Induction of differentiation increases Met5-enkephalin and Leu5-enkephalin content in NG108-15 hybrid cells: an immunocytochemical and biochemical analysis.

Regulation of cellular content of the endogenous opioid peptides Met5-enkephalin and Leu5-enkephalin was investigated in neuroblastoma X glioma hybrid cells NG108-15 grown in both serum-supplemented and serum-free defined media. Untreated cells and cells induced to differentiate were stained using anti-Met5-enkephalin and anti-Leu5-enkephalin with the peroxidase-antiperoxidase immunocytochemical technique at the light microscopic level. In untreated NG108-15 cells grown in serum-supplemented medium, intense enkephalin-like immunoreactivity was localized in cell bodies and short processes of a select population of cells. The volume fraction of stained untreated cells remained constant throughout the time period investigated. When cells were induced to differentiate with N6,O2'-dibutyryl adenosine 3':5'-cyclic monophosphate (dBcAMP) or 8-bromo cyclic adenosine monophosphate (1.0 mM) treatment for 5 days, staining was found throughout the cytoplasm of perikarya and the extensive processes which were expressed, and the volume fraction of stained cells increased over 2-fold. Receptor-mediated stimulation of adenylate cyclase by prostaglandin E1 (10 microM) for 5 days produced results similar to those with dBcAMP. Pure cultures of differentiated cells with intense staining were obtained by further treatment of cultures, grown in the presence or absence of dBcAMP, with arabinosylcytosine (araC). Untreated, dBcAMP-treated and araC-treated NG108-15 cells grown in defined medium expressed staining patterns and volume fractions of stained cells similar to those grown in serum-supplemented medium; sodium butyrate (1.0 mM), however, increased the volume fraction of stained cells grown in defined medium over 3-fold, whereas it had little effect on staining of cells grown with serum. The presence of both Met5- and Leu5-enkephalin-like activities in NG108-15 cells was confirmed in acid extracts of cells by radioreceptor assay after separation by reverse phase high pressure liquid chromatography. Induction of differentiation in NG108-15 cells by dBcAMP treatment increased the cellular concentration of both enkephalins to over 2 times the levels found in untreated cells. The biochemical analysis for Met5-enkephalin- and Leu5-enkephalin-like activity compared well with the immunocytochemical data indicating that the enkephalin content is correlated with the state of differentiation of NG108-15 cells.