Related Experiment Video
Updated: Jun 6, 2026

Detection of Ligand-activated G Protein-coupled Receptor Internalization by Confocal Microscopy
Published on: April 9, 2017
Expression and ligand binding of bombesin receptors in pulmonary and intestinal carcinoids
P Kuiper1, H W Verspaget, I Biemond
1Department of Gastroenterology and Hepatology, Leiden University Medical Center, Leiden, The Netherlands.
Introduction:
Carcinoids are mainly found in the gastrointestinal (65%) and bronchopulmonary tract (25%). These neuroendocrine tumors secrete a wide range of bioactive peptides, including gastrin releasing peptide and neuromedin B, the mammalian analogs of bombesin. The purpose of this study was to investigate the quantity and localization of bombesin receptors in gastrointestinal and pulmonary carcinoids, and to reveal whether bombesin-like peptides (BLP) and their receptors are of any value in distinguishing pulmonary carcinoids from carcinoids of intestinal origin.
Methods:
Carcinoid tumors with pulmonary (no.=9) or intestinal (no.=15) localizations were analyzed by immunohistochemistry, autoradiography, and radioimmunoassay, to examine the presence of bombesin receptor subtypes and determine BLP levels in these tumors.
Results:
All 3 bombesin receptor subtypes (GRPR, NMBR, and BRS-3) were present on pulmonary and intestinal carcinoids by immunohistochemistry. In pulmonary carcinoids, low receptor ligand binding densities together with high and low BLP levels were found. Intestinal carcinoids showed predominantly high receptor ligand binding densities in combination with low BLP levels.
Conclusions:
The expression of bombesin receptor subtypes is independent from the carcinoid tumor origin, and is therefore not recommended as a distinction marker, although carcinoids of pulmonary and intestinal origin possess different receptor binding affinities for bombesin and dissimilar BLP levels. The combined presence of bombesin and its receptors might suggest the presence of a paracrine or autocrine growth loop in carcinoids.
Related Concept Videos
Transducer Mechanism: Enzyme-Linked Receptors
Major types that are helpful drug targets include:
Ligand Binding Sites
Protein-ligand interactions are quite specific; even though numerous potential ligands surround a cellular protein at any given time, only a particular ligand can bind to that protein. Moreover, a ligand binds only to a dedicated area on the surface of the protein, known as the...
Mitogens and the Cell Cycle
Role of Ephrin-Eph Signalling in Intestinal Stem Cell Renewal
Signal Transduction: Overview
Typically, signal transduction involves three...
GPCRs Regulate Adenylyl Cylase Activity
Two...