfection assays were used to map repression of reporter gene activity in 44-2C cells to a neuroendocrine cell-specific enhancer located between -920 and -1125 base pairs (bp). Within this region, an 18-bp element was found that conferred both full basal enhancer activity and dexamethasone-dependent repression in 44-2C cells. The 18-bp region contains possible binding sites for AP-1 and helix-loop-helix transcription factors as well as a glucocorticoid receptor half-site. Colocalization of repression and enhancer activity was then investigated in other cell lines. In CA77 cells, while the 920-1125 region strongly enhanced transcription, the 18-bp region conferred only partial activation and dexamethasone had little effect on reporter gene activity. Dexamethasone did not repress the calcitonin/CGRP activity in the heterologous HeLa and Rat1 fibroblast cell lines. These results suggest that glucocorticoids repress transcription of the calcitonin/CGRP gene by inhibiting cell-specific transcription factor activity.
Tverberg
L A
LA
Department of Physiology and Biophysics, University of Iowa, Iowa City 52242.
Russo
A F
AF
D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D001665:Binding Sites; D002116:Calcitonin / Q000096:biosynthesis / Q000235:genetics*; D015740:Calcitonin Gene-Related Peptide / Q000096:biosynthesis / Q000235:genetics*; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*
D012333:RNA, Messenger; D014157:Transcription Factors; D003907:Dexamethasone; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide