Estrogen receptor alpha-mediated silencing of caveolin gene expression in neuronal cells

Estrogen receptors (ER alpha/ER beta) are expressed in neuronal cells and exhibit a variety of activities in the central nervous system. ER activity is regulated in a ligand-dependent manner and by co-regulatory factors. Caveolin-1 is a recently identified co-activator of ER alpha mediating the ligand-independent activation of this steroid receptor. Here the influence of ERs on caveolin expression in human neuroblastoma SK-N-MC cells as well as in rodent brain was investigated. We found that ectopic expression of ER alpha in SK-N-MC cells (SK-ER alpha) leads to a ligand-independent transcriptional suppression of caveolin-1/-2 genes. This suppression is specifically mediated by ER alpha and not ER beta because ER beta counteracts the observed caveolin-silencing process. Interestingly, decreased caveolin expression in SK-ER alpha is accompanied by changes in the methylation pattern of caveolin promoters. The analysis of selected promoter regions of the human caveolin-1 gene showed that certain CpG dinucleotides were hypermethylated in SK-ER alpha cells, whereas the same sites were unmethylated in control, ER beta-, and ER alpha/beta co-expressing SK-N-MC cells. Inhibition of DNA methylation or histone deacetylation led to partial re-expression of caveolin-1/-2 genes in SK-ER alpha. In vivo analysis revealed a down-regulation of caveolin-1 expression after long term estrogen exposure in certain regions of the mouse brain. In conclusion, we have shown for the first time that ER alpha and not ER beta silences caveolin-1/-2 expression in an epigenetic fashion in neuronal cells. The observed mechanism of gene silencing by ER alpha may have implications for the transcriptional regulation of further ER alpha target genes.