beta-Endorphin: characteristics of binding sites in a neuroblastoma--glioma hybrid cell

Preparation of [125I-Tyr27,Leu5]beta h-endorphin and its use for crosslinking of opioid binding sites in human striatum and NG108-15 neuroblastoma-glioma cells

A radioligand suitable for crosslinking studies to opioid receptors has been obtained by radioiodination and purification of the monoiodotyrosine-27 derivative of the synthetic human beta-endorphin (beta h-endorphin) analogue [5-leucine]beta h-endorphin. The derivative, [27-[125I]monoiodotyrosine,5-leucine]beta h-endorphin, was crosslinked to human striatal (caudate and putamen) and NG108-15 neuroblastoma-glioma cell membranes by using disuccinimidyl suberate. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing conditions revealed four specifically labeled bands at 68, 40, 30, and 25 kDa for both human caudate and putamen, whereas NG108-15 cell membranes gave specifically labeled bands at 92, 56, 38, and 23 kDa.

beta-Endorphin: characterization of binding sites specific for the human hormone in human glioblastoma SF126 cells

The established human glioblastoma cell line SF126 was found to bind tritiated human beta-endorphin (beta h-EP) in a saturable fashion. From displacement studies, the ED50 was estimated to be about 2.5 nM. The Kd was estimated as 1.9 X 10(-9) M and Scatchard analysis showed a biphasic pattern with a predominant low-affinity component. Binding reached a maximum at about 90 min at 22 degrees C and was instantaneously reversible. Tritiated [D-Ala2,D-Leu5]enkephalin and tritiated dihydromorphine did not bind to the cells. Sodium at a concentration of 150 mM decreased the specific binding by 80%. The interaction with the cellular binding site appeared to be mediated by the COOH-terminal segment of beta h-EP, as beta h-EP-(6-31) retained a high potency for displacing tritiated beta h-EP, and beta h-EP-(1-27) has no activity. Camel beta-EP was only about 1% as active as the human hormone.

Human beta-endorphin: specific binding in neuroblastoma N18TG2 cells

The mouse neuroblastoma N18TG2 has specific, saturable binding sites for human beta-endorphin (beta h-EP). The affinity and number of sites are 1.1 nM and 280,000 per cell, respectively, beta h-EP binding is not inhibited by [Leu]enkephalin or morphine at concentrations up to 0.1 mM; beta h-EP-(6--31) is a potent inhibitor of binding, and camel beta-EP is much less potent. The data suggest the importance of the nonenkephalin segment of the beta h-EP molecule for interaction with the binding site in N18TG2 cells.