Functional expression or recombinant human luteinizing hormone/human choriogonadotropin receptor

The functional capacity of the recombinant human LH/hCG receptor was tested on the basis of gonadotropin stimulation of cAMP production by stable transfections of Chinese hamster ovary (CHO) cells. A CHO cell line expressed with the hLH/hCG receptor cDNA covering the entire amino acid coding region revealed the presence of LH/hCG binding site (Kd: 1.45 x 10(-10)M) on the plasma membrane. Treatment of transfected cells(CHO-LH/hCGR) with hCG induced dose-dependent increases in intracellular cAMP production, indicating that the expressed human LH/hCG receptor functionally couples with endogenous adenylyl cyclase. Although hCG induced dose-dependent increases in cAMP production, rat and bovine LH and human FSH did not alter cAMP levels compared to control values. Northern blot analysis with a cRNA probe derived from human LH/hCG receptor cDNA indicated the presence of three LH/hCG receptor mRNA transcripts(5.4, 3.6 and 2.4 kilobases) in RNA prepared from human ovary. Preincubation of CHO-LH/hCGR cells with hCG for 16h decreased the subsequent cAMP production caused by a 30min pulse of hCG stimulation. These results indicate that desensitization of the adenylyl cyclase response to hCG stimulation occurs in CHO-LH/hCGR cells. Therefore, this cell line provides a tool with which to pursue detailed studies on the molecular basis of LH/hCG induced desensitization.