RESUMEN
Human pituitary tumour-transforming gene 1 (hPTTG1) is an oncogenic transcription factor that is overexpressed in many tumour types, especially tumours with metastatic abilities. However, how hPTTG1 overexpression drives metastasis is not yet clear. As a transcription factor, hPTTG1 may promote metastasis by activating target genes that are involved in the metastatic process. Here, we showed that Rho guanine nucleotide exchange factor-H1 (GEF-H1) was transcriptionally activated by hPTTG1, thereby promoting breast cancer metastasis. Luciferase reporter analyses and chromatin immunoprecipitation (ChIP) assays showed that hPTTG1 directly bound and activated the GEF-H1 gene promoter. In this study, RNA interference-mediated knockdown of hPTTG1 in highly metastatic breast tumour cells decreased GEF-H1 expression and RhoA activation, thereby reducing cell motility and invasion, and interfering with cytoskeletal remodelling in vitro, and impairing the tumour metastasis in vivo. The restoration of GEF-H1 expression in hPTTG1-knockdown cells rescued the hPTTG1-knockdown effects on cytoskeletal changes in vitro and tumour metastasis in vivo. Conversely, ectopic expression of hPTTG1 in non-metastatic breast tumour cells induced cytoskeletal rearrangements, and allowed these cells to metastasise in a mouse model by orthotopic implantation. In human tumour samples, hPTTG1 expression was also correlated to GEF-H1 expression in aggressive breast carcinoma. Altogether, these findings definitively establish a role for hPTTG1 in activating the GEF-H1/RhoA pathway as a newly identified mechanism in breast cancer metastasis.
Asunto(s)
Neoplasias de la Mama/metabolismo , Carcinoma/metabolismo , Factores de Intercambio de Guanina Nucleótido/metabolismo , Metástasis de la Neoplasia/patología , Proteínas de Neoplasias/metabolismo , Transducción de Señal , Proteína de Unión al GTP rhoA/metabolismo , Neoplasias de la Mama/patología , Carcinoma/patología , Femenino , Humanos , Invasividad Neoplásica , Factores de Intercambio de Guanina Nucleótido Rho , SecurinaRESUMEN
A 41-year-old woman presented with dyspnoea, persistent leucocytosis and eosinophilia for 8 months. High-resolution computed tomography scan and pathology of bronchoalveolar lavage confirmed the diagnosis of hypereosinophilic pneumonitis. The patient was treated with prednisolone (0·5-1 mg/kg/day) for more than 20 weeks under the impression of hypereosinophilic syndrome, but without improvement of leucocytosis and eosinophilia. The bone marrow aspiration smear disclosed hypercellular marrow with myeloid hyperplasia and eosinophilia. The fusion gene detection was positive for KIAA1509-PDGFRß. Myeloid neoplasm associated with eosinophilia and abnormality of PDGFRß was then diagnosed (Tefferi A, Vardiman JW, Leukemia, 22, 2008, 14). The tyrosine kinase inhibitor, imatinib mesylate (Glivec; 200 mg/day), was administered along with prednisolone (0·25-1 mg/kg/day). White blood cell (WBC) count decreased from 49,500/µL to 17,200/µL, and eosinophil count decreased from 1932/µL to 35/µL, which represent percentage dropped from 7·7%> to 0·2%. Withdrawal of prednisolone was done to avoid adverse events. However, absolute eosinophil count increased progressively despite the continue administration of imatinib and negative detection PDGFRß fusion gene. The patient then received combination therapy of imatinib and prednisolone again. WBC and absolute eosinophil were normalized subsequently. We had discontinued the prednisolone one more time, and rebound of eosinophilia was seen again. The phenomenon of rebounding of eosinophilia was observed in two subsequent withdrawals of prednisolone. Either steroid or imatinib mesylate alone failed to achieve complete haematological response. A synergistic effect of imatinib and steroid is postulated.