FOS FAMILY MEMBERS SUCCESSIVELY OCCUPY THE TYROSINE-HYDROXYLASE GENE AP-1 SITE AFTER NERVE GROWTH-FACTOR OR EPIDERMAL GROWTH-FACTOR STIMULATION AND CAN REPRESS TRANSCRIPTION

Nerve growth factor induces the neuronal-like differentiation of PC12 cells, and epidermal growth factor promotes PC12 viability and is weakly mitogenic. Despite these differences, both growth factors induced indistinguishable patterns of transient delayed transcription of the tyrosine hydroxylase (TH) gene and the expression of proteins encoded by Fos gene family members. Thus, TH expression is sensitive to signaling pathways common to these two growth factors. We show that c-fos and fosB successively occupy an AP-1 site-like element of the TH promoter after nerve growth factor treatment. Furthermore, under conditions of transient transfection, Fos family proteins may synergize with c-jun to transrepress TH gene transcription through the TH-fat-specific element. We demonstrate that this site is also a major positive acting site for TH control. These results suggest a model in which the long term effect of c-fos family protein expression is to limit the expression of the TH gene. We consider the novel properties of this element in providing temporal and cell type-specific regulation of TH transcription.