The processing of receptor-bound [125I-Tyr11]somatostatin by RINm5F insulinoma cells.

摘要: The peptide somatostatin (SRIF) is secreted by delta cells of the endocrine pancreas and inhibits secretion insulin from pancreatic beta cells. We have previously shown that [125I-Tyr11]SRIF binds to specific, high affinity receptors on RINm5F insulinoma these mediate action SRIF inhibit release. In present study we investigated processing receptor-bound in this clonal cell line. Surface-bound internalized peptides were distinguished ability an acid/salt solution (0.2 M acetic acid, 0.5 NaCl, pH 2.5) dissociate only exposed ligand-receptor complexes. Surprisingly, greater than 80% saturably bound was removed acid wash independent time or temperature binding incubation. contrast, [125I]EGF (epidermal growth factor) markedly temperature-dependent. Although over 90% dissociated after a 4 degrees C incubation, less 10% treatment 37 binding. radioactivity released upon dissociation analyzed performance liquid chromatography consist mixture intact (40%) [125I]tyrosine (60%). However, neither rate nor its degradation affected NH4Cl, methylamine, leupeptin at concentrations which inhibited lysosomal [125I] EGF. Of 11 other protease inhibitors tested, metalloendoprotease inhibitor, phosphoramidon, substantially reduced [125I-Tyr11]SRIF. These data indicate that, unlike EGF, not rapidly degraded nonlysosomal process may involve metalloendoprotease.