Activation of the gene transcription is apparently modulated by a variety of stimuli. Many of the key factors that control important biological processes are transcriptional regulatory proteins. We have been interested in elucidating the cell-specific transcription factors that dictate the activation of the proenkephalin (PENK) gene in a primary culture of bovine-adrenal medullary chromaffin cells as well as in C6 rat glioma cells. The distinct characteristics of the PENK gene activation between these two cell systems have been observed and are summarized as follows. The regulation of the bovine PENK transcription requires the novel protein synthesis and appears to be predominantly mediated via the protein kinase C pathway because the activation by TPA (a tumor promoter) outmatched that by other classes of modulators. In contrast, the activation of the rat PENK transcription is rather responsive to the activation of adrenergic receptors that are linked to the C-AMP system and is refractory to TPA. The stimulation via the C-AMP pathway is independent of de novo protein synthesis. Furthermore, the activation by adrenergic agonists is synergistically potentiated by the presence of glucocorticoid dexamethasone, although the GRE domain is not yet identified. To gain insight into the mechanisms underlying the transactivation, the PENK gene will be subcloned into a reporter gene containing the basic TATA box. Using transfection and in vitro transcription efficacy assays, we will be allowed to define the responsive elements and to conform to the cell specificities. In addition, these approaches will shed some light on the role of dexamethasone partaking in the gene activation. More importantly, transcription factors will be characterized in terms of their biochemical nature.
