8-bromocyclic-gmp and Melanoma

Cyclic nucleotide phosphodiesterases (PDEs) regulate the intracellular concentrations and effects of adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP). The role of PDEs in malignant tumor cells is still uncertain. The role of PDEs, especially PDE2, in human malignant melanoma PMP cell line was examined in this study. In PMP cells, 8-bromo-cAMP, a cAMP analog, inhibited cell growth and invasion. However, 8-bromo-cGMP, a cGMP analog, had little or no effect. PDE2 and PDE4, but not PDE3, were expressed in PMP cells. Growth and invasion of PMP cells were inhibited by erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), a specific PDE2 inhibitor, but not by rolipram, a specific PDE4 inhibitor. Moreover, cell growth and invasion were inhibited by transfection of small interfering RNAs (siRNAs) specific for PDE2A and a catalytically-dead mutant of PDE2A. After treating cells with EHNA or rolipram, intracellular cAMP concentrations were increased. Growth and invasion were stimulated by PKA14-22, a PKA inhibitor, and inhibited by N(6)-benzoyl-c AMP, a PKA specific cAMP analog, whereas 8-(4-chlorophenylthio)-2'-O-methyl-cAMP, an Epac specific cAMP analog, did not. Invasion, but not growth, was stimulated by A-kinase anchor protein (AKAP) St-Ht31 inhibitory peptide. Based on these results, PDE2 appears to play an important role in growth and invasion of the human malignant melanoma PMP cell line. Selectively suppressing PDE2 might possibly inhibit growth and invasion of other malignant tumor cell lines.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Adenine; Cell Line, Tumor; Cell Movement; Cell Proliferation; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 2; Humans; Melanoma; RNA Interference; RNA, Small Interfering; Rolipram

Adhesion of circulating tumor cells to microvascular endothelium plays an important role in tumor metastasis to distant organs. The purpose of this study was to determine whether nitric oxide (NO) would attenuate tumor cell adhesion (TCA) to naive or lipopolysaccharide (LPS)-treated postcapillary venules. A melanoma cell line, RPMI 1846, was shown to be much more adhesive to postcapillary venules isolated from rat mesentery than to corresponding precapillary arterioles. Although venules exposed to LPS for 4 h demonstrated an increased adhesivity for the melanoma cells, TCA to LPS-treated arterioles was not altered. Isolated venules exposed to DETA/NO (1 mM), an NO donor, for 30 min prior to tumor cell perfusion prevented the increment in adhesion induced by LPS and attenuated TCA to naive postcapillary venules. While L-arginine (100 microM), an NO precursor, failed to decrease TCA to naive postcapillary venules, this treatment abolished LPS-stimulated TCA to postcapillary venules. The effect of L-arginine was reversed by administration of N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM), an NO synthase (NOS) inhibitor. These observations indicate that both exogenous and endogenous NO modulate TCA to postcapillary venules. To assess the role of NO-induced activation of cGMP in the reduction in TCA produced by DETA/NO, two additional series of experiments were conducted. In the first series, LY-83583 (10 microM), a guanylyl cyclase inhibitor, was shown to completely reverse the effect of DETA/NO on TCA to both naive and LPS-activated postcapillary venules. On the other hand, administration of 8-bromoguanosine 3',5'-cyclic monophosphate (8-B-cGMP) (1 mM), a cell permeant cGMP analog, mimicked the effect of DETA/NO and reduced TCA to LPS-stimulated postcapillary venules. These data suggest that (a) tumor cells are more likely to adhere to postcapillary venules than to corresponding precapillary arterioles, (b) LPS enhances TCA to postcapillary venules, (c) both exogenously applied (DETA/NO) and endogenously generated (L-arginine) NO attenuate the enhanced adhesion induced by LPS, but only DETA/NO reduced TCA to naive postcapillary venules, and (d) the NO-induced reduction in TCA to LPS-activated postcapillary venules occurs by a cGMP-dependent mechanism.

Topics: Aminoquinolines; Animals; Arterioles; Cell Adhesion; Cell Adhesion Molecules; Cricetinae; Cyclic AMP; Cyclic GMP; DEET; Endothelium, Vascular; Enzyme Inhibitors; Guanylate Cyclase; Lipopolysaccharides; Male; Melanoma; Nitric Oxide; Nitric Oxide Synthase; Rats; Rats, Sprague-Dawley; Tumor Cells, Cultured; Venules

The effect of congeners of nitrogen monoxide (NO) on iron (Fe) uptake from 59Fe-125I-transferrin (Tf) and release of 59Fe from prelabelled cells have been investigated in SK-MEL-28 human melanoma cells, human K562 cells and mouse MDW-4 cells. These studies have been initiated as it has been suggested that the tumoricidal effects of NO may be mediated by its acting to release Fe from cells (Hibbs et al., 1984 Biochem. Biophys. Res. Commun. 123, 716-723; Hibbs et al., 1988 Biochem. Biophys. Res. Commun. 157, 87-94). The nitrosonium ion (NO+) generator, sodium nitroprusside (SNP), decreased 59Fe uptake by melanoma cells to 57% of the control without decreasing 125I-Tf uptake after a 4-h incubation with 59Fe-125-Tf (1.25 microM). Longer incubations up to 24 h decreased 59Fe uptake and also 125I-Tf uptake. Two breakdown products of SNP, ferricyanide and cyanide, had no effect on 59Fe uptake. In addition, photolysis of the SNP solution prevented the inhibition of 59Fe uptake, suggesting that NO was the active agent. Two nitric oxide (NO.) producing agents, 3-morpholinosydnonimine (SIN), and S-nitroso-N-acetylpenicillamine (SNAP), also decreased 59Fe uptake from 59Fe-125I-Tf. Superoxide dismutase increased the efficacy of SIN, and the NO-scavenger, oxyhaemoglobin, prevented the inhibition of 59Fe uptake mediated by SNAP, again suggesting that NO was the active agent. Furthermore, dialysis studies demonstrated that none of the NO-generating agents could remove 59Fe from 59Fe-125I-Tf, suggesting that the decrease in cellular Fe uptake observed was not due to NO releasing Fe from the Fe-binding sites of Tf. Despite the ability of NO-producing agents at inhibiting 59Fe uptake by cells, they could not remove significant amounts of 59Fe from melanoma cells prelabelled with either 59Fe-citrate or 59Fe-125I-Tf. Similar data were obtained using K562 and MDW-4 cells. Interestingly, the NO+ generating agent, SNP, had no effect on [3H]thymidine uptake. However, when SNP was converted to an NO. generator by the addition of 1 mM ascorbate, its effect was similar to the NO. generator, SNAP, markedly reducing [3H]thymidine incorporation to 33% of the control value. The addition of unlabelled diferric Tf (0.625 microM) to SNAP ameliorated its inhibitory effect on cellular [3H]thymidine uptake, suggesting that the interaction of NO. with Fe was of importance in the inhibition observed. The results are discussed in the context of the cytostatic potential of NO via its binding to F

Topics: Animals; Cell Line; Cyclic GMP; Humans; Iodine Radioisotopes; Iron; Iron Radioisotopes; Melanoma; Mice; Molsidomine; Nitric Oxide; Nitrites; Nitroprusside; Thymidine; Transferrin

Nitric oxide (NO) and the NO generating agent nitroprusside (SNP), inhibit the binding of [125I] vasoactive intestinal peptide (VIP) to its receptor at the surface of IGR39 human melanoma cells. Cysteine (10 mM) increases the sensitivity of the system to SNP while N-acetylcysteine (10 mM) decreases it. The NO gas as well as SNP inhibits the [125I]VIP binding capacity. These observations sustain an effect of SNP-generated NO rather than an effect of the SNP molecule per se or the cyanoferrate portion of the molecule. The inhibitory effect of NO is time and concentration dependent and is fully reversible. Affinity constants of high and low affinity VIP receptors of SNP-treated IGR39 cells are not modified while maximal binding capacity (Bmax) of both receptor types are decreased to the same extent. Production of cGMP by SNP-treated cells is time and concentration dependent and the maximum amount of cGMP obtained reaches 13 times the basal level. The cAMP production is not affected by SNP. However, the SNP effects on the [125I]VIP binding are not mimicked by the membrane permeant cGMP analogs dibutyryl cGMP and 8-bromo cGMP even at concentrations as high as 0.5 mM. Taken altogether, these data demonstrate a regulatory action of NO on VIP binding capacity of IGR39 melanoma cells which is not cGMP mediated. They also evidence a new step which could be involved in the NO-VIP interaction.

Topics: Cyclic AMP; Cyclic GMP; Dibutyryl Cyclic GMP; Humans; Melanoma; Neoplasm Proteins; Nitric Oxide; Nitroprusside; Protein Binding; Receptors, Vasoactive Intestinal Peptide; Skin Neoplasms; Tumor Cells, Cultured; Vasoactive Intestinal Peptide