Absence of exon 10 of the human luteinizing hormone (LH) receptor impairs LH, but not human chorionic gonadotropin action

The LH receptor (LHR) mediates the actions of LH and human chorionic gonadotropin (hCG). In vivo data showed that deletion of exon 10 does not affect hCG action, whereas LH action is impaired. To investigate the role of exon 10 in LH/hCG action in vitro we created stable COS-7 cells expressing the LHR with (wt) or without (-ex10) exon 10. Binding experiments showed that the affinities of LH and hCG to the LHR wt and -ex10 were similar. Stimulation of wt with hCG or LH resulted in increased cAMP. cAMP production was significantly impaired in -ex10 stimulated with LH. This response was not altered by pertussis toxin, excluding that Gi becomes activated in LHR -ex10. In desensitization experiments, intracellular cAMP of LHR wt and -ex10 declined to approximately 30%. No difference in intracellular cAMP was detected between LHR wt or -ex10 after recovery and restimulation with hCG or LH. These experiments show that impaired cAMP production of LHR -ex10 stimulated with LH is not due to anomalous receptor coupling or desensitization. We conclude that although exon 10 of the LHR plays no role in ligand binding, it is important for receptor activation by LH by a mechanism probably involving extracellular conformational changes.