PT  - JOURNAL ARTICLE
AU  - Katharine Herrick-Davis
AU  - Ellinor Grinde
AU  - Tara Lindsley
AU  - Milt Teitler
AU  - Filippo Mancia
AU  - Ann Cowan
AU  - Jospeh E. Mazurkiewicz
TI  - Native Serotonin 5-HT2C Receptors are Expressed as Homodimers on the Apical Surface of Choroid Plexus Epithelial Cells.
AID  - 10.1124/mol.114.096636
DP  - 2015 Jan 01
TA  - Molecular Pharmacology
PG  - mol.114.096636
4099  - http://molpharm.aspetjournals.org/content/early/2015/01/21/mol.114.096636.short
4100  - http://molpharm.aspetjournals.org/content/early/2015/01/21/mol.114.096636.full
AB  - G protein-coupled receptors (GPCR) are a prominent class of plasma membrane proteins that regulate physiological responses to a wide variety of stimuli and therapeutic agents. While GPCR oligomerization has been studied extensively in recombinant cells, it remains uncertain whether native receptors expressed in their natural cellular environment are monomers, dimers or oligomers. The goal of this study was to determine the monomer/oligomer status of a native GPCR endogenously expressed in its natural cellular environment. Native 5-HT2C receptors in choroid plexus epithelial cells were evaluated using fluorescence correlation spectroscopy (FCS) with photon counting histogram (PCH). An anti-5HT2C fragment antigen binding protein was used to label native 5-HT2C receptors. A known monomeric receptor (CD-86) served as a control for decoding the oligomer status of native 5-HT2C receptors by molecular brightness analysis. FCS with PCH revealed molecular brightness values for native 5-HT2C receptors equivalent to the molecular brightness of a homodimer. 5-HT2C receptors displayed a diffusion coefficient of 5 x 10-9 cm2/s and were expressed at 32 receptors/um2 on the apical surface of choroid plexus epithelial cells. The functional significance and signaling capabilities of the homodimer were investigated in HEK293 cells using agonists that bind in a wash-resistant manner to one or both protomers of the homodimer. While agonist binding to one protomer resulted in G-protein activation, maximal stimulation required occupancy of both protomers. This study demonstrates, for the first time, the homodimeric structure of 5-HT2C receptors endogenously expressed in their native cellular environment and identifies the homodimer as a functional signaling unit.