A phosphorylation cluster of five serine and threonine residues in the C-terminus of the follicle-stimulating hormone receptor is important for desensitization but not for β-Arrestin-mediated ERK activation

Classically, the FSH receptor (FSH-R) mediates its effects through coupling to guanine nucleotide-binding protein α S subunit (Gαs) and activation of the cAMP/protein kinase A (PKA) signaling pathway. β-Arrestins are rapidly recruited to the FSH-activated receptor and play key roles in its desensitization and internalization. Here, we show that the FSH-R expressed in HEK 293 cells activated ERK by two temporally distinct pathways dependent, respectively, on Gαs/PKA and β-arrestins. Gαs/PKA-dependent ERK activation was rapid, transient, and blocked by H89 (a PKA inhibitor), but it was insensitive to small interfering RNA-mediated depletion of β-arrestins. β-Arrestin-dependent ERK activation was slower but more sustained and was insensitive to H89. We identified five Ser/Thr residues in the C terminus of the receptor (638–644) as a major phosphorylation site. Mutation of these residues into Ala (5A FSH-R) significantly reduced the stability of FSH-induced β-arrestin 1 and 2 interaction when compared with th...