RESUMEN
A majority of breast cancer cases are positive for the estrogen receptor (ER), which means that they can respond to the estrogen hormone to achieve growth. Hence, the ER signaling pathway has been extensively targeted in pharmaceutical research and development in order to suppress tumor growth. However, prevalent hormone therapy and targeted therapy often become ineffective as cancer cells ultimately develop resistance, suggesting that there could be unidentified signaling molecules and events that regulate breast cancer growth. Notably, recent studies have uncovered that Piwilike (Piwil) proteins, which were initially found in germline cells, are expressed in a wide spectrum of human cancers, including breast cancers. Although Piwil proteins have been well established to silence retrotransposons and to promote heterochromatin formation in germline cells, their somatic functions in cancer cells remain largely unknown. In the present study, we profiled the expression of four Piwi homologs in an ERpositive breast cancer cell line, MCF7, and found that only Piwil4 was upregulated by 17ßestradiol treatment. Notably, Piwil4 upregulation was not observed in an ERpositive but nontumorigenic breast cancer cell line, MCF12A. In addition, the induced expression of Piwil4 was dependent on estrogen/ERα signaling. To explore the biological significance of Piwil4 in breast cancer growth, we knocked down Piwil4 with multiple siRNAs and observed the suppressed expression of some canonical targets of ER. The knockdown of Piwil4 expression also decreased the migration and invasion capabilities of MCF7 cells. Furthermore, the lossoffunction of Piwil4 reduced the motility of MCF7 cells in woundhealing assays, which could be associated to decreased expression of vimentin and Ncadherin. Collectively, these findings revealed that Piwil4 is a novel regulator of ER signaling that could be targeted to inhibit breast cancer growth and migration.
Asunto(s)
Proteínas Argonautas/genética , Neoplasias de la Mama/genética , Estradiol/farmacología , Receptores de Estrógenos/genética , Neoplasias de la Mama/metabolismo , Neoplasias de la Mama/patología , Movimiento Celular/genética , Proliferación Celular/efectos de los fármacos , Femenino , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Técnicas de Silenciamiento del Gen , Humanos , Células MCF-7 , Proteínas de Unión al ARN , Transducción de Señal/genética , Activación Transcripcional/efectos de los fármacosRESUMEN
Reactive oxygen species (ROS) play important roles in fundamental cellular processes such as proliferation and survival. Here we investigated the effect of oxidative stress on stem cell maintenance and neuronal differentiation in a human embryonic stem cell (hESC) model, Ntera2 (NT2). CM-H2DCFDA and DHE assays confirmed that the oxidizing agent paraquat could induce a high level of ROS in NT2 cells. Quantitative PCR, Western blotting and immunocytochemistry showed that paraquat-induced oxidative stress suppressed the expression of stemness markers, including NANOG, OCT4 and TDGF1, whereas it enhanced the spontaneous expression of neuronal differentiation markers such as PAX6, NEUROD1, HOXA1, NCAM, GFRA1 and TUJ1. The treated cells even exhibited a strikingly different morphology from control cells, extending out long neurite-like processes. The neurogenic effect of ROS on stem cell behaviour was confirmed by the observations that the expression of neuronal markers in the paraquat-treated cells was suppressed by an antioxidant while further enhanced by knocking down Nrf2, a key transcription factor associated with antioxidant signaling. Lastly, paraquat dose-dependently activated the neurogenic MAPK-ERK1/2, which can be reversed by the MEK1/2 inhibitor SL327. Our study suggests that excessive intracellular ROS can trigger the exit from stem cell state and promote the neuronal differentiation of hESCs, and that MAPK-ERK1/2 signaling may play a proactive role in the ROS-induced neuronal differentiation of hESCs.