TYROSINE-HYDROXYLASE GENE PROMOTER ACTIVITY IS REGULATED BY BOTH CYCLIC AMP-RESPONSIVE ELEMENT AND AP1 SITES FOLLOWING CALCIUM INFLUX - EVIDENCE FOR CYCLIC AMP-RESPONSIVE ELEMENT-BINDING PROTEIN-INDEPENDENT REGULATION

Membrane depolarization of PC12 cells using 50 mM KCI leads to inducti on of tyrosine hydroxylase (TH) mRNA, This induction of TH mRNA is app arently due to increased TH gene promoter activity mediated by the inf lux of Ca2+. In PC12 cells transiently transfected with a chimeric gen e expressing chloramphenicol acetyltransferase (CAT) driven by the pro ximal TH gene 5'-flanking region, 50 mM KCl increases TH gene promoter activity 3-4-fold, Promoter analysis utilizing TH-CAT constructs cont aining mutagenized sequences indicates that this response to the depol arization-mediated influx of Ca2+ is primarily dependent on both the T H cAMP-responsive element (CRE) and TH activating protein-1 (AP1) site . Minimal promoter constructs that contain a single copy of either the TH CRE or TH AP1 site fused upstream of the TH gene basal promoter ar e only modestly responsive or nonresponsive, respectively, to depolari zation. However, both these constructs are strongly responsive to the calcium ionophore, A23187, Gel shift assays indicate that TH AP1 compl ex formation is dramatically increased after treatment with either 50 mM KCl or A23187. Using antibodies to transcription factors of the Fos and Jun families, we show that the nuclear proteins comprising the in ducible TH AP1 complex include c-Fos, c-Jun, JunB, and JunD. In cAMP-r esponsive element binding protein (CREB)-deficient cell lines that exp ress antisense RNA complementary to CREB mRNA, the response of the TH gene promoter to cyclic AMP is dramatically inhibited, but the respons e to A23187 remains robust, This result indicates that transcription f actors other than CREB can participate in the Ca2+-mediated regulation of the TH gene. In summary, our results support the hypothesis that r egulation of the TH gene by Ca2+ is mediated by mechanisms involving b oth the TH CRE and TH AP1 sites and that transcription factors other t han or in addition to CREB participate in this response.