guanylyl-imidodiphosphate and Osteosarcoma

Parathyroid hormone (PTH) sensitive adenylyl cyclase activity (ACA) in SaOS-2 cells varies as a function of cell passage. In early passage (EP) cells (< 6), ACA in response to PTH and forskolin (FOR) was relatively low and equivalent, whereas in late passage (LP) cells (> 22), PTH exceeded FOR dependent ACA. Potential biochemical mechanisms for this passage dependent change in ACA were considered. In EP, prolonged exposure to pertussis toxin (PT) markedly enhanced ACA activity in response to PTH, Isoproterenol and Gpp(NH)p, whereas ACA in response to FOR was decreased. In contrast, the identical treatment of LP with PT diminished all ACA in response to PTH, Gpp(NH)p, and FOR. The dose dependent effects of PT on subsequent [(32)P]ADP-ribosylation of its substrates, GTPase activity, as well as FOR-dependent ACA, were equivalent in EP and LP. The relative amounts of G(alpha)i and G(alpha)s proteins, as determined both by Western blot, PT and cholera toxin (CT) dependent [(32)P]ADP-ribosylation, were quantitatively similar in EP and LP. Western blot levels of G(alpha)s and G(alpha)i proteins were not influenced by prior exposure to PT. Both PT and CT dependent [(32)P]ADP-ribosylation were dose-dependently decreased following exposure to PT. However, the PT-dependent decline in CT-dependent [(32)P]ADP-ribosylation occurred with enhanced sensitivity in LP. The protein synthesis inhibitor cycloheximide partially reversed the PT associated decrease in FOR dependent ACA in EP. In contrast, cycloheximide completely reversed the PT associated decrease in FOR and as well as PTH dependent ACA in LP. G(alpha)s activity, revealed by cyc(-) reconstitution, was not altered either by cell passage or exposure to PT. The results suggest that the coupling between the components of the complex may be pivotally important in the differential responsiveness of early and late passage SaOS-2 cells to PTH.

Topics: Adenylate Cyclase Toxin; Adenylyl Cyclases; Bone Neoplasms; Cell Differentiation; Cholera Toxin; Cyclic AMP; Dose-Response Relationship, Drug; Enzyme Activation; GTP Phosphohydrolases; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Humans; Osteoblasts; Osteosarcoma; Parathyroid Hormone; Pertussis Toxin; Protein Synthesis Inhibitors; Time Factors; Tumor Cells, Cultured; Virulence Factors, Bordetella

Exposure of ROS 17/2.8 cells to dexamethasone (DEX) or retinoic acid (RA) increases and decreases, respectively, adenylate cyclase activity (ACA) in response to isoproterenol, forskolin, guanylylimidodiphosphate, or NaFl. Despite dramatic changes in ACA, there were no significant changes in levels of cholera toxin- or pertussis toxin (PT)-dependent ADP-ribosylation of membranes prepared from cells after DEX or RA exposure as compared to controls. Similarly, immunochemical detection of alpha S, alpha i1-3, and alpha O, as well as Northern blot analysis of messenger RNA for each of the respective GTP binding proteins, also failed to demonstrate an influence of DEX or RA when contrasted with controls. In a novel use of the cyc- reconstitution assay, wherein the influence of inhibitory guanine nucleotide binding proteins in the extracts of control, DEX-, and RA-treated membranes is removed by a previous 24-h incubation with PT in the intact cell, we demonstrate that this PT treatment markedly enhances ACA in the cyc- reconstitution assay for all three preparations, but that the fold-increase due to PT-treatment is greatest in RA-treated cells. The greater magnitude of the effect of PT on RA-treated ROS 17/2.8 cells, in the absence of any obvious quantitative changes in the levels of the PT substrates, suggests that the effect of RA on ROS 17/2.8 cells appears to be an augmentation of the influence of inhibitory guanine nucleotide binding proteins, ultimately leading to reduced ACA.

Topics: Adenosine Diphosphate Ribose; Adenylyl Cyclases; Amino Acid Sequence; Blotting, Northern; Cell Membrane; Colforsin; Dexamethasone; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanylyl Imidodiphosphate; Isoproterenol; Molecular Sequence Data; Osteosarcoma; RNA, Messenger; Sodium Fluoride; Tretinoin; Tumor Cells, Cultured

We have used both biochemical and morphological techniques to characterize PTH receptors on the clonal osteosarcoma cell line UMR-106, a widely used model of the osteoblast phenotype. 125I-labeled rat (r) PTH-(1-34) bound to a single class of specific saturable receptors on both whole cells and membranes prepared from UMR-106 cells in a time- and temperature-dependent manner. A decrease in PTH receptor affinity seen in the presence of guanine nucleotides demonstrated that PTH receptors on the UMR-106 cells are coupled to guanyl nucleotide-binding proteins. Although PTH is a potent stimulator of adenylate cyclase in the UMR-106 cells, comparison of PTH-stimulated adenylate cyclase and PTH binding curves indicated the presence of receptors that are not linked to the adenylate cyclase system. Our studies also demonstrated that 125I-labeled rPTH-(1-34) bound to UMR-106 cells is rapidly internalized at 22 C, whereas PTH bound at 4 C remains intact and on the cell surface. Internalization of 125I-labeled rPTH-(1-34) was associated with degradation and release of the hormone at 22 C. Three morphologically distinct cell types were identified in subconfluent cultures of UMR-106 cells. Autoradiographic analysis of 125I-labeled rPTH-(1-34) binding demonstrated differential PTH receptor expression in these cell types. The most abundant PTH binding was observed over a cell type with long cytoplasmic extensions. This cell was reminiscent of the predominant PTH target cell previously identified in the rat metaphysis in vivo, suggesting that the UMR-106 cell line may represent neoplastic transformation of the PTH target cell.

Topics: Adenylyl Cyclases; Animals; Cell Membrane; Cytoplasm; Enzyme Activation; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Osteosarcoma; Parathyroid Hormone; Peptide Fragments; Rats; Receptors, Cell Surface; Receptors, Parathyroid Hormone; Teriparatide; Tumor Cells, Cultured

We have examined the mechanisms of homologous and heterologous regulation of PTH receptor binding and receptor-mediated adenylate cyclase activity in the osteosarcoma cell line UMR-106. Pretreatment with PTH resulted in a time- and dose-dependent decrease in PTH-stimulated adenylate cyclase which was maximal after 2 h and at a concentration of 10(-8) M rat (r)PTH-(1-34). PTH pretreatment over the same dose range also diminished receptor binding of 125I-labeled rPTH-(1-34); however, maximal loss of binding required 14 h and was greater than the loss of maximal adenylate cyclase activity. After 24 h pretreatment with rPTH-(1-34), cell surface receptors were decreased from 21,000 sites per cell to 2,700 sites per cell, and these down-regulated PTH receptors could not be detected in either vesicular or cytosolic subcellular fractions. Recovery from such homologous down-regulation appeared to require new receptor synthesis. Heterologous down-regulation of PTH receptors was demonstrated when UMR-106 cells were preincubated with prostaglandin E2 or (Bu)2cAMP. Heterologous desensitization was shown to be the result of a reversible modification of the PTH receptor which decreased binding affinity and decreased PTH-stimulated adenylate cyclase. Postreceptor components were also examined, and PTH but not prostaglandin E2 pretreatment was shown to decrease guanyl nucleotide binding (G) protein-mediated adenylate cyclase stimulation. This decrease in G protein function was associated with a loss of cholera toxin-catalyzed ADP ribosylation and was also detected by immunoblotting. These results indicate that PTH responses in osteoblastic cells are modulated by diverse mechanisms involving modifications both to the receptor and to postreceptor components of adenylate cyclase.

Topics: Adenosine Diphosphate Ribose; Adenylyl Cyclases; Animals; Blotting, Western; Bucladesine; Cholera Toxin; Dinoprostone; Down-Regulation; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Neoplasm Proteins; Osteoblasts; Osteosarcoma; Parathyroid Hormone; Parathyroid Hormone-Related Protein; Peptide Fragments; Proteins; Rats; Receptors, Cell Surface; Receptors, Parathyroid Hormone; Tumor Cells, Cultured

In human osteosarcoma membranes, gold(III) (Au(III)) inhibits prostaglandin E2- and isoproterenol-mediated stimulation of adenylate cyclase activity without affecting basal enzyme activity. Forskolin activation of adenylate cyclase is also blocked by Au(III) with ID50 of 1-2 microM. The inhibition by Au(III) is preserved in membranes prepared from pertussis toxin-treated cells. The inhibitory effect of Au(III) is additive to inhibition of adenylate cyclase by 2',5'-dideoxyadenosine. These data provide evidence that the action of Au(III) is at or near the catalytic moiety of the cyclase system and that Au(III) does not act via the guanine nucleotide-binding inhibitory component or the adenosine P-site inhibitory pathway.

Topics: Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Cell Line; Cell Membrane; Colforsin; Deoxyadenosines; Dideoxyadenosine; Dinoprostone; Gold; Guanylyl Imidodiphosphate; Humans; Isoproterenol; Kinetics; Osteosarcoma; Prostaglandins E

Treatment of ROS 17/2.8 cells with dexamethasone (dex) increases (-)isoproterenol (ISO)-, PTH-, cholera toxin-, guanine nucleotide-, NaF-, and forskolin-stimulated adenylate cyclase activity. Enhanced hormone stimulation was first apparent 12 h after dex addition. (-)-[3H]Dihydroalprenolol binding, displaceable by ISO, increased up to 2-fold in dex-treated cells. This effect depended on protein synthesis and closely paralleled the extent and time course of the increase in adenylate cyclase stimulation. In dex-treated cells there was also an increase in the maximum velocity of guanyl-5'-yl imidodiphosphate-stimulated adenylate cyclase, a decrease in the lag time for guanyl-5'-yl imidodiphosphate enzyme activation in the presence of ISO from 3 to 1 min, increased stimulation of adenylate cyclase by cholera toxin, and increased labeling of 47,000 and 42,000 mol wt proteins by [32P]NAD in the presence of cholera toxin. [32P]NAD ribosylation in the presence of pertussis toxin resulted in the labeling of 40,000 mol wt protein, which was also increased by 20-50% in dex-treated cells. However, pertussis toxin treatment did not augment or reduce the effect on hormone stimulation, although it increased the cAMP response to PTH and (-)ISO. These findings suggest that dex increases (-)ISO stimulation of adenylate cyclase in ROS 17/2.8 cells by jointly increasing the number of hormone receptors and the abundance of Gs, the guanine nucleotide binding regulatory protein.

Topics: Adenosine Diphosphate Ribose; Adenylyl Cyclases; Animals; Cell Line; Cholera Toxin; Cyclic AMP; Cycloheximide; Dexamethasone; Dihydroalprenolol; Enzyme Activation; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Isoproterenol; Kinetics; Molecular Weight; NAD; Osteosarcoma; Rats; Receptors, Adrenergic, beta

To study regulation of the parathyroid hormone (PTH)-responsive adenylate cyclase of osteoblast-like cells by 1,25-dihydroxyvitamin D (1,25(OH)2D), cAMP levels and adenylate cyclase activity were assayed in the hormone-responsive ROS 17/2.8 rat osteosarcoma cell line. Treatment of cells with 1,25(OH)2D3: alone markedly attenuated the cAMP response to subsequent PTH; decreased adenylate cyclase stimulated by PTH; and completely antagonized the positive regulatory effects of cell treatment with glucocorticosteroid (GC) on these responses to PTH. Sterol receptor mediation was indicated by specificity for the 1,25(OH)2D metabolite and high sensitivity (half-maximal attenuation at 7 X 10(-11) M). The effects of 1,25(OH)2D and GC were primarily on the maximal activity of adenylate cyclase and not on sensitivity to Mg2+, guanine nucleotide, or PTH. GC augmentation of ROS 17/2.8 cell cAMP accumulation was also seen with another receptor agonist (beta-adrenergic), cholera toxin or forskolin; 1,25(OH)2D antagonized all these GC effects. Opposing effects of GC and 1,25(OH)2D were seen as well on activation of the guanine nucleotide-binding regulatory protein (Ns) by guanyl-5'-yl imidodiphosphate and F- and on activation of the catalyst (C) by Mn2+. In contrast, with the activators other than PTH, cell treatment with 1,25(OH)2D in the absence of GC produced only minor attenuation of cAMP accumulation and no effect on adenylate cyclase activities. The data suggest that GC acts strongly on or near the PTH receptor-Ns complex in ROS 17/2.8 and to a lesser degree on the Ns-C interaction. Direct GC enhancement of C could not be concluded because of the influence of Ns on forskolin action and present data that Mn2+ does not uncouple Ns from C in this system. A GC effect on membrane structure or composition, as seen in other cell types, could explain these changes in adenylate cyclase function without the need to postulate multiple mechanisms. The data dissociate two 1,25(OH)2D effects, direct attenuation of activation of Ns via the PTH receptor and interference with the as yet undefined mechanism(s) of GC augmentation. These may represent dissimilar pathways of 1,25(OH)2D action on osteoblasts.

Topics: 1-Methyl-3-isobutylxanthine; Adenylyl Cyclases; Animals; Calcitriol; Cell Line; Cholera Toxin; Colforsin; Cyclic AMP; Diterpenes; Glucocorticoids; Guanylyl Imidodiphosphate; Isoproterenol; Osteoblasts; Osteosarcoma; Parathyroid Hormone; Time Factors; Triamcinolone Acetonide

Treatment of ROS 17/2.8 osteosarcoma-derived cells with dexamethasone potentiates the PTH stimulation of adenylate cyclase in these cells, yielding a detectable response to as little as 10 pM PTH. Isoproterenol stimulation was also enhanced. The dexamethasone effect is first apparent at 12 h and increases with time of treatment. The apparent EC50 for dexamethasone is 3 nM. Hydrocortisone and corticosterone act similarly to dexamethasone, but require 30-fold higher concentrations. Dexamethasone treatment produces no change in high affinity phosphodiesterase activity. Glucocorticoid-potentiating effects are much more pronounced in whole cells than in broken cells and do not influence forskolin stimulation. Particulate fractions of dexamethasone-treated cells have higher adenylate cyclase specific activity, but are stimulated by guanyl-5'-yl imidodiphosphate to the same extent as control cells. These findings suggest that the glucocorticoids potentiate hormone responsiveness through promotion of hormone receptor-adenylate cyclase coupling by a mechanism dependent on cellular integrity.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Adenylyl Cyclases; Animals; Cell Line; Colforsin; Corticosterone; Cyclic AMP; Dexamethasone; Diterpenes; Dose-Response Relationship, Drug; Guanylyl Imidodiphosphate; Hydrocortisone; Isoproterenol; Mice; Osteosarcoma; Parathyroid Hormone; Time Factors

A clonal cell line from rat osteosarcoma was found to possess parathyroid hormone and isoproterenol sensitive adenylate cyclase. This study examines the relationship between the two hormones and triphosphoguanine nucleotide with respect to enzyme activation. Concentration-dependence curves, analyzed by computer-aided curve fitting, revealed: (1) in the presence of 5 microM GTP there were two apparent affinities for parathyroid hormone (Km 9 and 89 nM) and isoproterenol (Km 72 and 340 nM; (2) and two affinities for guanosine-5' (beta, gamma-imido)triphosphate (Km 0.25 and 1.3 microM); (3) hormones and guanine nucleotides reciprocally shifted each other's concentration dependence curve to the high affinity sites; (4) parathyroid hormone and isoproterenol interacting with high affinity sites competed for the same adenylate cyclase; (5) parathyroid hormone and isoproterenol, acting on low affinity sites had additive effects and also stimulated adenylate cyclase in the absence of added guanine nucleotides. The findings are consistent with (i) competition of parathyroid hormone and isoproterenol for the activation of the high (hormone) affinity complex containing: receptors, nucleotide subunit, triphosphoguanine nucleotide, catalytic unit (ii) the apparent presence of receptor-nucleotide sub-unit GDP-catalytic unit complexes with low hormone affinity which are stimulated by parathyroid hormone and isoproterenol separately.

Topics: Adenylyl Cyclases; Animals; Binding Sites; Binding, Competitive; Cattle; Cell Line; Dose-Response Relationship, Drug; Guanylyl Imidodiphosphate; Isoproterenol; Osteosarcoma; Parathyroid Hormone; Rats; Receptors, Adrenergic, beta

1. Mg2+ concentration dependence of adenylate cyclase activity, in a rat osteosarcoma cell line (ROS 2/3), exhibits two apparent affinities with Km values of approx. 2 mM and 10 mM. 2. Only one Mg2+ affinity with a Km value of around 1 mM was apparent at saturating concentrations of: (i) guanosine-5'-(beta, gamma-imido)triphosphate; (ii) parathyroid hormone and GTP; and (iii) (-)-isoproterenol and GTP. 3. Conversely, at saturating concentrations of Mg2+ (40 mM) only high hormone concentrations, acting on low affinity sites, stimulated adenylate cyclase. 4. At saturating concentrations of guanosine-5'-(beta, gamma-imido)triphosphate, hormone stimulation decreased with increasing Mg2+ concentrations and none was seen at 40 mM Mg2+. The findings suggest that hormone stimulation of adenylate cyclase is associated with Mg2+ activation of a 'high hormone affinity' responsive state dependent on triphosphoguanine nucleotide. The hormone effect on Mg2+ affinity fully accounts for hormone stimulation of adenylate cyclase at physiologically relevant concentrations.

Topics: Adenylyl Cyclases; Animals; Cattle; Cell Line; Dose-Response Relationship, Drug; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Isoproterenol; Kinetics; Magnesium; Osteosarcoma; Parathyroid Hormone; Rats

The effects of Mg(2+) and Ca(2+) on bone and osteosarcoma adenylate cyclase were investigated. The concentrations of the cations and other ionic species in the assay mixture were calculated by solving the simultaneous equations describing the relevant ionic interactions (multiple equilibria). We re-examined the effects of HATP(3-) and ATP(4-) on enzyme activity and found that (i) the concentration of the minor ATP species is less than 1% of that of MgATP(2-), and their ratio to MgATP(2-) is constant if Mg(2+) and H(+) concentrations are unchanged; (ii) Mg(2+) addition decreased the ratio of the minor species to MgATP(2-) and increased the enzyme activity, but no meaningful kinetic model could attribute this effect of HATP(3-) or ATP(4-). On the other hand, kinetic analysis of Mg(2+) effects showed: (i) stimulation via two metal sites, separate from the catalytic (MgATP(2-)) site, with apparent K(m) values of approximately 1 and 8mm; (ii) that the low affinity increased towards the higher one when the enzyme activity rose as a result of increased substrate or guanine nucleotide concentrations, this effect being less pronounced in tumour; (iii) conversely, that two apparent affinities for MgATP(2-) merged into one at high Mg(2+) concentration; (iv) kinetically, that this relationship is of the mixed con-competitive type, which is consistent with a role for Mg(2+) as a requisite activator, and binding occurring in non-ordered sequence. Analysis of the Ca(2+) effects showed: (i) competition with Mg(2+) at the metal site (K(i) 20mum for bone and 40mum for tumour); (ii) that relative to the substrate the inhibition was uncompetitive, i.e. velocity decreased and affinity increased proportionally, which is consistent with Ca(2+) binding after substrate binding. These findings support the existence of interacting enzyme complexes, losing co-operativity at increased enzyme activity. They also indicate a potential physiological role for Ca(2+) in enzyme regulation and point to quantitative differences between bone and tumour with regard to these properties.

Topics: Adenosine Triphosphate; Adenylyl Cyclases; Animals; Bone and Bones; Calcium; Cell Membrane; Egtazic Acid; Guanylyl Imidodiphosphate; In Vitro Techniques; Kinetics; Magnesium; Osteosarcoma; Rats; Sarcoma, Experimental

The purpose of this study was to compare the adenylate cyclase of a tumour (rat osteosarcoma) growing in vivo with that of fast-growing embryonic bone. In the tumour the enzyme activity per total protein or DNA (under the same assay conditions) was 6--10-fold lower than in embryonic bone. To characterize this difference, we examined the kinetic properties of the enzyme in partially purified plasma membranes from the two tissues. A purification procedure based on differential centrifugation and discontinuous-sucrose-gradient centrifugation yielded a 10-fold increase in the specific activities of adenylate cyclase and 5'-nucleotidase in bone. The same procedure yielded an enriched membrane preparation from the tumour, but, relative to 5'-nucleotidase, a loss of 30% in adenylate cyclase occurred, which could not be recovered from another fraction. Kinetic analysis revealed that the lower adenylate cyclase activity in the tumour was due to a decrease in Vmax.. There was no significant difference in Ks (approx. 0.15 mM), and in the Km for GTP and p[NH]ppG. There were marked differences, however, in the extent of stimulation by p[NH]ppG, GTP and hormone, which was greater in tumour, and in the K1 for adenosine inhibition, which was 140 microM in bone and 500 microM in tumour. Under maximum stimulatory conditions, the enzyme activity in the tumour approached that in bone. The kinetic differences between bone and tumour enzyme were decreased by detergent solubilization, suggesting that the membrane environment plays a role in the generation of the observed differences.

Topics: Adenylyl Cyclases; Animals; Bone and Bones; Cell Membrane; Guanosine Triphosphate; Guanylyl Imidodiphosphate; In Vitro Techniques; Kinetics; Osteosarcoma; Parathyroid Hormone; Rats; Sarcoma, Experimental; Stimulation, Chemical; Subcellular Fractions

Adenylate cyclase activity in particulate fractions from a transplantable rat osteogenic sarcoma was stimulated in a dose-dependent manner by prostaglandins E1 and E2 (PGE1 and PGE2) and parathyroid hormone (PTH). Prostaglandin F2alpha was active at a high concentration (3 x 10(-4) mol/l). Pretreatment of membranes with collagenase plus hyaluronidase reduced the magnitude of the PTH effect but did not affect the size of the PGE1 effect. Guanosine 5'-triphosphate and its synthetic analogue 5'-guanylylimidodiphosphate (Gpp(NH)p) activated adenylate cyclase in particulate preparations from the osteogenic sarcoma. The latter agent produced much larger effects, although the concentrations required for half-maximal enzyme activation were the same for both agonists (approximately 2 x 10(-6) mol/l). The effects of PTH and Gpp(NH)p were supra-additive at some concentrations of hormone. The effects of PGE1 and Gpp(NH)p were supra-additive at all hormone concentrations tested. Pre-incubation of membrane particles for 6 min with PTH produced an enzyme activation which was not reversed by dilution through washing; pre-incubation with PGE1 did not produce this effect. The response of membrane adenylate cyclase to Gpp(NH)p (10(-4) mol/l) was 75% greater in preparations pre-incubated with PTH than in membranes pre-incubated in buffer alone or in buffer containing PGE1. The basal rate of cyclic AMP production in the adenylate cyclase assay system decreased over a 35 min incubation period. This decrease was prevented by addition of PTH or PGE1. Addition of NaF or Gpp(NH)p produced a steady increase in the rate of production of cyclic AMP with time. Membrane preparations did not reduce the biological activity of PTH and did not degrade 125I-labelled PTH. The results demonstrate that the PTH- and PGE-responsive adenylate cyclases of the osteogenic sarcoma have distinctly different properties and that particulate preparations of the tumour do not metabolize PTH.

Topics: Adenylyl Cyclases; Animals; Cell Membrane; Dose-Response Relationship, Drug; Guanosine Triphosphate; Guanylyl Imidodiphosphate; In Vitro Techniques; Osteosarcoma; Parathyroid Hormone; Prostaglandins E; Prostaglandins F; Rats; Sarcoma, Experimental

Topics: Adenylyl Cyclases; Animals; Cell Membrane; Cytosol; Egtazic Acid; Enzyme Activation; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Molecular Weight; Neoplasm Proteins; Neoplasms, Experimental; Osteosarcoma; Rats