RESUMEN
Transformation of thyroid cells with either K-ras or H-ras viral oncogenes produces cell types with different phenotype and different response to the inhibition of the prenylation pathway by 3-hydroxy-3-methylglutaryl-CoA reductase or farnesyltransferase inhibitors. These inhibitors induce apoptosis in K-ras-transformed FRTL-5 cells (FRTL-5-K-Ras) whereas cell cycle arrest is induced in H-ras-transformed FRTL-5 (FRTL-5-H-Ras). In FRTL-5-K-Ras cells, the product of K-ras gene is implicated in the scavenging of reactive oxygen species (ROS) through the activation of extracellular-signal-regulated kinase (ERK)1/2 kinases. We observed that lovastatin blocked ras activation through inhibition of farnesylation and induced apoptosis, increasing ROS levels through inhibition of ERK1/2 signaling and Mn-SOD expression. Lovastatin-induced apoptosis was due to intracellular ROS increase since both, the antioxidant compound pyrrolidinedithiocarbamate or the SOD-mimetic compound, antagonized apoptosis. Moreover, both p38 mitogen-activated protein kinase and nuclear factor kappaB pathways, activated as a consequence of high ROS levels, are involved in the apoptotic effect, indicating that cell death induced by lovastatin was dependent on oxidative stress. Lovastatin antitumor efficacy in K-ras-dependent thyroid tumors was further confirmed in vivo, proposing a new therapeutic strategy for those tumor diseases that are sustained by an inappropriate K-ras expression.
Asunto(s)
Antineoplásicos/farmacología , Lovastatina/farmacología , Glándula Tiroides/citología , Glándula Tiroides/efectos de los fármacos , Animales , Antineoplásicos/metabolismo , Apoptosis , Ciclo Celular/efectos de los fármacos , Línea Celular , Transformación Celular Neoplásica , Femenino , Genes ras , Lovastatina/metabolismo , Masculino , Ratones , Ratones Desnudos , Prenilación , Ratas , Especies Reactivas de Oxígeno/metabolismo , Transducción de Señal/efectos de los fármacos , Glándula Tiroides/metabolismoRESUMEN
The aim of this study was to evaluate in vivo the antiproliferative effect of an inhibitor of isoprenoids metabolism, lovastatin, in an experimental model of propylthiouracil-induced goiter. In thyroid cells, thyrotropin (TSH)-induced proliferation requires active isoprenoid synthesis, and the HMG-CoA reductase inhibitors have antiproliferative effects in vitro. Propylthiouracil treatment (PTU) of rats led to thyroid hypertrophy and hyperplasia by TSH-induced activation of the mitogen-activated protein kinase (MAPK) pathway. Immunohistochemistry showed an increased number of proliferating cell nuclear antigen (PCNA)-positive cells in the thyroid gland of PTU-treated rats. Moreover, the phosphorylation of ERK1 and ERK2 was increased in the extract from goiter tissue as compared with the thyroid tissue of untreated rats. To determine whether the inhibition of selected pro-survival pathways (i.e., p21ras-MAPK) was sufficient to affect goitrogenesis, thyroids from 12 PTU-treated rats were injected in vivo with an adenovirus transducing a dominant-negative ras gene (Rad-L61.S186) and another set of 12 rats were injected with a pharmacological inhibitor of MAPK (PD98059). Both Rad-L61.S186 and PD98059 were able to inhibit the PTU-induced goiter. It is interesting to note that lovastatin, when administered in drinking water, significantly prevented the thyroid gland enlargement. Therefore, lovastatin-treated thyroid glands were significantly smaller than those treated with PTU alone. In addition, the lovastatin-treated glands also showed a decreased expression of phosphorylated ERK1/2 and a number of PCNA-positive cells. Our data suggest that lovastatin is an efficient inhibitor of goitrogenesis and provide a rationale for innovative therapeutic strategies employing statins in the treatment of nodular goiter in humans.
Asunto(s)
Bocio/prevención & control , Inhibidores de Hidroximetilglutaril-CoA Reductasas/farmacología , Lovastatina/farmacología , Sistema de Señalización de MAP Quinasas/efectos de los fármacos , Glándula Tiroides/efectos de los fármacos , Proteínas ras/metabolismo , Animales , Modelos Animales de Enfermedad , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Flavonoides/farmacología , Técnicas de Transferencia de Gen , Bocio/inducido químicamente , Bocio/metabolismo , Bocio/patología , Inhibidores de Hidroximetilglutaril-CoA Reductasas/uso terapéutico , Hiperplasia , Hipertrofia , Lovastatina/uso terapéutico , Masculino , Fosforilación , Antígeno Nuclear de Célula en Proliferación/análisis , Propiltiouracilo , Inhibidores de Proteínas Quinasas/farmacología , Prenilación de Proteína/efectos de los fármacos , Ratas , Ratas Wistar , Terpenos/metabolismo , Glándula Tiroides/metabolismo , Glándula Tiroides/patología , Tirotropina/sangre , Proteínas ras/genéticaRESUMEN
The physiological effects of a variety of N6-substituted adenine and adenosine derivatives called cytokinins have been documented in plants, but information on their occurrence and function in other biological system is limited. Here we investigated the anti-proliferative effect of N6-isopentenyladenosine (i6A), an adenosine and isoprenoid derivative, in a thyroid cell system, FRTL-5 wild-type, and K-ras transformed KiMol cells. Addition of i6A to FRTL-5 cells caused a dose-dependent arrest of the G0-G1 cell phase transition associated with a reduction of cells in the S phase that was much more evident in KiMol cells. I6A arrested tumor cell proliferation by inhibiting farnesyl diphosphate synthase (FPPS) and protein prenylation. Indeed the addition of farnesol reversed these effects and i6A affected protein prenylation, in particular lamin B processing. I6A effect was not mediated by the adenosine receptor but was due to a direct modulation of FPPS enzyme activity as a result of its uptake inside the cells. I6A inhibited FPPS activity more efficaciously in KiMol cells than in normal FRTL-5. Moreover, the i6A anti-proliferative effect was evaluated in vivo in a nude mouse xenograft model, where KiMol cells were implanted subcutaneously. Mice treated with i6A showed a drastic reduction in tumor volume. Our findings indicate that this isoprenoid end product might be used for antineoplastic therapy, an application emulating that of the lovastatin and/or farnesyl-transferase inhibitors