Pertussis toxin induces parallel loss of neuropeptide Y Y1 receptor dimers and Gi α subunit function in CHO cells

Treatment with pertussis toxin in addition to a stable inhibition of Giα subunits of G-proteins also strongly reduced human neuropeptide Y Y1 receptors expressed in Chinese hamster ovary (CHO) cells. This was reflected in abolition of the inhibition by Y1 agonists of forskolin-stimulated adenylyl cyclase in intact cells, and of Y1 agonist stimulation of GTPγS binding to particulates from disrupted cells. The loss of both receptor and Giα subunit function was attenuated by ammonium chloride, an inhibitor of acid proteinases, pointing to a chaperoning co-protection of active pertussis toxin-sensitive Gα subunits and Y1 receptors. The surface complement of the Y1 receptor was changed a little in conditions of ∼ 85% decrease of the Y1 population, but the rate of the Y1 receptor-linked internalization of agonist peptides was reduced about 70%. The preserved receptor fraction consisted of monomers significantly coupled to Gqα subunits. The persistent pertussis toxin-insensitive internalization of agonists with the Y1 receptor may reflect a rescue or alternative switching that could be important for cell functioning in neuropeptide Y-rich environments. The results are compatible with a loss, due to Giα subunit inactivation by the toxin, of a large Y1 receptor reserve constituted of oligomers associating with heterotrimeric G-proteins.