Neuroblastoma × Glioma Hybrid Cells Synthesize Enkephalin-Like Opioid Peptides

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Abstract
Partially purified extracts from neuroblastoma × glioma hybrid cells 108CC15 inhibit, like opioids, the prostaglandin E1‐evoked formation of cyclic AMP in a dose‐dependent manner in the same hybrid cells. The inhibition is prevented by the opioid antagonist naloxone. In addition, the same extract competes with [3H]naloxone and [3H]Leu‐enkephalin for binding to opioid receptors of hybrid cell membranes and to a specific antiserum, respectively. The opioid activity in the extracts is destroyed by carboxypeptidase A and leucine aminopeptidase, but not by trypsin. Further purification of the extracts by HPLC, TLC, or high‐voltage paper electrophoresis reveals in each case two active fractions which behave like Met‐ and Leu‐enkephalin. The Metenkephalinlike, but not the Leuenkephalin‐like, fraction is inactivated by treatment with BrCN. Dimethylaminonaphtylsulfonyl (dansyl) derivatives of Met‐ and Leu‐enkephalin correspond to [3H]dansyl derivatives of Met‐ and Leu‐enkephalin‐like substances from hybrid cells. Three to four times as much Met‐ertkephalin‐like as Leu‐enkephalin‐like material is present in the extract. The overall concentration of opioid peptides in the hybrid cells varies between 0.03 and 1.0 pmol Leu‐enkephalin equivalents per mg protein. The amount of opioids in the hybrid cells is strongly dependent on the cell density. The findings suggest that neuroblastoma × glioma hybrid cells contain opioid peptides that are very similar, if not identical, to Met‐ and Leu‐enkephalin. Opioid activity can also be detected in other neuronal cell lines and even in glioma cells.