β-Adrenergic Receptors in Pediatric Tumors: Uncoupled β₁-Adrenergic Receptor in Ewing's Sarcoma

β-Adrenergic receptors were demonstrated in membrane preparations from 6 human Ewing's sarcomas and compared to thCJse from 46 other pediatric cancers with the use of the β-adrenergic antagonist (-)-[₃H]dihydroalprenolol [(-)-[₃H]DHA]. In contrast to the high numbers of receptor sites found in Ewing's sarcomas (55-640 fmol mg-' protein; dissociation constant K_d, 1–2 nM), other childhood cancers (neuroblastoma, rhabdomyosarcoma, brain tumors, lymphoma, osteosarcoma, hepatoblastoma, yolk sac, and Wilms' tumor) contained in general fewer β-adrenergic receptor sites. Characteristics of (-)-[₃H]DHA binding were therefore more fully characterized in the Ewing's tumors. Competition of (-)-[₃H]DHA binding by classical catecholamine agonists, as well as by subtype selective agents metoprolol and zinterol, demonstrated the presence of a homogeneous population of β,-adrenergic sites in several Ewing's tumors. Adenylate cyclase activity in all Ewing's sarcomas was enhanced by GTP and NaF. However, in spite of high numbers of β-adrenergic receptors, (-)-isoproterenol was not very effective in the activation of adenylate cyclase activity in several of the Ewing's tumors tested. Neither guanyl-5'-yl-imidophosphate nor GTP altered agonist potency for the receptor site in these catecholamine-insensitive tumors. Hill coefficients obtained from competition experiments with (-)isoproterenol (in the presence or absence of guanine nucleotide) were approximately 1.0. These uncoupled receptors were resistant to Nethylmaleimide denaturation and were densensitized only 50% during culture in the presence of (-)-isoproterenol. Thus Ewing's sarcomas are relatively rich in β-adrenergic sites, and several tumors appear to have a coupling lesion involving guanine nucleotide-dependent regulatory protein interaction with β-adrenergic receptors and adenylate cyclase, similar in phenotype to that described in the (unc) variant of S49 mouse lymphoma.