Jump to Main Content
Characterization of cisâacting elements in the promoter of the mouse metallothioneinâ3 gene: Activation of gene expression during neuronal differentiation of P19 embryonal carcinoma cells
- Faraonio, Raffaella, Moffatt, Pierre, LaRochelle, Olivier, Schipper, Hyman M., SâArnaud, RenÃ©, SÃ©guin, Carl
- European journal of biochemistry 2000 v.267 no.6 pp. 1743-1753
- Human polyomavirus 2, astrocytes, nuclear proteins, genes, chromatin, gel electrophoresis, promoter regions, epigenetics, reproductive system, methylation, gene activation, brain, gene expression, metal ions, transcription (genetics), mice, liver, carcinoma, metallothionein, retinoic acid, deoxyribonuclease I
- The metallothionein (MT)3 gene is expressed predominantly in the brain and the organs of the reproductive system, and fails to respond to metal ions in vivo. A CTG repeat was proposed to function as a potential repressor element in nonpermissive cells, and a sequence similar to the JC virus silencer element was found to function as a negative element in permissive primary astrocytes. The objective of this study was to characterize further the mechanisms governing cellâtype specific MTâ3 gene transcription. We searched for a suitable cell line expressing the MTâ3 gene to be used for determination of MTâ3 promoter tissue specificity, and showed that MTâ3 expression is activated during neuroectodermal differentiation of P19 cells induced by retinoic acid to levels similar to those found in whole brain. Deletion of the CTG repeat or of the JC virus silencer did not promote MTâ3 promoter activity in nonpermissive cells, or enhance expression in permissive cells. We identified MTâ3 promoter sequences interacting with liver and brain nuclear proteins, as assayed by DNaseâI footprinting analyses and electrophoretic mobility shift assay, and assessed the role of these sequences in the regulation of MTâ3 expression by cotransfection experiments. We generated stable transfectants in permissive C6 and nonpermissive NIHâ3T3 cells, and analysed the methylation status of the MTâ3 gene. These studies show that regulation of tissueâspecific MTâ3 gene expression does not appear to involve a repressor, and suggest that other mechanisms such as chromatin organization and epigenetic modifications could account for the absence of MTâ3 gene transcription in nonpermissive cells.