n-acetyl-beta-endorphin and beta-endorphin-(1-27)

Cultured murine bone marrow macrophages specifically bound 125I-labeled beta-endorphin. Binding was displaceable by 100 times molar excess of full-length beta-endorphin but was insensitive to the opioid receptor antagonist, naloxone. Binding was inhibited by beta-endorphin's C-terminal tetrapeptide, lys-lys-gly-glu, but not by the truncated N-terminal 27 amino acid fragment, indicating that binding of beta-endorphin to this receptor is dependent on its C-terminus. Macrophages incubated for 24 h with 10(-8)-10(-5) M prostaglandin E2 showed a dose-dependent increase in beta-endorphin binding, implying receptor up-regulation. This was also observed in response to the phosphodiesterase inhibitor, isobutylmethylxanthine, indicating that regulation of these receptors may be mediated through a cAMP-dependent process. This is the first demonstration that beta-endorphin receptor expression can be positively regulated.

Topics: 1-Methyl-3-isobutylxanthine; Amino Acid Sequence; Animals; beta-Endorphin; Binding, Competitive; Bone Marrow Cells; Cells, Cultured; Dinoprostone; Macrophages; Mice; Mice, Inbred DBA; Molecular Sequence Data; Naloxone; Peptide Fragments; Protein Binding; Receptors, Opioid; Up-Regulation