RESUMEN
Apigenin, a dietary bioflavonoid with anticarcinogenic properties, was highly cytotoxic for HeLa cells (incubated with 0.5% FBS). This effect was accompanied with a marked increase in ERK1/2 but not MEK1/2 phosphorylation. The cytotoxic effects of apigenin were attenuated by the stimulation of these cells with 10% FBS, which provoked an increase in the phosphorylation levels of MEK1/2 and ERK1/2. The steps in the ERK1/2 pathway relevant to the cytotoxic effects of apigenin, as well as the contribution of other signaling pathways, were investigated. The activation of the pathway by transfection with the constitutively active Ras mutant (RasV12) conferred protection to serum-starved HeLa cells against apigenin, whereas the constitutively active MEK(E) mutant did not. MEK inhibitors (PD098059 or U0126) blocked ERK1/2 phosphorylation induced by apigenin and conferred partial protection against this flavonoid. The effects of apigenin did not involve p38-MAPK or JNK1/2, and were not simply due to inhibition of PI3kinase or protein kinase CK2. These data suggest that the deregulation of the ERK1/2 pathway, due to the potentiation of ERK1/2 phosphorylation without increasing MEK1/2 phosphorylation, is involved in apigenin-induced HeLa cell death.
Asunto(s)
Antineoplásicos/toxicidad , Muerte Celular/fisiología , Flavonoides/toxicidad , Sistema de Señalización de MAP Quinasas/fisiología , Quinasas de Proteína Quinasa Activadas por Mitógenos/metabolismo , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Apigenina , Proteínas Sanguíneas/deficiencia , Quinasa de la Caseína II , Muerte Celular/efectos de los fármacos , Citotoxinas/toxicidad , Inhibidores Enzimáticos/farmacología , Células HeLa , Humanos , Sistema de Señalización de MAP Quinasas/efectos de los fármacos , Proteína Quinasa 8 Activada por Mitógenos , Quinasas de Proteína Quinasa Activadas por Mitógenos/efectos de los fármacos , Quinasas de Proteína Quinasa Activadas por Mitógenos/genética , Proteínas Quinasas Activadas por Mitógenos/efectos de los fármacos , Mutación/genética , Fosfatidilinositol 3-Quinasas/efectos de los fármacos , Fosfatidilinositol 3-Quinasas/metabolismo , Fosforilación/efectos de los fármacos , Proteínas Serina-Treonina Quinasas/efectos de los fármacos , Proteínas Serina-Treonina Quinasas/metabolismo , Transfección , Regulación hacia Arriba/efectos de los fármacos , Regulación hacia Arriba/fisiología , Proteínas Quinasas p38 Activadas por Mitógenos , Proteínas ras/genética , Proteínas ras/metabolismoRESUMEN
Protein kinase CK2 and phosphorylated ERK1/2 accumulated in nucleus after serum stimulation of quiescent HepG2 cells. Nonetheless, phospho-ERK1/2 accumulated mainly in the nuclease-extracted fraction (NE) whereas the increases in nuclear CK2 (either CK2alpha or CK2beta) occurred initially in the nuclease-resistant fraction (NR). Transient decreases in CK2 were observed in cytoplasm and NE in the first 3h but thereafter they either reverted (cytoplasm) or increased above the control (NE). CK2 levels in both NE and NR were high in cells arrested at G1/S. Maximal nuclear accumulation of CK2 was blocked by cycloheximide but little affected by PD98059, SB203580 or apigenin, all of which affected nuclear phopho-ERK1/2. Thus, nuclear accumulation of CK2 during G1 phase is independent of ERK1/2 pathway. Although this process may initially relay on intracellular redistribution of the preexisting enzyme, active protein synthesis is required to attain maximal nuclear CK2 levels.