The CRE consensus sequence in the synapsin I gene promoter region confers constitutive activation but no regulation by cAMP in neuroblastoma cells.
Synapsin I is implicated in the modulation of neurotransmitter release and in synaptogenesis and is regulated by phosphorylation. The rat and human synapsin I genes both carry CRE and TRE consensus sequences in their promoter regions. This suggested that protein kinase-mediated signal pathways might also regulate synapsin I activity at the level of gene expression and thus contribute, on a slower time scale, to synaptic plasticity. We have therefore investigated, in neuroblastoma cell lines, the effects of agents that activate protein kinases on synapsin I gene expression. Unexpectedly, treatment with forskolin/IBMX was not found to enhance synapsin I mRNA levels. Rather, it causes a decrease to approximately 50% within 1 day although several CRE-dependent control genes are strongly induced. The calcium ionophore, A23187, lowers synapsin I mRNA to approximately 75%, and the phorbol ester, TPA, is without effect. Transient expression of a CAT fusion gene under the control of the synapsin I promoter region is also inhibited by forskolin/IBMX, as well as by protein kinase A (PKA) overexpression, suggesting that the decrease of synapsin I mRNA in response to forskolin/IBMX is due to the inhibition of transcription. Mutation of the CRE consensus does not affect the response to PKA, but it reduces the constitutive activity of synapsin I promoter constructs down to 30-50%. Nuclease footprinting experiments demonstrate sequence-specific binding proteins from brain, liver and NS20Y cell nuclear extracts to the CRE consensus sequence of the rat synapsin I promoter.
Hoesche
C
C
Institut für Physiologische Chemie, Medizinische Fakultät, Ruhr-Universität Bochum, Germany.
Bartsch
P
P
Kilimann
M W
MW
D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000494:pharmacology; D016384:Consensus Sequence; D000242:Cyclic AMP / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics*; D008969:Molecular Sequence Data; D009447:Neuroblastoma / Q000235:genetics*; D009687:Nuclear Proteins / Q000378:metabolism; D010703:Phorbol Esters / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D016704:Synapsins / Q000235:genetics*; D014407:Tumor Cells, Cultured
D017362:Cyclic AMP Response Element-Binding Protein; D009687:Nuclear Proteins; D010703:Phorbol Esters; D012333:RNA, Messenger; D016704:Synapsins; D000242:Cyclic AMP; D002118:Calcium