We have been interested in elucidating the cell-specific transcriptional factors that regulate activation of the proenkephalin (PENK) gene in bovine adrenal medullary chromaffin (BAMC) cells and C-6 rat glioma cells. Previous studies indicate that PKC pathway regulates the expression of PENK in BAMC cells. In order to compare the cell-specific expression of this opioid peptide gene, we have used C-6 glioma cells as a model to compare differences in the cellular factors which are involved in the transcriptional regulation. The expression of proenkephalin (PENK) mRNA in C-6 rat glioma cells was stimulated by norepinephrine ( a beta-adrenergic agonist) and markedly enhanced by the addition of dexamethasone (a glucocorticoid agonist) to the culture medium, although no induction of glucocorticoid-response-element (GRE)-binding proteins was detectable. In contrast, the stimulation of PENK mRNA expression was not observed with a protein kinase C activator, 12-tetradecanoyl phorbol 13-acetate (TPA), which stimulated the expression of c-fos and c-jun mRNA and their proto- oncoproteins (c-Fos and c-Jun). In addition, an AP-1 activity was induced by TPA and an induction of a kappaB-like binding activity was found with TPA plus cycloheximide treated cells. Together, it suggests that activation of PENK gene in C-6 cells is mainly mediated through beta- adrenergic agonist-elicited cyclic AMP signal pathway, and induction of AP- 1 and kappaB-like binding activities appear not to participate in gene activation. Interestingly, the Western blot data showed no increase in intracellular levels of proenkephalin between control and treated cells. However, a marked increase in immunoreactivities for proenkephalin and its derivative, [Met5]enkephalin was detected in medium and a lesser elevation in cells from modulator-treated cell culture through the time-course. These results indicated that there was an association between an increase in PENK mRNA expression and an elevation of proenkephalins and, subsequently, the synthesized proenkephalins were released into the medium.

Agency
National Institute of Health (NIH)
Institute
National Institute of Environmental Health Sciences (NIEHS)
Type
Intramural Research (Z01)
Project #
1Z01ES090061-03
Application #
3841178
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
3
Fiscal Year
1992
Total Cost
Indirect Cost
City
State
Country
United States
Zip Code