beta-Adrenergic receptors in pediatric tumors: uncoupled beta 1-adrenergic receptor in Ewing's sarcoma.
beta-Adrenergic receptors were demonstrated in membrane preparations from 6 human Ewing's sarcomas and compared to those from 46 other pediatric cancers with the use of the beta-adrenergic antagonist (-)-(3H)dihydroalprenolol [(-)[3H]DHA]. In contrast to the high numbers of receptor sites found in Ewing's sarcomas (55-640 fmol x mg-1 protein; dissociation constant Kd, 1-2 nM), other childhood cancers (neuroblastoma, rhabdomyosarcoma, brain tumors, lymphoma, osteosarcoma, hepatoblastoma, yolk sac, and Wilms' tumor) contained in general fewer beta-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 beta 1-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 beta-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 the competition experiments with (-)-isoproterenol (in the presence or absence of guanine nucleotide) were approximately 1. 0. These uncoupled receptors were resistant to N-ethylmaleimide denaturation and were densensitized only 50% during culture in the presence of (-)-isoproterenol. Thus Ewing's sarcomas are relatively rich in beta-adrenergic sites, and several tumors appear to have a coupling lesion involving guanine nucleotide-dependent regulatory protein interaction with beta-adrenergic receptors and adenylate cyclase, similar in phenotype to that described in the (unc) variant of S49 mouse lymphoma.[1]References
- beta-Adrenergic receptors in pediatric tumors: uncoupled beta 1-adrenergic receptor in Ewing's sarcoma. Whitsett, J.A., Burdsall, J., Workman, L., Hollinger, B., Neely, J. J. Natl. Cancer Inst. (1983) [Pubmed]
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