Regulation of StAR mRNA expression. StAR mRNA expression is determined by the balance between transcription and mRNA turnover, each of which is regulated by multiple factors. Promoter elements and mRNA sequence elements are shown that are subject to regulation by physiological changes, such as hormonal stimulation (which increases cAMP levels) and cholesterol depletion (which activates SREBP). cAMP and oxidant-activated MAP kinases exert negative and positive effects respectively on mRNA stability, possibly via the StAR AU-rich element (AURE). StAR mRNA stability is also regulated by suppression of transcription or translation. Stabilization of an otherwise rapidly degraded mRNA is a regulatory mechanism that allows for extremely rapid and sensitive control of gene expression.