5 - Hydroxytryptamine 4 ( a ) Receptor Is Coupled to the G Subunit of Heterotrimeric G 13 Protein

Serotonin (5-hydroxytryptamine (5-HT)) is an important neurotransmitter that regulates multiple events in the central nervous system. Many of the 5-HT functions are mediated via G protein-coupled receptors that are coupled to multiple heterotrimeric G proteins, including Gs, Gi, and Gq subfamilies (Martin, G. R., Eglen, R. M., Hamblin, M. W., Hoyer, D., and Yocca, F. (1998) Trends Pharmacol. Sci. 19, 2–4). Here we show for the first time that the 5-hydroxytryptamine 4(a) receptor (5-HT4(a)) is coupled not only to heterotrimeric Gs but also to G13 protein, as assessed both by biochemical and functional assays. Using reconstitution of 5-HT4(a) receptor with different G proteins in Spodoptera frugiperda (Sf.9) cells, we have proved that agonist stimulation of receptor-induced guanosine 5 -(3-O-thio)triphosphate binding to G 13 protein. We then determined that expression of 5-HT4(a) receptor in mammalian cells induced constitutiveas well as agonist-promoted activation of a transcription factor, serum response element, through the activation of G 13 and RhoA. Finally, we have determined that expression of 5-HT4(a) receptor in neuroblastoma glioma NIE-115 cells cause RhoA-dependent neurite retraction and cell rounding under basal conditions and after agonist stimulation. These data suggest that by activating 5-HT4(a) receptorG13 pathway, serotonin plays a prominent role in regulating neuronal architecture in addition to its classical role in neurotransmission.