SYNERGISTIC INDUCTION OF NEUROTENSIN GENE-TRANSCRIPTION IN PC12 CELLSPARALLELS CHANGES IN AP-1 ACTIVITY

A consensus AP-1 site in the promoter of the rat neurotensin/neuromedi n N (NT/N) gene is a critical regulatory element required for synergis tic regulation by combinations of nerve growth factor (NGF), lithium, glucocorticoids, and adenylate cyclase activators. A rapid RNase prote ction assay was developed to examine the kinetics of NT/N gene activat ion and to determine whether activation requires newly synthesized pro teins. Either NGF or lithium in combination with dexamethasone and for skolin transiently activated NT/N gene expression, but with distinct k inetics. Protein synthesis was not required for activation when NGF wa s used as the permissive inducer, but was required for the rapid down- regulation of the response. In contrast, lithium responses were attenu ated in the absence of protein synthesis, consistent with a requiremen t for newly synthesized AP-1 complexes in activation. In ail cases, in creases in NT/N gene expression closely paralleled increases in AP-1 b inding activity. Lithium in combination with other inducers caused del ayed increases in both AP-1 binding activity and c-jun, c-fos and fra- 1 gene expression. These results indicate that NGF and lithium exert t heir effects on NT/N gene expression through distinct pathways. The li thium pathway is active in neuronally-differentiated PC12 cells and co uld potentially be involved in the regulation of NT/N gene expression in the nervous system.