STIMULATION OF CLONED HUMAN SEROTONIN 5-HT1D-BETA RECEPTOR-SITES IN STABLY TRANSFECTED C6 GLIAL-CELLS PROMOTES CELL-GROWTH

The involvement of serotonin 5-HT1D beta receptor sites was investigat ed in the growth of rat C6 glial cells permanently transfected with a gene encoding a human 5-HT1D beta receptor. The 5-HT receptor identity of control and transfected C6 glial/5-HT1D beta cells was determined by reverse transcription-polymerase chain reaction using primers speci fic for rat 5-HT1A, rat 5-HT1B, rat 5-HT1D alpha, human 5-HT1D beta, a nd rat 5-HT2A receptor genes. Constitutive mRNA for 5-HT2A receptors w as present in control and transfected C6 glial/5-HT1D beta cells, wher eas mRNA for 5-HT1D beta receptor sites was only present in the transf ected C6 glial/5-HT1D beta cell line, 5-HT inhibited forskolin-stimula ted cyclic AMP formation and promoted cell growth, in contrast to the absence of any measurable effect in pcDNA3 plasmid-transfected and non transfected C6 glial cells. The 5-HT effects could be mimicked by suma triptan (EC(50) = 44-76 nM) and were totally and partially blocked by methiothepin (IC50 = 9 nM) and GR 127,935 (2'-methyl-4'-(5-methyl[1,2, 4] oxadiazol-3-yl)-biphenyl-4-carboxylic acid [4-methoxy-3-(4-methylpi perazin-1-yl)phenyl] amide; IC50 = 97 pM}, respectively. No effect on cell growth was measured with the 5-HT2 receptor agonist DOl [1-(2,5-d imethoxy-4-iodophenyl)-2-aminopropane; 10 mu M], suggesting that 5-HT2 A receptors are not involved in the 5-HT-stimulated C6 glial/5-HT1D be ta cell growth. Dibutyryl-cyclic AMP (0.3 mM)-treated cultures did not show sumatriptan-promoted cell growth, indicating an inhibitory role for cyclic AMP in the cell growth mediated by 5-HT1D beta receptor sit es. In conclusion, 5-HT promotes cell proliferation in transfected C6 glial/5-HT1D beta cells by stimulation of 5-HT1D beta receptor sites. These receptor sites may be a new target to modulate the growth of tum or cells.