Chapter 21: Vanadium Compounds as Indirect Activators of a G Protein-coupled Receptor

A new mechanism for activation of luteinizing hormone receptors (LHR), a G-protein-coupled receptor, demonstrates that vanadium compounds can initiate receptor-mediated intracellular signaling via indirect effects on membrane lipids. BMOV and VOSO₄ decrease lipid packing, increase aggregation of LHR and initiation of LHR signaling. To determine whether LHR aggregation requires the continued presence of either BMOV or VOSO₄ in the cell membrane, we pretreated CHO cells with 10 µM BMOV or VOSO₄, washed cells to remove V-compounds and monitored lipid packing and receptor aggregation for 24 h. For cells with 10 000 LHR, pretreatment of cells with either BMOV or VOSO₄ decreased lipid packing and increased aggregation of LHR. The extent of receptor aggregation and lipid packing returned to baseline values over 24 h upon removal of V-compounds. When cells expressed 560 000 LHR per cell, receptors were already extensively aggregated and neither BMOV or VOSO₄ had a further effect on receptor aggregation despite reduced lipid packing. Thus, recovery from decreased lipid packing and, in cells where LHR density is low, increased receptor aggregation is slow. The effects of on membrane lipid order and the implications of this work for BMOV or VOSO₄ internalization are also discussed.