guanylyl-imidodiphosphate and Lung-Neoplasms

Tumorigenic mouse lung-derived type 2 cell lines have large reductions in both beta-adrenergic-stimulated cAMP production and ligand binding to beta-adrenergic receptors. These tumorigenic cells are also relatively insensitive to glucocorticoids. Because glucocorticoids regulate both beta-adrenergic receptor expression and receptor coupling to the stimulatory guanine nucleotide binding protein Gs interactions between the glucocorticoid and beta-adrenergic signalling systems were examined. This study demonstrates that beta-adrenergic ligand binding and agonist sensitivity are increased in a tumorigenic cell line stably expressing a normal glucocorticoid receptor transgene. However, although the transfected tumour cells and non-tumorigenic cells have similar amounts and affinities of beta-adrenergic agonist and antagonist binding, similar amounts of Gs subunits and similar forskolin-stimulated adenylyl cyclase activities, the former remain much less isoproterenol responsive. Competition binding studies demonstrate that tumour cell beta-adrenergic receptors have both high- and low-affinity agonist binding but are functionally uncoupled from Gs. This uncoupling may involve an alteration in Gs, as guanine nucleotides exhibit a reduced ability to stimulate adenylyl cyclase. Thus, some aspects of tumorigenic cell dysfunction in beta-adrenergic signalling can be ameliorated by interactions with the glucocorticoid pathway, but additional defects are also involved.

Topics: Adenylyl Cyclases; Animals; Cell Line; Colforsin; Dexamethasone; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Humans; Iodocyanopindolol; Isoproterenol; Lung Neoplasms; Mice; Pindolol; Receptors, Adrenergic, beta

The regulation of adenylate cyclase in murine melanoma tumor cell clones with different metastatic capacities has been studied in intact cells and isolated membrane preparations. Analysis of the responses of intact cells from a number of B16 melanoma clones revealed that treatment with melanocyte-stimulating hormone (MSH) or the diterpene, forskolin, produced significantly greater accumulation of intracellular cyclic adenosine 3',5' monophosphate (cAMP) in strongly metastatic clones than in weakly metastatic tumor cell clones. In contrast, in isolated membranes from the same panel of clones, the extent of activation by forskolin but not by MSH correlated with metastatic capacity. Sodium fluoride and 5'-guanyl-beta-gamma-imidodiphosphate [Gpp(NH)p] also stimulated adenylate cyclase in isolated membranes but the extent of activation did not correlate with the metastatic behavior of the donor cells. A combination of forskolin and Gpp(NH)p proved to be a sensitive prospective indicator for identifying differences in the metastatic capabilities of individual B16 melanoma clones. Adenylate cyclase in membrane preparations from strongly metastatic B16 clones displayed synergistic activation but stimulation of the enzyme from weakly metastatic clones was less than additive. To test the generality of these findings, similar investigations were performed on B16-BL6 melanoma cells, a highly invasive subline of the B16 melanoma, and the K1735, an ultraviolet-light-induced murine melanoma arising in a different mouse strain (C3H). Consistent with their high metastatic potential, clones derived from the B16-BL6 melanoma displayed elevated levels of hormonally-stimulated adenylate cyclase, thereby confirming, for this tumor system, a close association between hormonal responsiveness and metastatic capacity. In contrast, K1735 melanoma cell clones exhibited significant interclonal variation in adenylate cyclase activity and metastatic performance, but no consistent relationship between the two traits was detected. Differences in the regulation and/or the intrinsic catalytic capacity of adenylate cyclase may account, at least in part, for the variation in hormonal responsiveness observed among B16 clones with distinct metastatic properties and suggest that cAMP-dependent molecular processes may be required for the expression of B16 melanoma experimental metastatic potential.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Adenylyl Cyclases; Animals; Cell Membrane; Clone Cells; Colforsin; Cyclic AMP; Fluorides; Guanylyl Imidodiphosphate; Kinetics; Lung Neoplasms; Melanocyte-Stimulating Hormones; Melanoma; Mice; Neoplasm Metastasis

The presence of muscarinic and nicotinic acetylcholine receptors (m- and nAChR, respectively) in small cell carcinomas (SCC) of the lung was assessed by measurement of specific binding of (-)[3H]quinuclidinyl benzilate ([3H]QNB) and 125I-alpha-bungarotoxin, respectively. Of five SCC studied, four were originally derived from patients with the Lambert-Eaton myasthenic syndrome, an autoimmune disease of neuromuscular transmission, and one was from a patient without evidence of neurological disease. There was no evidence of nAChR, but all tumors bound (-)[3H]QNB in a saturable and specific manner. Dissociation constants derived from saturation isotherms ranged between 35.4 and 181.7 fmol/mg protein (mean values for the five SCC). Competition studies revealed a pharmacological profile consistent with previous descriptions of mAChR. Competition by pirenzepine revealed only one class of binding sites, that with a relatively low affinity for pirenzepine. In the presence of the guanine nucleotide analogue 5'-guanylyl imidodiphosphate, a decrease in affinity of the mAChR of SCC for oxotremorine was observed, with an increase in the pseudo-Hill coefficient, but there was no change in the binding of atropine. The expression on SCC of mAChR, apparently of the M2 subclass, represents yet another neural differentiation marker of SCC. It is noteworthy that the expression of this marker is not restricted to patients with an autoimmune paraneoplastic syndrome involving cholinergic neurons.

Topics: Animals; Autoimmune Diseases; Binding, Competitive; Bungarotoxins; Carcinoma, Small Cell; Cell Line; Guanylyl Imidodiphosphate; Humans; Kinetics; Lung Neoplasms; Mice; Mice, Nude; Neuromuscular Diseases; Quinuclidinyl Benzilate; Receptors, Muscarinic; Receptors, Nicotinic; Syndrome