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.