FUNCTIONAL EXPRESSION OF THE RECOMBINANT HUMAN FSH RECEPTOR

The functional capacity of the recombinant human FSH (hFSH) receptor w as tested on the basis of gonadotrophin stimulation of cyclic AMP (cAM P) production by transient transfections of 293 cells and stable trans fections of Chinese hamster ovary (CHO) cells. A CHO cell line express ed with the hFSH receptor cDNA covering the entire amino acid coding r egion revealed the presence of FSH binding site (K-d 6.2 x 10(-10) M) on the plasma membrane. Treatment of transfected cells with hFSH induc ed dose-dependent increases in intracellular cAMP production. These re sults indicate that the hFSH receptor functionally couples with endoge nous adenylyl cyclase. Although rat FSH also induced dose-dependent in creases in cAMP production, bovine FSH was effective only at high dose s and human chorionic gonadotropin did not alter cAMP levels compared with control values. Northern blot analysis with a cRNA probe derived from hFSH receptor cDNA indicated the presence of two common FSH recep tor mRNA transcripts (2.4 and 4.1 kb) in RNA prepared from a human ova ry and transfected cell lines. Preincubation of CHO cells expressing a functional hFSH receptor (CHO-FSHR) with FSH for 16 h decreased the s ubsequent cAMP production resulting from a 30-min pulse of FSH stimula tion. These results indicate that desensitization of the adenylyl cycl ase response to FSH stimulation occurs in CHO-FSHR cells. This cell li ne therefore provides a tool with which to pursue detailed studies on the molecular basis of FSH-induced desensitization.