CELL TO CELL TRANSFER OF HORMONE RECEPTORS

Abstract

Adenylate cyclase in intact celfecan be inactivated by N-ethylmaleimide or by heat without apparent damage to the coupled hormone receptor. Subsequently the receptor can be transferred to the adenylate cyclase of another type of cell, simply by fusing the two cell types with each other by Sendai virus. Coupling occurs in the fused cell membrane between the preexisting components and requires, at most a few minutes. Coupling is measured by hormonal activation of adenylate cyclase in cell ghosts prepared after fusion (Proc. Nat. Acad. Sci. 73, 4410, 1976). By this procedure the ß-adrenergic receptor in turkey erythrocytes has been transferred to the adenylate cyclase of mouse erythroleukemia cells (F cells) and also to the enzyme in Y-1 rat adrenal tumor cells. The experiments show that the hormone receptor can be dissociated in a functional state from its original, inactivated, adenylate cyclase system and that the receptor is compatible with the enzyme in a different cell. The apparent dissociation constants for epinephrine and norepinephrine, measured through adenylate cyclase activation, remained unchanged when the ß-adrenergic receptor was transferred to the foreign adenylate cyclase system. Thus the dissociation constant is an intrinsic property of the receptor which seems not to be much influenced by the other components of the membrane. Cyclic AMP levels in the intact fused cell have also been measured. Within 3 min after onset of fusion the newly transferred ß-adrenergic receptor was already able to cause an increase in intracellular cyclic AMP in response to hormone addition. A new hormone responsiveness can therefore indeed be conferred on intact cells. The ß-adrenergic receptor has also been transferred from C6 glioma cells to F cells and to Y-1 cells. A different receptor, specific for prostaglandin E1, has been successfully transferred from the F cells to Y-1 and C6 cells. Thus the wedding of hormone receptors to heterologous adenylate cyclase systems can be performed among cells of different species and differentiation characteristics. It is therefore suggested that the various hormone receptors which are coupled to adenylate cyclase are all of similar structure, differing mainly in the confined area which binds the specific hormone. The newly developed experimental approach of heterologous coupling could be used to analyze biological defective systems by transfer of the receptor or the enzyme to their counterparts in a normally functioning cell. Such studies in biochemical compatibility might be extended to study other multicomponent systems in biological membranes.