Coupling of the human Y2 receptor for neuropeptide Y and peptide YY to guanine nucleotide inhibitory proteins in permeabilized SMS-KAN cells.

Abstract

Using guanine nucleotides, pertussis toxin, and specific antisera against the COOH-terminals of the alpha-subunits of Gi1/2, Gi3, and G(o), the binding and biological response of the Y2 receptor (Y2R) for peptide YY (PYY) was probed in SMS-KAN neuroblastoma cells. The specific binding of radiolabeled PYY exhibited a single apparent dissociation constant, KD = 76 pM for intact cells and KD = 906 pM for permeabilized cells. However, other data suggested existence of multiple receptor affinity states. A shift in KD and a decrease in apparent number of binding sites (Bmax) was observed in permeabilized cells when incubated with guanine nucleotides. By contrast, in membrane preparations guanine nucleotides induced only a decrease in Bmax. In intact cells, agonist exposure inhibited the intracellular accumulation of forskolin-stimulated cyclic AMP by 80% (IC50 = 420 nM) compared with 94% inhibition (IC50 = 380 nM) in permeabilized cells. In permeabilized cells, preincubation with antisera against alpha i1/2 and alpha i3 blocked the functional response of PYY, with anti-alpha i3 being the most potent; whereas anti-alpha o failed to affect the cyclic AMP levels. These results suggest that permeabilized SMS-KAN cells serve as a good model system for analysis of Y2R binding kinetics and functional response and that the Y2R interacts directly with several different GiS (but not G(o)).