Transcriptional regulation of neuronal genes and its effect on neural functions: Cumulative mRNA expression of PACAP and BDNF genes controlled by calcium and cAMP signals in neurons

Although it is widely accepted that an activity-dependent gene transcription is induced by the calcium (Ca²⁺) signals in neurons, it is still unclear how the particular mRNA moieties are transiently accumulated in response to synaptic transmission that evokes multiple intracellular signals including Ca²⁺ and cAMP ones. Promoters of the brain-derived neurotrophic factor (BDNF) and the pituitary adenylate cyclase-ativating polypeptide (PACAP) can commonly be activated through the cAMP-responsive element (CRE), to which the CRE-binding protein (CREB) predominantly bound. The activation of BDNF gene promoter I and III (BDNF-PI and -PIII, respectively) was mediated not only by the CREB but also by the upstream stimulatory factor, whereas that of PACAP gene promoter (PACAP-P) was mediated by only one CRE located at around -200. The PACAP-P was synergistically enhanced by Ca ²⁺ and cAMP signals through the CRE, whereas the BDNF-PI did not show such a synergistic activation upon the stimulation with both signals. In addition, we found that the half-lives of PACAP and BDNF mRNA were prolonged by the Ca²⁺ influx into neurons but not that of Arc mRNA, indicating an activity-dependent stabilization of particular mRNA species in neurons. Thus, the activity-dependent gene expression is co-ordinately controlled by Ca ²⁺ and cAMP signals not only at the transcriptional level but also at the post-transcriptional level for the cumulative mRNA expression in neurons.