Regulation of proenkephalin expression in cultured skin mesenchymal cells.

Proenkephalin, a classically defined opioid encoding gene, is transiently expressed in nondifferentiated mesodermal cells during organogenesis. We examined the hypothesis that this expression is associated with mesenchymal cell proliferation. For this purpose, we established a cell culture derived from fetal skin mesenchyme that specifically expresses proenkephalin mRNA in correlation with hypodermis development. These mesenchymal cells also produce and secrete significant amounts of proenkephalin-derived peptides. Using this model system, we observed a marked increase in proenkephalin mRNA expression in response to serum. This effect is time dependent and reaches peak levels during the G1/S transition. Similarly, 12-O-tetradecanoyl-phorbol-13-ester, whose biological actions have been shown to be mediated by the activity of protein kinase C (PKC), up-regulates proenkephalin expression. Desensitization of PKC by prolonged exposure of cells to 12-O-tetradecanoyl-phorbol-13-ester attenuates the serum induction of proenkephalin. The results presented in this report demonstrate that proenkephalin expression in mesenchymal cells is regulated by serum factors via mechanisms that involve PKC activity. A possible association between proenkephalin expression and cell proliferation is suggested.

Regulation of proenkephalin A messenger ribonucleic acid levels in normal B lymphocytes: specific inhibition by glucocorticoid hormones and superinduction by cycloheximide.

Proenkephalin A (PEA) encodes a group of small peptides known to function as neurotransmitters, neuromodulators, and neurohormones in the nervous and neuroendocrine systems. This gene has been shown to be expressed in lymphoid cells, supporting the concept of bidirectional communication between the immune system and the central nervous system. In the present study, we investigated the effect of steroids and the inhibition of protein and RNA syntheses on the regulation of PEA expression in normal rat B cells. The transient expression of PEA messenger (m) RNA levels occurring normally in B cells was markedly inhibited by the presence of either 50 nM prednisolone or dexamethasone, both of which are glucocorticoids; other steroids, such as testosterone or the steroid-inactive metabolite androsterone, were ineffective. In the presence of cycloheximide, a protein synthesis inhibitor, PEA mRNA was superinduced by a factor of 15-fold. Sorting by flow cytometry of cycloheximide-treated cells followed by in situ hybridization analysis revealed that the expression of PEA mRNA was exclusively confined to a small fraction of B cells. These results indicate that the mechanisms regulating PEA gene expression in B cells differ from those previously described in cells of the neuroendocrine and the nervous systems.