Proenkephalin gene expression in the PC12 pheochromocytoma cell line: stimulation by sodium butyrate

The differentiation promoter sodium butyrate increases the content of Met5-enkephalin-Arg6-Gly7-Leu8 (Met5-enk-RGL)-immunoreactive peptides in PC12 pheochromocytoma cells, which, unlike mature adrenomedullary chromaffin cells, contain exceedingly low levels of opioid peptides. These butyrate-induced enkephalin-immunoreactive peptides, which are specific products of the proenkephalin gene, consist principally of two high mol wt forms of amino-terminally extended Met5-enk-RGL. These high mol wt peptides, with apparent mol wt of 20,000 and 10,000, are approximately the same size as the two major immunoreactive peptides found in adult New England Deaconess Hospital rat adrenal. The low mol wt Met5-enk-RGL-immunoreactive peptide found in butyrate-treated cells is similar in size to authentic Met5-enk-RGL, which is not found in the adrenal medulla of the adult rat. When PC12 cells are grown as a tumor in vivo, the amount of Met5-enk-RGL-immunoreactive peptide increased only slightly above the level found in control cells grown in vitro and consisted exclusively of the highest mol wt immunoreactive species. In PC12 cells, the butyrate-stimulated elevation in the content of Met5-enk-RGL-immunoreactive peptides may involve changes in transcription, since the peptide increase is preceded by a 2- to 3-fold increase in the level of proenkephalin mRNA. These results suggest that the PC12 cell line may be useful for investigating those factors that control the initial expression and processing of proenkephalin-derived peptides during embryogenesis.