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.
|Original language||English (US)|
|Number of pages||10|
|Journal||Journal of Biological Chemistry|
|State||Published - Jan 1 1977|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology