RESUMEN
Choline is an essential anabolic substrate for the synthesis of phospholipids. Choline kinase phosphorylates choline to phosphocholine that serves as a precursor for the production of phosphatidylcholine, the major phospholipid constituent of membranes and substrate for the synthesis of lipid signaling molecules. Nuclear magnetic resonance (NMR)-based metabolomic studies of human tumors have identified a marked increase in the intracellular concentration of phosphocholine relative to normal tissues. We postulated that the observed intracellular pooling of phosphocholine may be required to sustain the production of the pleiotropic lipid second messenger, phosphatidic acid. Phosphatidic acid is generated from the cleavage of phosphatidylcholine by phospholipase D2 and is a key activator of the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/AKT survival signaling pathways. In this study we show that the steady-state concentration of phosphocholine is increased by the ectopic expression of oncogenic H-Ras(V12) in immortalized human bronchial epithelial cells. We then find that small interfering RNA (siRNA) silencing of choline kinase expression in transformed HeLa cells completely abrogates the high concentration of phosphocholine, which in turn decreases phosphatidylcholine, phosphatidic acid and signaling through the MAPK and PI3K/AKT pathways. This simultaneous reduction in survival signaling markedly decreases the anchorage-independent survival of HeLa cells in soft agar and in athymic mice. Last, we confirm the relative importance of phosphatidic acid for this pro-survival effect as phosphatidic acid supplementation fully restores MAPK signaling and partially rescues HeLa cells from choline kinase inhibition. Taken together, these data indicate that the pooling of phosphocholine in cancer cells may be required to provide a ready supply of phosphatidic acid necessary for the feed-forward amplification of cancer survival signaling pathways.
Asunto(s)
Colina Quinasa/metabolismo , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Proteínas Proto-Oncogénicas c-akt/metabolismo , Transducción de Señal , Animales , Western Blotting , Línea Celular Transformada , Colina Quinasa/genética , Femenino , Células HeLa , Humanos , Espectroscopía de Resonancia Magnética , Ratones , Ratones Desnudos , Neoplasias Experimentales/genética , Neoplasias Experimentales/metabolismo , Neoplasias Experimentales/patología , Ácidos Fosfatidicos/metabolismo , Fosfatidilcolinas/metabolismo , Fosforilcolina/metabolismo , Interferencia de ARN , Análisis de Supervivencia , Trasplante Heterólogo , Carga Tumoral , Proteínas ras/genética , Proteínas ras/metabolismoRESUMEN
The acid-soluble components of mouse-liver cytosol, prepared at time intervals after intragastric administration of a single carcinogenic dose of 14C-dimethylnitrosamine, were separated by column chromatography. The columns were calibrated with known in vitro metabolites of the nitrosamine, and the elution profiles were compared with those of the mouse-liver system. The results suggest that the 14C-methyl label is transferred to many of the same compounds as identified in vitro, but that numerous other labeled compounds are also present. The possible significance of these metabolites to the pathogenic processes induced by dimethylnitrosamine has yet to be determined.
