Expression of genes for metabolism of cyclic adenosine 3':5' monophosphate in somatic cells. β Adrenergic and PGE₁ receptors in parental and hybrid cells

Using the ligands [¹²⁵I]iodohydroxybenzylpindolol and [³H]prostaglandin E₁ ([³H]PGE₁), we have studied the relationship of receptors for β adrenergic agents and for PGE₁ to adenylate cyclase in membranes of parental, hybrid, and variant mammalian cell lines. Fusion of parental clones responsive to β adrenergic agonists (β⁺) with unresponsive clones (β^-) produced hybrid clones with a greatly diminished β adrenergic response: β⁺ x β^- → β^-. Binding studies with [¹²⁵I] iodohydroxybenzylpindolol showed a decreased concentration of β receptors in six such hybrid clones. Thus, paucity of β adrenergic receptors is probably a sufficient, albeit not necessarily complete, explanation for the decreased β adrenergic responsiveness of the hybrid clones. When a clone with β receptor but without apparent adenylate cyclase activity (HC 1) was hybridized with a β^- clone that has adenylate cyclase (B82), a responsive hybrid clone was obtained. In nine cell hybrids produced by the fusion of clones responsive (PGE₁⁺) and unresponsive (PGE₁^-) to PGE₁, high affinity binding sites for [³H]PGE₁ were expressed in the same manner as was PGE₁ sensitive adenylate cyclase: PGE₁⁺ x PGE₁ → PGE₁⁺. The chemical specificities and affinities of the parental receptors and responsive adenylate cylcases were faithfully reproduced in the hybrid clones. Activation by PGE₁ was proportional to the occupation of the high affinity receptors. In a wild type lymphoma clone (24.3.2), the concentration dependencies for binding of [³H]PGE₁ and for activation of adenylate cyclase by PGE₁ were identical. In a variant lymphoma clone (94.15.1) lacking adenylate cyclase activity, no high affinity receptors for PGE₁ were detected, whereas β adrenergic receptors have been demonstrated in this variant clone (Insel, P.A., Maguire, M.E., Gilman, A.G., Coffino, P., Bourne, H., and Melmon, K. (1976) Mol. Pharmacol. 12, 1062-1069). Hybrid cells formed by the fusion of 94.15.1 with cell line RAG (PGE₁^-) responded to PGE₁. Clone 94.15.1 may have receptors for PGE₁ of reduced affinity or in low concentration. Alternatively, RAG and 94.15.1 may have complementary genetic defects such that the RAG x 94.15.1 hybrid cells express a hormonally responsive receptor adenylate cyclase system.