Figure 4.

Cross-attenuation between hLHR and hFSHR heterodimers. Panel A, HEK293 cells stably transfected with empty vector (EV) (filled squares, solid lines) or hFSHR (open squares, dashed lines) were transiently transfected with hLHR under conditions in which cell surface hLHR levels in the 2 cell lines were closely matched and were approximately 10-fold less than cell surface hFSHR. In the experiment shown, hFSHR stably transfected cells bound 15.3 ng ¹²⁵I-hFSH/10⁶ cells and hFSHR and EV cells transfected with hLHR bound 1.63 and 1.66 ng ¹²⁵I-hCG /10⁶ cells, respectively. Cells were incubated with the indicated concentrations of hCG and cAMP levels were determined. B, HEK293 cells stably transfected with empty vector (EV) (filled squares, solid line) or hLHR (open squares, dashed line) were transiently transfected with hFSHR under conditions in which cell surface hFSHR levels in the 2 cell lines were closely matched and were approximately 10-fold less than cell surface hLHR. In the experiment shown, hLHR stably transfected cells bound 23.0 ng ¹²⁵I-hCG/10⁶ cells and hLHR or EV cells transfected with hFSHR bound 2.72 and 2.73 ng ¹²⁵I-hFSH/10⁶ cells, respectively. Cells were incubated with the indicated concentrations of hFSHR and cAMP levels were determined. C, HEK293 cells were stably transfected with empty vector (EV) (filled squares, solid line) or hLHR (open squares, dashed line) were transiently transfected with a low concentration of HA-hMC3R. The relative cell surface levels of MC3R in the EV cells and hFSHR cells as determined by flow cytometry were 673 and 798 relative light units, respectively. Cells were incubated with the indicated concentrations of NDP-MSH and cAMP levels were determined. For all panels, data shown are the mean ± SEM of triplicate determinations from one experiment representative of at least 3 independent experiments.