Beta-endorphin stimulates proliferation of small cell lung carcinoma cells in vitro via nonopioid binding sites

The small cell lung carcinoma cell line U-1690 bound beta-endorphin via nonopioid binding sites also recognized by the C-terminal part of this opioid peptide Lys-Lys-Gly-Glu, but not by opiate alkaloids such as naloxone and morphine or other opioid peptides. The beta-endorphin binding did not affect the production of cAMP, but was enhanced by dexamethasone pretreatment. The beta-endorphin-stimulated proliferation of U-1690 cells was inhibited by Lys-Lys-Gly-Glu and increased by dexamethasone pretreatment. The cells also produce beta-endorphin, suggesting an autocrine mechanism.