Mutations in Caveolin Binding Motif Alter Human Follicle Stimulating Hormone Receptor Signaling

Understanding the function of follicle-stimulating hormone (FSH), is a key to making strides in reproductive healthcare. FSH targets Sertoli cells in the testes which are responsible for promoting spermatogenesis, and studies of signal transduction from the human follicle-stimulating hormone receptor (hFSHR) are essential for understanding issues related to fertility and contraception. hFSHR is found in microdomains of the cell membrane called lipid rafts. Lipid rafts contain high levels of cholesterol and sphingolipids and frequently include the protein caveolin. hFSHR contains a caveolin binding motif (CBM) sequence which includes four aromatic amino acids (all phenylalanine in the case of hFSHR). To assess the importance of the CBM in hFSHR function, mutants were created by changing phenylalanine residues to leucine. CMB’s mutated sites at F479/481 (AB), F481/486 (BC), and F486/489 (CD) were tested to determine the effect of the mutations on activation of the p44/42 MAP kinase pathway. Previous studies from our lab using mutants of 3 (ABC and BCD) or 4 (ABCD) phenylalanines showed an increase in signaling compared to the wild type cells. However, mutating just the AB or CD sites resulted in decreased signaling compared to the wild type receptor. Future studies are aimed at understanding the difference in signaling of double mutants versus the more extensively mutated (triple or quadruple mutants) caveolin binding motifs and the effect of the double mutants on other signaling pathways such as the production of cAMP. These studies will allow for a greater understanding of the role of caveolin in hFSHR function and provide insights into the role of lipid rafts in regulation of reproduction.