A Conserved Mechanism for Steroid Receptor Translocation to the Plasma Membrane

Abstract

Multiple steroid receptors (SR) have been proposed to localize to the plasma membrane. Some structural elements for membrane translocation of the estrogen receptor ␣ (ER␣) have been described, but the mechanisms relevant to other steroid receptors are entirely unknown. Here, we identify a highly conserved 9 amino acid motif in the ligand binding domains (E domains) of human/mouse ER␣ and ER␤, progesterone receptors A and B, and the androgen receptor. Mutation of the phenylalanine or tyrosine at position ؊2, cysteine at position 0, and hydrophobic isoleucine/leucine or leucine/leucine combinations at positions ؉5/6, relative to cysteine, significantly reduced membrane localization, MAP and PI 3-kinase activation, thymidine incorporation into DNA, and cell viability, stimulated by specific SR ligands. The localization sequence mediated palmitoylation of each SR, which facilitated caveolin-1 association, subsequent membrane localization, and steroid signaling. Palmitoylation within the E domain is therefore a crucial modification for membrane translocation and function of classical sex steroid receptors.

Non-genomic actions of androgens

“…Mutational analysis established that a 9 amino acid motif in the ligand-binding domain of the AR mediates membrane translocation via palmitoylation. Mutations of these amino acids significantly reduced membrane localization, MAPK and PI3 kinase activation [90].…”

Caveolin proteins and estrogen signaling in the brain

“…Although research has focused primarily on palmitoylation of ERα and its variants [64,[67][68][69], the same mechanism for caveolae association has been described for ERβ [64,70]. Specifically, palmitoylation of human ERα at cysteine 447 (mouse 451) is essential for receptor interaction with CAV1 and its subsequent localization to the plasma membrane.…”

“…In CHO cells, mutation of cysteine 447 to an alanine results in a loss of membrane ERα. In addition, the physical interaction between ERα and CAV1 is abolished, and membrane estrogen effects are eliminated [64,70]. It is through regulation of palmitoylation that estradiol appears to affect the interaction between ERα and CAV1.…”

“…It is through regulation of palmitoylation that estradiol appears to affect the interaction between ERα and CAV1. In particular, stimulation of HELA cells with estradiol reduces ERα binding to CAV1 with a corresponding reduction in membrane ERα [64,70]. It is significant to note that it is the palmitoylation of a single amino acid that regulates the trafficking of ERα, as this residue is well conserved across species.…”

Membrane androgen receptor activation in prostate and breast tumor cells: Molecular signaling and clinical impact

“…It is widely accepted that rapid responses to steroid hormones are mediated by at least two types of receptors: (I) a pool of classical steroid receptors associated with or tethered to the plasma membrane either via palmitoylation (12) or via docking in membrane microdomains such as lipid rafts and caveolae (reviewed in (13) and (II) a specific G-protein coupled receptor (GPCR) or a receptor in close association with a GPCR (14)(15)(16). In the case of estrogen and progesterone, specific GPCRs have been identified, namely GPR30 for estrogen (17,18) and mPR for progesterone (5), respectively.…”