Abstract
Luteinizing hormone receptors (LHR), expressed at physiological numbers <30,000 receptors per cell, translocate to and signal within membrane rafts following binding of human chorionic gonadotropin (hCG). Similarly LHR signal in cells when treated with bis(maltolato)oxovanadium(IV) (BMOV), bis(ethylmaltolato)oxovanadium(IV) (BEOV) or VOSO4, which decrease membrane lipid packing. Overexpressed LHR (>85,000 receptors per cell) are found in larger clusters in polarized homo-transfer fluorescence resonance energy transfer (homo-FRET) studies that were not affected by either hCG or vanadium compounds. Intracellular cyclic adenylate monophosphate (cAMP) levels indicate that only clustered LHR are active and produce the intracellular second messenger, cAMP. When LHR are over-expressed, cell signaling is unaffected by binding of hCG or vanadium compounds. To confirm the existence of intact complex, the EPR spectra of vanadium compounds in cell media were obtained using 1 mM BMOV, BEOV or VOSO4. These data were used to determine intact complex in a 10 μM solution and verified by speciation calculations. Effects of BMOV and BEOV samples were about two-fold greater than those of aqueous vanadium(IV) making it likely that intact vanadium complex are responsible for effects of LHR function. This represents a new mechanism for activation of a G protein-coupled receptor; perturbations in the lipid bilayer by vanadium compounds lead to aggregation and accumulation of physiological numbers of LHR in membrane raft domains where they initiate signal transduction and production of cAMP, a second messenger involved in signaling.
Luteinizing hormone receptors (LHR) accumulate in plasma membrane rafts upon binding of human chorionic gonadotropin (hCG) and initiate signal transduction. The action of hCG is mimicked by bis(maltolato)oxovanadium(IV) which interacts with membrane lipids, reduces lipid packing and, through a different mechanisms than hCG, causes LHR aggregation and signal transduction. [Display omitted]
•Luteinizing hormone receptors (LHR) accumulate in rafts following binding of human chorionic gonadotropin•LHRs in rafts initiate cell signaling•Bis(maltolato)oxovanadium(IV) interacts with membrane lipids and decreases lipid packing•Reduced lipid packing causes aggregation of LHRs in membrane microdomains where receptors signal.