Processing of receptor-bound (125I-Tyr11)somatostatin by RINm5F insulinoma cells
The peptide somatostatin (SRIF) is secreted by delta cells of the endocrine pancreas and inhibits the secretion of insulin from pancreatic beta cells. It has been shown that (125I-Tyr11)SRIF binds to specific, high affinity receptors on RINm5F insulinoma cells and that these receptors mediate the action of SRIF to inhibit insulin release. In the present study we investigated the processing of receptor-bound (125I-Tyr11)SRIF in this clonal cell line. Surface-bound and internalized peptides were distinguished by the ability of an acid/salt solution (0.2 M acetic acid, 0.5 M NaCl, pH 2.5) to dissociate only exposed ligand-receptor complexes. Surprisingly, greater than 80% of saturably bound (125I-Tyr11)SRIF was removed by this acid wash independent of the time or temperature of the binding incubation. In contrast, the processing of receptor-bound (125I)EGF (epidermal growth factor) in RINm5F cells was markedly temperature-dependent. Although over 90% of saturably bound (125I)EGF was dissociated by acid after a 4 degrees C binding incubation, less than 10% was removed by acid treatment after 37 degrees C binding. The radioactivity released upon dissociation of receptor-bound (125I-Tyr11)SRIF was analyzed by high performance liquid chromatography and shown to consist of a mixture of intact peptide (40%) and (125I)tyrosine (60%). However, neither the rate of (125I-Tyr11)SRIF dissociation nor its degradation were affected by NH4Cl, methylamine, or leupeptin at concentrations which inhibited the lysosomal degradation of (125I) EGF. Of 11 other protease inhibitors tested, only the metalloendoprotease inhibitor, phosphoramidon, substantially reduced the degradation of receptor-bound (125I-Tyr11)SRIF. These data indicate that, unlike (125I) EGF, receptor-bound (125I-Tyr11)SRIF is not rapidly internalized by RINm5F cells and is degraded by a nonlysosomal process which may involve a metalloendoprotease.
- Research Organization:
- Harvard School of Public Health, Boston, MA
- OSTI ID:
- 5531967
- Journal Information:
- J. Biol. Chem.; (United States), Vol. 8
- Country of Publication:
- United States
- Language:
- English
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INSULIN
SECRETION
SOMATOSTATIN
BIOCHEMISTRY
CELL CULTURES
INHIBITION
IODINE 125
LABELLED COMPOUNDS
LYSOSOMES
PANCREAS
RATS
RECEPTORS
TRACER TECHNIQUES
ANIMALS
BETA DECAY RADIOISOTOPES
BODY
CELL CONSTITUENTS
CHEMISTRY
DAYS LIVING RADIOISOTOPES
DIGESTIVE SYSTEM
ELECTRON CAPTURE RADIOISOTOPES
ENDOCRINE GLANDS
GLANDS
HORMONES
INTERMEDIATE MASS NUCLEI
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
MAMMALS
MEMBRANE PROTEINS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANOIDS
ORGANS
PEPTIDE HORMONES
PROTEINS
RADIOISOTOPES
RODENTS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques