Etablierung eines humanen Modellsystems zur funktionellen Analyse derSomatostatinrezeptoren Typ 1, Typ 3 und Typ 4 in der humanen Karzinoid-Zell-Linie LCC-18

Establishment of a human model system for the functional analysis of somatostatin receptor subtype 1, subtype 3 and subtype 4 in the human carzinoid cell line LCC-18 Introduction: Somatostatin (SST) and its receptors are to this day one of the most interesting regulatory mechanisms for the control of hormonal and neurotransmitter mediated effects in the body. Here SST modulates through its receptors (SSTR) inhibitory activity the secretory cells and imparts directly cytostatic or cytotoxic effects on a target cell. Much research currently focuses on this area. In the process of investigation of until today still unknown details of the intracellular signaltransduction pathways of the SSTR subtyps there were repeatedly heterologous cell systems established. The results of such systems can however, in our view, only be attached universal significance in limited extent. Objective: The objective of this work was the functional verification of a new homologous human cell system for further investigation of somatostatin and its receptor subtypes, which was implemented by the stable transfection of the cloned human SSTR subtypes into cells of the human, previously SSTR free neuroendocrine coloncarcinoma cell line LCC-18. Methods: After double stable transfection of the genetic information of the particular SSTR subtypes into the human cells there were binding studies with SST-14, SST-28 and a new SST-polydextran-ligand in competition to 125I-Tyr-SST-14 performed. The SSTR mediated effects on the intracellular cAMP of the ligands specified above and on the gene expression were analyzed. Results: Successfully with the SSTR subtypes 1, 3 and 4 stable transfected clones were identified and binding studies proved the existence of the corresponding receptors. The intracellular cAMP was after pre-stimulation using forskolin significantly reduced by the SSTR mediated effect of all three ligands and the though the Chromogranin A Promotor initiated gene expression was also reduced by SST-14. Conclusion: A homologous human cell system could be established with options in the further exploration of the receptor subtype-specific intracellular signaling, of new SSTR agonisten and antagonists, of the interaction between cell membrane associated receptors and in the establishment of new tumor models.