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pubmed:abstractText |
The first step in the synthesis of all steroids is the cleavage of cholesterol side chain, catalyzed by an electron transport system located in mitochondria consisting of ferredoxin reductase, ferredoxin, and cytochrome P450scc. These proteins are present in adrenal, gonad, placenta, and some parts of the brain. In addition, ferredoxin and ferredoxin reductase are also found in the kidney and liver. Whereas ferredoxin reductase levels remain constant in the cell, ferredoxin and P450scc levels are stimulated by trophic hormones using cAMP as an intracellular messenger. The ferredoxin promoter is relatively simple, consisting of a TATA box and two Sp1-binding sites. This simple module is enough to direct cAMP-dependent transcription in a steroidogenic cell-specific fashion. The regulatory region for the P450scc gene is more complex, containing many protein binding sites for different regulation purposes. Its TATA box directs cAMP-dependent transcription in a cell-type-specific manner. A transcription factor, steroidogenic factor 1 (SF1), activates P450scc gene expression. The tissue-specific expression of the P450scc gene is probably accomplished through the interaction of SF1 with other protein factors located further upstream of the control region. SF1 may also be involved in the cAMP response. An upstream region binding to cAMP-Responsive Element Binding Protein CREB and AP1 can respond to cAMP for gene activation. These analyses of regulatory elements provide the structural architecture for transcriptional regulation of the ferredoxin and the CYP11A11 gene.
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