Gonadotropin-releasing hormone receptor concentration differentially regulates intracellular signaling pathways in GGH3 cells.

Pituitary cell lines (GGH3) expressing the GnRH receptor (GnRHR) were used to investigate the effect of GnRHR concentration on the ability of a GnRH agonist to activate second messenger systems. Four different strategies were utilized to generate cells expressing functionally different concentrations of receptors: (1) transient transfection with different concentrations of wild type GnRHR into GH3 cells, (2) utilization of two cell lines derived from a common stably transfected line expressing high (4,209 +/- 535 receptors/cell) or low (1,031 +/- 36 receptors/cell) concentrations of GnRHR, (3) co-incubation of GGH3-1' cells with a GnRH agonist (Buserelin) and a GnRH antagonist to compete for binding sites, and (4) photo-affinity binding to GnRHR with a GnRH antagonist to change effective receptor concentration. A range of receptor concentrations (1,000-8,000 receptors/cell) were generated by these techniques. Inositol phosphate (IP) and cAMP accumulation were quantified to assess the effect of receptor concentration on receptor-effector coupling. Under all four paradigms, the efficacy and potency of Buserelin stimulated IP production was dependent on receptor concentration. In contrast, Buserelin stimulated cAMP release was relatively unchanged at varying concentrations of GnRHR. This suggests that the cellular concentration of GnRHR affects the induction of cell signaling pathways. These results demonstrate that a single ligand-receptor-complex can differentially activate second messenger systems and present a mechanism by which multiple physiological endpoints can be differentially regulated by a single hormone/receptor interaction.