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Identification, characterization, and biological activity of somatostatin receptors in human neuroblastoma cell lines
Abstract:
To investigate the presence of biologically active somatostatin (SS) receptors in neural crest-derived tumors, radioligand binding studies, cyclic AMP accumulation, intracellular calcium, and growth assays were performed in eight human neuroblastoma (NB) cell lines. Mathematical modeling of binding experiments strongly indicates the presence of heterogeneity of sites. The first site (SSR1) is present in 40% of the NB cell lines and binds with low capacity (0.5 pmol/mg protein) and high affinity (0.1-1 nM) SS14, SS28, and analogues. The second site (SSR2) is a high capacity site (200 pmol/mg protein), widely distributed in all of the cell lines investigated, that shows relative selectivity yet low affinity (100 nM) for SS14, SS28, and [D-Trp8]SS14 without any apparent biological activity. SSR1 is coupled to a pertussis toxin-sensitive G protein, inhibits forskolin- or VIP-stimulated adenylate cyclase activity, decreases intracellular free calcium, and mediates inhibition (30%) of both DNA synthesis and cell growth. Analysis of cell cycle distribution in aphidicolin-synchronized SSR1-positive NB cells indicated that this inhibitory effect is partially mediated by a transient accumulation in G0-G1. Our data indicate high affinity binding sites for SS14, and analogues are present and biologically active in a subset of NB cells.
Insights
Biologically active somatostatin (SS) receptors were found in human neuroblastoma (NB) cells. High-affinity SS receptors (SSR1) inhibit cell growth and DNA synthesis in a subset of NB cell lines.
Area of Science:
- Neuroscience
- Endocrinology
- Oncology
Background:
- Neuroblastoma (NB) is a neural crest-derived tumor.
- Somatostatin (SS) receptors are implicated in various cellular functions.
- The presence and activity of SS receptors in NB are not fully understood.
Purpose of the Study:
- To investigate the presence and biological activity of somatostatin receptors in human neuroblastoma cell lines.
- To characterize the binding properties and signaling pathways of these receptors.
- To determine the impact of SS receptor activation on neuroblastoma cell growth.
Main Methods:
- Radioligand binding studies were performed on eight human NB cell lines.
- Assays for cyclic AMP accumulation, intracellular calcium levels, and cell growth were conducted.
- Mathematical modeling was used to analyze binding data and characterize receptor heterogeneity.
- Cell cycle analysis was performed on synchronized NB cells.
Main Results:
- Two distinct somatostatin receptor sites (SSR1 and SSR2) were identified, indicating receptor heterogeneity.
- SSR1, present in 40% of NB cell lines, exhibits high affinity for SS ligands and is coupled to a pertussis toxin-sensitive G protein.
- SSR1 activation inhibits adenylate cyclase, decreases intracellular calcium, and reduces DNA synthesis and cell growth by approximately 30%.
- SSR2 is a high-capacity, low-affinity site with no apparent biological activity.
Conclusions:
- Biologically active, high-affinity somatostatin receptors (SSR1) are present in a subset of human neuroblastoma cells.
- These SSR1 receptors can inhibit neuroblastoma cell proliferation and DNA synthesis, partly via G0-G1 cell cycle arrest.
- The findings suggest a potential therapeutic role for somatostatin analogues in treating neuroblastoma.