FUNCTIONAL SEROTONIN-2B RECEPTORS ARE EXPRESSED BY A TERATOCARCINOMA-DERIVED CELL-LINE DURING SEROTONINERGIC DIFFERENTIATION

Among immortalized teratocarcinoma-derived cells, the clone 1C11 is a committed precursor of the neuronal lineage. On day 2 of its serotonin ergic differentiation, this clone expresses only one subtype of seroto nin [5-hydroxytryptamine (5-HT)] receptor, which is functionally coupl ed to phosphatidylinositol hydrolysis. The identity of these receptors was established by comparing their properties with those of 5-HT2B re ceptors expressed by LMTK(-) fibroblasts stably transfected with the r ecently cloned murine cDNA NP75 (LM5 cells). In both cell types, the a nalysis of (2,5-dimethoxy-4-[I-125]iodophenyl)-2-aminopropane HCl ([I- 125]DOI) binding revealed the presence of a single class of sites, the affinity of which was 1 order of magnitude lower than that reported f or 5-HT2B receptors. In 1C11 cells differentiated for 2 days, as well as in LM5 cells, DOI binding was decreased by nonhydrolyzable analogs of GTP, indicating that the 5-HT2B receptor is functionally coupled to a G protein. The DOI-induced increase of phosphoinositide hydrolysis, which was correlated with both GTPase activity and binding data, is m ediated by a G(q) protein. This work demonstrates that the 5-HT2B rece ptor is functionally expressed before complete serotoninergic differen tiation of 1C11 cells. The inducible 1C11 clone thus provides an in vi tro model to investigate the possible role of the 5-HT2B receptor in t he expression of the serotoninergic phenotype.