Human retinoblastomas have binding sites for the COOH-terminal segment of human beta-endorphin

Two human retinoblastoma cell lines (Y79 and McA) were evaluated for the presence of binding sites for human beta-endorphin (beta h-EP). Using tritiated beta h-EP (3H-beta h-EP) and synthetic beta-EP analogues, it was possible to demonstrate binding sites for 3H-beta h-EP with an ED50 of 3.5 nM in Y79 cells and 8 nM in McA cells respectively. The non-opioid segment [beta h-EP-(6-31)] retained about 20% relative potency in Y79 and 40% in McA in displacing the tritiated hormone when compared with beta h-EP. Camel beta-EP had a relative potency of less than 1% and beta h-EP-(1-27) was inactive in both cells in doses as high as 4 microM. Taken together with previous reports on similar binding sites in human neuroblastoma and glioblastoma cell lines, it appears that cell lines of neural origin have binding sites for the COOH-terminal of human beta-EP.