Regulation of synapsin I gene expression by the zinc finger transcription factor zif268/egr-1.

zif268/egr-1 is an immediate early response gene that is involved in regulation of growth and differentiation. Its mRNA encodes a sequence-specific transcriptional activator containing three zinc fingers that act as the DNA-binding domain. Although zif268/egr-1 is expressed in the nervous system during neuronal excitation, no target gene has yet been identified. Here we report that the zif268/egr-1 protein bound in vitro to two sites in the proximal regulatory region of the human synapsin I gene. The zif268/egr-1 protein was also shown to stimulate transcription from this control region in transactivation assays. Additionally, the presence of a putative neural-restrictive silencer element next to one of the zif268/egr-1-binding sites interfered with transactivation in a tissue-independent manner. An analysis of the temporal expression pattern of zif268/egr-1 and synapsin I during neuronal differentiation of P19 embryonal carcinoma cells revealed that zif268/egr-1 mRNA was induced on day 5 and synapsin I mRNA on day 8 after retinoic acid treatment. From this data we conclude that the synapsin I gene is a target of the zif268 transcription factor; however, intermediate factors may also be involved in the activation.