KCl and forskolin synergistically up‐regulate cholecystokinin gene expression via coordinate activation of CREB and the co‐activator CBP

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Abstract
Cholecystokinin (CCK) is one of the most abundant peptide transmitters in the mammalian brain. Despite the physiological significance of CCK expression in long‐term memory and psychiatric disorders, little is known about the factors that regulate the expression of CCK peptides. Here, we report that KCl and forskolin synergistically increase CCK gene transcription via protein kinase A (PKA) and extracellular signal‐regulated kinase (ERK) signalling pathways, activating cAMP response element‐binding protein (CREB) associated with the CRE(− 80) element of the CCK promoter. Whereas, CREB Ser133 phosphorylation was essential for transcriptional activation, the synergistic stimulation was not correlated to the level of Ser133 phosphorylation, indicating that recruitment and/or activation of additional downstream factors were required for maximal stimulation. Transcriptional activation was reduced by co‐expression of adenovirus 12S E1A, that inhibits binding of CREB‐binding protein (CBP) to CREB. Moreover GAL4‐CREB‐DIEDML, which mediates the phosphorylation‐independent binding of CBP, and the C‐terminal domain of CBP was synergistically activated by forskolin and KCl. Taken together the results imply that neuronal CCK gene transcription is regulated by the cumulative action of calcium and cAMP via stimulation of the PKA and ERK signalling pathways and that synergy is accomplished by the coordinate activation of CREB and CBP.