RESUMEN
INTRODUCTION: Signal transducer and activator of transcription (STAT) 5b is a transcription factor involved in pro-proliferative and pro-survival signaling in a number of solid tumors, including breast cancer. The contribution of STAT5b to breast cancer cell motility has not been explored. This work aims to elucidate the role of STAT5b in breast cancer cell migration. METHODS: STAT5b was knocked down by using siRNA in two aggressive, highly migratory breast cancer cell lines (BT-549 and MDA-MB-231), and transwell migration assays were performed to determine the importance of STAT5b for their migration. Knockdown-rescue experiments were used to validate the specificity of STAT5b knockdown and to determine which regions/functions of STAT5b are necessary for its role in migration. Live-cell imaging of wound healing and spreading was carried out to examine cell morphology and motility after STAT5b knockdown. RESULTS: Knockdown of STAT5b, but not STAT5a, inhibited migration of BT-549 and MDA-MB-231 breast cancer cells to serum by 60% to 80%, and inhibited migration equally over a range of serum concentrations (0.1% to 10% serum). Migratory inhibition upon STAT5b knockdown could be rescued by reintroduction of wild-type STAT5b, as well as Y699F- and dominant-negative STAT5b mutants, but not an SH2 domain defective R618K-STAT5b mutant. beta1- integrin-mediated migration of breast cancer cells to fibronectin was inhibited with STAT5b knockdown, and loss of STAT5b correlated with loss of directional migration and formation of multiple, highly contractile protrusions upon attachment to fibronectin. CONCLUSIONS: The data presented here demonstrate that STAT5b is integral to breast cancer cell migration and identify a novel, SH2-dependent function of STAT5b in regulating beta1-integrin-mediated migration of highly aggressive breast cancer cells.
Asunto(s)
Neoplasias de la Mama/patología , Integrina beta1/fisiología , Invasividad Neoplásica/fisiopatología , Proteínas de Neoplasias/fisiología , Factor de Transcripción STAT5/fisiología , Línea Celular Tumoral/efectos de los fármacos , Línea Celular Tumoral/patología , Movimiento Celular/fisiología , Femenino , Fibronectinas/farmacología , Técnicas de Silenciamiento del Gen , Humanos , Proteínas de Neoplasias/química , Interferencia de ARN , ARN Interferente Pequeño/farmacología , Factor de Transcripción STAT5/química , Factor de Transcripción STAT5/genética , Cicatrización de Heridas , Dominios Homologos srcRESUMEN
17beta-Estradiol (E2) acts through the estrogen receptor alpha (ERalpha) to stimulate breast cancer proliferation. Here, we investigated the functional relationship between ERalpha and signal transducer and activator of transcription (STAT)5b activity in ER+ MCF-7 and T47D human breast cancer cells after specific knockdown of STAT5b. STAT5b small interfering RNA (siRNA) inhibited E2-induced bromodeoxyuridine (BrdU) incorporation in both cell lines, as well as the E2-induced increase in MCF-7 cell number, cyclin D1 and c-myc mRNA, and cyclin D1 protein expression, indicating that STAT5b is required for E2-stimulated breast cancer proliferation. E2 treatment stimulated STAT5b tyrosine phosphorylation at the activating tyrosine Y699, resulting in increased STAT5-mediated transcriptional activity, which was inhibited by a Y669F STAT5b mutant. E2-induced STAT5-mediated transcriptional activity was inhibited by overexpressing a kinase-defective epidermal growth factor receptor (EGFR), or the EGFR tyrosine kinase inhibitor tyrphostin AG1478, indicating a requirement for EGFR kinase activity. Both E2-induced STAT5b tyrosine phosphorylation and STAT5-mediated transcription were also inhibited by the ER antagonist ICI 182,780 and the c-Src inhibitor PP2, indicating additional requirements for the ER and c-Src kinase activity. EGFR and c-Src kinase activities were also required for E2-induced cyclin D1 and c-myc mRNA. Together, these studies demonstrate positive cross talk between ER, c-Src, EGFR, and STAT5b in ER+ breast cancer cells. Increased EGFR and c-Src signaling is associated with tamoxifen resistance in ER+ breast cancer cells. Here we show that constitutively active STAT5b not only increased basal DNA synthesis, but also conferred tamoxifen resistance. Because STAT5b plays an integral role in E2-stimulated proliferation and tamoxifen resistance, it may be an effective therapeutic target in ER+ breast tumors.
Asunto(s)
Neoplasias de la Mama/enzimología , Receptores ErbB/metabolismo , Estradiol/farmacología , Receptor alfa de Estrógeno/metabolismo , Proteínas Proto-Oncogénicas pp60(c-src)/metabolismo , Factor de Transcripción STAT5/metabolismo , Transducción de Señal/efectos de los fármacos , Neoplasias de la Mama/genética , Neoplasias de la Mama/patología , Recuento de Células , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Ciclina D1/metabolismo , Resistencia a Antineoplásicos/efectos de los fármacos , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Genes Relacionados con las Neoplasias , Humanos , Fosforilación/efectos de los fármacos , Fosfotirosina/metabolismo , Factor de Transcripción STAT5/genética , Tamoxifeno/farmacología , Transcripción Genética/efectos de los fármacosRESUMEN
Shroom is an actin-associated determinant of cell morphology that is required for neural tube closure in both mice and frogs. Shroom regulates this process by causing apical constriction of epithelial cells via a pathway involving myosin II. Here we report on characterization of the Shroom-related proteins Apxl and KIAA1202 and their role in cell architecture. Shroom, Apxl, and KIAA1202 exhibit differing abilities to interact with the actin cytoskeleton. In fibroblasts, Shroom readily associates with actin stress fibers and induces bundling, Apxl is found on cortical actin, and KIAA1202 is localized to a cytoplasmic population of F-actin. In epithelial cells, Apxl and KIAA1202 do not induce apical constriction as Shroom does, but have the capacity to do so if targeted to the apical junctional complex. To determine whether the activity of Shroom-like proteins is conserved in invertebrates, we have tested the ability of the lone Shroomrelated protein in Drosophila, CG8603, to activate the constriction pathway. A chimeric protein consisting of the Shroom targeting domain and the Drosophila protein elicits constriction. Finally, we show that Apxl is involved in regulating the cytoskeletal organization and architecture of endothelial cells. We predict that the ability of Shroom-like proteins to regulate cellular morphology is conserved in evolution and is regulated in part by subcellular localization.