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Novel action of transforming growth factor beta 1 in functioning human pancreatic carcinoid cells
J Ishizuka1, R D Beauchamp, K Sato
1Department of Surgery, University of Texas Medical Branch, Galveston 77555-0533.
Abstract:
We have shown recently that 5-HT is an autocrine growth stimulatory factor for a cell line (BON) that is derived from a human pancreatic carcinoid tumor. This action is mediated by a 5-HT receptor-linked decrease of cyclic adenosine monophosphate (AMP) production, but not mediated by a 5-HT receptor-linked stimulation of phosphatidylinositol hydrolysis. The BON cells also express transforming growth factor betas (TGF beta s) (1, 2, and 3) and release TGF beta into their medium. In this study, we examined the effects of TGF beta on the secretion of 5-HT, on signal transduction pathways involved in 5-HT secretion, and on growth of BON cells. TGF beta 1 inhibited basal and acetylcholine-stimulated release of 5-HT, but did not inhibit isobutylmethylxanthine-stimulated release of 5-HT. TGF beta 1 inhibited both basal and acetylcholine-stimulated hydrolysis of phosphatidylinositol in a dose dependent manner, but did not affect cyclic AMP production. TGF-beta 1 inhibited growth of BON cells in culture; this effect was reversed by exogenously administered 5-HT. Three different specific and saturable TGF beta 1 binding sites were identified; binding assays performed after mild acid wash (0.1% acetic acid, pH 2.5) conditions uncovered TGF beta receptors that were apparently occupied by endogenously produced TGF beta species. Affinity cross-linking assay showed that BON cells had three different TGF beta binding proteins. These results suggest that TGF beta 1 can inhibit growth of BON cells by altering secretory responses of 5-HT by means of receptor-mediated inhibition of phosphatidylinositol hydrolysis. We conclude that growth of BON cells is regulated, at least in part, by the opposing receptor-mediated autocrine actions of 5-HT and TGF beta.
Insights
Transforming growth factor beta (TGF beta) 1 inhibits human pancreatic carcinoid BON cell growth by reducing serotonin (5-HT) secretion and phosphatidylinositol hydrolysis. Exogenous 5-HT reverses this growth inhibition, indicating opposing autocrine signaling.
Area of Science:
- Endocrinology
- Cell Biology
- Cancer Research
Background:
- Serotonin (5-HT) acts as an autocrine growth factor for human pancreatic carcinoid BON cells, mediated by decreased cyclic adenosine monophosphate (cAMP).
- BON cells express and release transforming growth factor betas (TGF beta s), including TGF beta 1, 2, and 3.
Purpose of the Study:
- To investigate the effects of TGF beta on 5-HT secretion, related signal transduction pathways, and BON cell growth.
- To elucidate the role of TGF beta in the autocrine regulation of pancreatic carcinoid cell proliferation.
Main Methods:
- Assessing 5-HT release under basal, acetylcholine-stimulated, and isobutylmethylxanthine-stimulated conditions following TGF beta 1 treatment.
- Measuring phosphatidylinositol hydrolysis and cyclic AMP production.
- Evaluating the impact of TGF beta 1 on BON cell proliferation and the effect of exogenous 5-HT.
- Identifying TGF beta 1 binding sites and proteins using binding assays and affinity cross-linking.
Main Results:
- TGF beta 1 inhibited both basal and acetylcholine-stimulated 5-HT release, but not isobutylmethylxanthine-stimulated release.
- TGF beta 1 dose-dependently inhibited phosphatidylinositol hydrolysis but did not affect cAMP production.
- TGF beta 1 suppressed BON cell growth, an effect reversed by exogenous 5-HT.
- Three specific TGF beta 1 binding sites and three corresponding binding proteins were identified on BON cells.
Conclusions:
- TGF beta 1 inhibits pancreatic carcinoid BON cell growth via receptor-mediated inhibition of phosphatidylinositol hydrolysis, altering 5-HT secretion.
- BON cell growth is regulated by the opposing autocrine actions of serotonin and TGF beta.