The effect of depolarization on expression of the human proenkephalin gene is synergistic with cAMP and dependent upon a cAMP-inducible enhancer

Abstract

Membrane depolarization is a critical component of neural signaling; in recent years there also has been a great deal of evidence that membrane depolarization can regulate neural gene expression. Therefore, excitatory neurotransmission may be an important mechanism of neural plasticity. We have investigated the intracellular pathways and DNA regulatory elements through which membrane depolarization activates expression of the neural gene encoding human proenkephalin. In PC12 and C6-glioma cells, depolarization-induced expression of a transfected proenkephalin fusion gene was proportional to extracellular calcium concentration and was inhibited by verapamil. Activation of the gene by KCl-induced depolarization or the calcium ionophore A23187 was dependent upon and synergistic with cAMP in PC12 and C6-glioma cells, but neither depolarization nor treatment with A23187 affected cAMP levels. Trifluoperazine and W7 inhibited depolarization-induced gene expression but did not affect expression induced by the adenylyl cyclase activator forskolin. At the level of the DNA, depolarization- induced activation is conferred on the proenkephalin gene by a previously characterized cAMP-inducible enhancer. Multiple copies of a single component element of that enhancer, containing the CGTCA sequence motif characteristic of cAMP regulatory elements, can reconstitute the entire repertoire of responses to both cAMP and depolarization. These data suggest a model in which membrane depolarization activates gene expression through a calcium-dependent pathway, potentially involving calmodulin, and in which the transcriptional responses to both cAMP and calcium are transduced by the same DNA element.

Degradation of the inducible cAMP early repressor (ICER) by the ubiquitin–proteasome pathway

“…Interestingly, in both cardiocytes (Figure 1, middle panel) and GH3 cells (Figure 1, lower panel), depolarization did not increase the steady-state levels of the transcripts coding for ICER. Thus, in contrast with previous observations in which depolarization and cAMP stimulation had a concordant effect on the steady-state levels of several transcripts, including c-fos, proenkephalin and Kv1.5 [24][25][26], here we demonstrated a discordant response. cAMP induced the expression of ICER transcripts, whereas depolarization had no effect on the steadystate levels of ICER transcript.…”

“…Membrane depolarization can induce the transcription of immediate early genes, such as c-fos, and other genes, such as proenkephalin and Kv1.5 [24][25][26]. This induction is mediated by a Ca# + \calmodulin-dependent protein kinase, which phosphorylates CREB on the same residue as PKA [31], explaining the concordant transcriptional response of several genes to cAMP and depolarization.…”

Amphetamine and Dopamine-Induced Immediate Early Gene Expression in Striatal Neurons Depends on Postsynaptic NMDA Receptors and Calcium

“…Nonetheless, activation of the cyclic AMP pathway has been shown to be necessary and sufficient for induction of CREB-regulated genes in several transformed cell lines (Nguyen et al, 1990). Thus, it is somewhat puzzling that amphetamine-mediated induction of c-fos and zif 268 gene expression has been reported to be inhibited by NMDA receptor antagonists in vivo (Snyder-Keller, 1991;Ohno et al, 1994;Wang et al, 1994).…”

Nuclear protein phosphorylation and growth control

“…Ca2+ mediates gene induction in response to membrane depolarization of various neuronal cell lines and this inducibility has been mapped to CRE-like elements in different promoters (Sheng et al, 1988;Nguyen et al, 1990). In addition, rapid phosphorylation of CREB at has been demonstrated in response to membrane stimulation (Sheng et al, 1991) (Sheng et al, 1991;Dash et al, 1991).…”