ABSTRACT
It was shown that beta-endorphin and the synthetic decapeptide SLTCLVKGFY that corresponds to the amino acid sequence 364-373 of the human IgG heavy chain (referred to as immunorphin) is able to stimulate growth of the human T-lymphoblastoid cell line Jurkat. The antagonist of opioid receptors naloxone did not inhibit the stimulating effect of the peptides. Studies on [(3)H]-immunorphin binding to Jurkat cell receptors have demonstrated that it binds with high affinity to naloxone-insensitive receptors (K(d) = 1.3 nM; n = 5.2 x 10(5)). Unlabeled beta-endorphin and the 6-10 fragment of immunorphin completely inhibited the labeled ligand specific binding to naloxone-insensitive receptors on T lymphocytes (K(i) = 1.4 x 10(-7) and 3.7 x 10(-5) M, respectively). Thus, beta-endorphin and immunorphin share the naloxone-insensitive receptors on human T-lymphoblastoid cell line Jurkat.
Subject(s)
Receptors, Opioid , beta-Endorphin , Humans , Jurkat Cells , Naloxone/pharmacology , Peptides , Receptors, Opioid/chemistry , beta-Endorphin/metabolismABSTRACT
The synthetic decapeptide Ser-Leu-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr (termed immunorphin) corresponding to the sequence 364-373 of the CH3 domain of human immunoglobulin G heavy chain and its synthetic fragment VKGFY were found to compete with 125I-labeled beta-endorphin for high-affinity naloxone-insensitive binding sites on membranes isolated from the rat brain cortex (K(i)=1.18+/-0.09 and 1.58+/-0.11 nM, respectively). The binding specificity study revealed that these binding sites were insensitive not only to naloxone but to [Met(5)]enkephalin and [Leu(5)]enkephalin as well. The K(d) values characterizing the specific binding of 125I-labeled immunorphin and its fragment Val-Lys-Gly-Phe-Tyr to these binding sites were determined to be 2.93+/-0.27 nM and 3.17+/-0.29 nM, respectively.
Subject(s)
Brain/metabolism , Naloxone/pharmacology , Oligopeptides/pharmacology , Peptide Fragments/pharmacology , beta-Endorphin/pharmacology , Amino Acid Sequence , Animals , Binding Sites , Binding, Competitive , Cell Membrane/metabolism , Dose-Response Relationship, Drug , Immunoglobulin Constant Regions , Immunoglobulin G/chemistry , Immunoglobulin gamma-Chains , Kinetics , Ligands , Molecular Sequence Data , Narcotic Antagonists/pharmacology , Oligopeptides/chemistry , Peptide Fragments/chemistry , Peptides/chemistry , Protein Binding , Protein Structure, Tertiary , Rats , beta-Endorphin/chemistryABSTRACT
The influence of beta-endorphin and immunorphin on human leukemic cell growth in vitro was studied. It was shown that both peptides increase the growth of T-lymphoblastoid cells in a dose-dependent manner. The effect of these peptides on the 3H-thymidine incorporation into T-lymphoblastoid cell line Jurkat was not reversed by the antagonist of opioid receptor naloxone. Interestingly, these peptides had no effect on B-lymphoblastoid and promyelocyte cell growth, however they enhance 3H-thymidine incorporation into myeloid cell lines.
