guanosine-triphosphate and Thyroid-Neoplasms

Anaplastic thyroid carcinomas are deadly tumors that are highly invasive, particularly into the bones. Although oncogenic Ras can transform thyroid cells into a severely malignant phenotype, thyroid carcinomas do not usually harbor ras gene mutations. Therefore, it is not known whether chronically active Ras contributes to thyroid carcinoma cell proliferation, although galectin-3 (Gal-3), which is strongly expressed in thyroid carcinomas but not in benign tumors or normal glands, is known to act as a K-Ras chaperone that stabilizes and drives K-Ras.GTP nanoclustering and signal robustness. Here, we examined the possibility that thyroid carcinomas expressing high levels of Gal-3 exhibit chronically active K-Ras. Using cell lines representing three types of malignant thyroid tumors--papillary, follicular, and anaplastic--we investigated the possible correlation between Gal-3 expression and active Ras content, and then examined the therapeutic potential of the Ras inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS; Salirasib) for thyroid carcinoma. Thyroid carcinoma cells strongly expressing Gal-3 showed high levels of K-Ras.GTP expression, and K-Ras.GTP transmitted strong signals to extracellular signal-regulated kinase. FTS disrupted interactions between Gal-3 and K.Ras, strongly reduced K-Ras.GTP and phospho-extracellular signal-regulated kinase expression, and enhanced the expression of the cell cycle inhibitor p21 as well as of the thyroid transcription factor 1, which is involved in thyroid cell differentiation. FTS also inhibited anaplastic thyroid carcinoma cell proliferation in vitro and tumor growth in nude mice. We conclude that wild-type K-Ras.GTP in association with Gal-3 contributes to thyroid carcinoma malignancy and that Ras inhibition might be a useful treatment strategy against these deadly tumors.

Topics: Animals; Cell Differentiation; Cell Line, Tumor; Cell Membrane; Cell Proliferation; Cyclin-Dependent Kinase Inhibitor p21; Disease Models, Animal; Down-Regulation; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Farnesol; Galectin 3; Gene Expression Regulation, Neoplastic; Guanosine Triphosphate; Humans; Mice; Nuclear Proteins; Protein Transport; Proto-Oncogene Proteins; Proto-Oncogene Proteins p21(ras); ras Proteins; Salicylates; Signal Transduction; Thyroid Neoplasms; Thyroid Nuclear Factor 1; Transcription Factors; Xenograft Model Antitumor Assays

Topics: Adenoma; Adenylyl Cyclases; Enzyme Activation; GTP-Binding Proteins; Guanosine Triphosphate; Humans; Hyperthyroidism; Mutation; Thyroid Gland; Thyroid Neoplasms

Topics: Adenylyl Cyclases; Animals; Cell Membrane; Gangliosides; Guanosine Triphosphate; Humans; Rats; Receptors, Thyrotropin; Thyroid Gland; Thyroid Neoplasms; Thyrotropin

Topics: Adenoma; Adenylyl Cyclases; Adolescent; Adult; Aged; Alprostadil; Child; Enzyme Activation; Female; Goiter, Nodular; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Humans; Male; Middle Aged; Prostaglandins E; Receptors, Cell Surface; Receptors, Thyrotropin; Sodium Fluoride; Stimulation, Chemical; Thionucleotides; Thyroid Diseases; Thyroid Neoplasms

To determine whether the beta-blocking drug propranolol had any physiologic effect on normal (n = 14) and adenomatous (n = 15) human thyroid tissues, experiments were performed to study the binding of the beta-blockers 125I-iodocyanopindolol (125I-ICYP) and 125I-iodohydroxybenzylpindolol (125I-IHYP) and the stimulation of adenyl cyclase (AC) by isoproterenol. 125I-ICYP and 125I-IHYP failed to show high-affinity binding in 27 of 29 specimens, whereas two (one normal and one adenomatous) thyroid tissues demonstrated high-affinity binding (Kd 5.5 +/- 1 X 10(-9) M) for 125I-ICYP. Thyroid-stimulating hormone (0.3 IU/ml), guanosine triphosphate (10(-4) M), and Gpp (NH)p(10(-4) M) stimulated AC in all thyroid tissues, although in two tissues (normal) Gpp (NH)p failed to cause a significant increase. Isoproterenol (10(-4) M), in contrast, had no effect on basal AC activity or on guanosine triphosphate, and Gpp (NH) p stimulated AC activity in 26 of the 29 thyroid tissues. In one of the two tissues that increased AC in response to isoproterenol, the beta-blocking drugs propranolol hydrochloride, bunitrolol hydrochloride, and tolilprolol hydrochloride decreased AC stimulation to isoproterenol at concentrations of 10(-6) M (p less than 0.05). Higher concentrations of propranolol (10(-4) - 10(-2) M) decreased AC stimulation to thyroid-stimulating hormone (p less than 0.01), not only in this responsive tissue but also in tissues that failed to demonstrate high-affinity binding for 125I-ICYP and AC stimulation to isoproterenol (p less than 0.01). Thus most normal and adenomatous human thyroid tissues lack beta-receptors and a functioning beta-receptor AC system. High concentrations of propranolol in vitro decreased AC response by thyroid-stimulating hormone, but this is probably a nonreceptor-mediated effect.

Topics: Adenoma; Adenylyl Cyclases; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Humans; In Vitro Techniques; Iodocyanopindolol; Isoproterenol; Pindolol; Propanolamines; Propranolol; Receptors, Adrenergic, beta; Thyroid Gland; Thyroid Neoplasms; Thyrotropin

The action of thyrotropin (TSH) on plasma membranes was studied to elucidate the mechanism of hormonal regulation of malignant versus normal human thyroid tissue. Thyroid plasma membranes of six specimens of papillary or follicular carcinoma and six of adenoma, as well as adjacent normal tissue obtained from these patients, were evaluated with respect to binding of 125I-labeled TSH and stimulation of adenylate cyclase. Scatchard analysis of TSH binding revealed the presence of two species of binding sites in normal thyroid of different affinities and capacities. In 11 of 12 tumors studied, the high-affinity binding site remained intact; however, the total number of low-affinity sites was markedly lower than normal tissue. Other parameters of binding were not altered in neoplastic thyroid. In each of these tissues, the hormone responsiveness and kinetics of adenylate cyclase activation were essentially identical to those observed in normal tissue, although basal activity was typically greater in the neoplasm. One carcinoma was totally deficient in both 125I-labeled TSH binding and TSH-stimulatable adenylate cyclase, although basal activity was detected. Furthermore, adenylate cyclase of this specimen was not activated by prostaglandin, in contrast to normal thyroid and other thyroid tumors. These results suggest that: (a) clinical behavior of thyroid carcinomas may not be reflected by TSH receptor-adenylate cyclase function; (b) lack of clinical response as manifest by tumor regression cannot be ascribed to the absence of functional TSH receptors or adenylate cyclase; and (c) decreased low-affinity binding present in tumors is not correlated with altered hormone responsiveness of adenylate cyclase but may reflect more general cancer-induced changes in membrane structure or composition.

Topics: Adenoma; Adenylyl Cyclases; Carcinoma; Cell Membrane; Enzyme Activation; Guanosine Triphosphate; Humans; Receptors, Cell Surface; Sodium Fluoride; Thyroid Neoplasms; Thyrotropin