Beta adrenergic receptors and adenylate cyclase: Products of separate genes

Wild type S49 mouse lymphoma cells produce adenosine 3',5' monophosphate when exposed to the beta adrenergic agonist isoproterenol; treatment with this agent in the presence of a phosphodiesterase inhibitor is cytocidal. Particulate preparations from such cells have adenylate cyclase activity and bind [ ¹²⁵I]iodohydroxybenzylpindolol, a potent beta adrenergic antagonist that can be used to examine beta adrenergic receptors. The binding of this ligand is rapid and reversible; Scatchard analysis gives results compatible with a single class of binding sites with a KDof 33 pM. Beta adrenergic agonists and antagonists compete for radioactive ligand binding sites stereoselectively and at concentrations that correlate closely with those required for activation or inhibition of activation of adenylate cyclase. A clone has been isolated from wild type cells that is resistant to isoproterenol induced cyclic AMP killing. This clone has no detectable adenylate cyclase activity in response to isoproterenol, prostaglandin E ₁, or sodium fluoride. Nevertheless, the characteristics of binding of [ ¹²⁵I]iodohydroxybenzylpindolol by this adenylate cyclase negative clone resemble those of wild type preparations. The similarity of binding by these two clones extends to the kinetics of binding, the affinity for ligand, and the potency of competitors for binding sites. Both clones have 200-300 receptor sites/cell. Another clonal cell line, HC 1 (a rat hepatoma), is phenotypically similar to the adenylate cyclase negative lymphoma cell; enzyme activity is not detectable, although binding activity characteristic of the beta adrenergic receptor is present. The existence of beta adrenergic receptor activity in cells that appear to lack adenylate cyclase suggests that the beta adrenergic recognition (receptor) site is a product of a gene different from that coding for the enzymatic component that generates cyclic AMP.