Human Follitropin Receptor Lipid Raft Residency is Mediated by its Caveolin Binding Motif

The follicle stimulating hormone (FSH) is a necessary hormone involved in reproductive pathways in both males and females. Previous work in our lab has shown that its receptor (FSHR) contains a caveolin binding motif (CBM) which we believe is responsible for localization of the receptor to lipid raft domains of the membrane and for proper receptor signaling. Mutations were introduced to this motif to provide a deeper understanding of this interaction and identify the importance of specific sites within the CBM in FSHR. Discontinuous sucrose gradients were used to separate lipid raft from non-lipid raft portions of the membrane and western blotting was used to visualize the localization of the FSHR within the gradient. We found that disruption of the CBM of FSHR resulted in altered localization of the receptor relative to the wild type FSHR. Receptors with mutations F497L, F481L, and F486L, as well as F497L, F481L, F486L, and F489L were found to localize only to non-raft portions of the membrane, while receptors with mutations F481L, F486L, and F489L were found in both lipid raft and non-raft portions of the membrane. From this we concluded that F479 may play a more significant role in lipid raft localization and signaling. These findings are consistent with previous research within the lab, which show higher levels of basal signaling in CBM mutants compared to the wild type. The results of this study suggest that the CBM is important in proper signaling of FSH, and that certain sites within the CBM may be more important in this interaction than others. These findings are important in understanding FSHR function which could lead to the development of novel treatments for infertility.