The c-fos cyclic AMP-responsive element conveys constitutive expression to a tissue-specific promoter

The c-fos and cardiac α-actin promoters share homologous 5′ protein binding elements that are essential for serum-inducible and tissue-specific expression, respectively. Additional elements, auxiliary proteins or factor modifications, must distinguish the individual transcriptional responses of these two promoters. An element in the c-fos basal promoter that is normally responsible for transient stimulation of the fos gene in response to Ca²⁺ or cyclic AMP (CRE) may be able to modulate the expression of the upstream elements. We report here that this element, when inserted into the cardiac α-actin promoter, conveys constitutive expression to this otherwise highly restricted promoter. Additional data support the proposal that the CRE binding protein creates an alternative pathway whereby upstream regulatory elements in the cardiac α-actin promoter can activate transcription in a manner which circumvents the requirement for a tissue-specific environment.