RESUMO
Malignant glioblastomas are characterized by their ability to infiltrate into normal brain. We previously reported that binding of the multifunctional cytokine TNF-like weak inducer of apoptosis (TWEAK) to its receptor fibroblast growth factor-inducible 14 (Fn14) induces glioblastoma cell invasion via Rac1 activation. Here, we show that Cdc42 plays an essential role in Fn14-mediated activation of Rac1. TWEAK-treated glioma cells display an increased activation of Cdc42, and depletion of Cdc42 using siRNA abolishes TWEAK-induced Rac1 activation and abrogates glioma cell migration and invasion. In contrast, Rac1 depletion does not affect Cdc42 activation by Fn14, showing that Cdc42 mediates TWEAK-stimulated Rac1 activation. Furthermore, we identified two guanine nucleotide exchange factors (GEF), Ect2 and Trio, involved in TWEAK-induced activation of Cdc42 and Rac1, respectively. Depletion of Ect2 abrogates both TWEAK-induced Cdc42 and Rac1 activation, as well as subsequent TWEAK-Fn14-directed glioma cell migration and invasion. In contrast, Trio depletion inhibits TWEAK-induced Rac1 activation but not TWEAK-induced Cdc42 activation. Finally, inappropriate expression of Fn14 or Ect2 in mouse astrocytes in vivo using an RCAS vector system for glial-specific gene transfer in G-tva transgenic mice induces astrocyte migration within the brain, corroborating the in vitro importance of the TWEAK-Fn14 signaling cascade in glioblastoma invasion. Our results suggest that the TWEAK-Fn14 signaling axis stimulates glioma cell migration and invasion through two GEF-GTPase signaling units, Ect2-Cdc42 and Trio-Rac1. Components of the Fn14-Rho GEF-Rho GTPase signaling pathway present innovative drug targets for glioma therapy.
Assuntos
Glioblastoma , Proteínas Proto-Oncogênicas , Receptores do Fator de Necrose Tumoral , Proteína cdc42 de Ligação ao GTP , Animais , Astrocitoma/genética , Astrocitoma/metabolismo , Movimento Celular/genética , Citocina TWEAK , Glioblastoma/genética , Glioblastoma/metabolismo , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Humanos , Camundongos , Invasividade Neoplásica/genética , Neuropeptídeos/metabolismo , Fosfoproteínas/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/metabolismo , Receptores do Fator de Necrose Tumoral/genética , Receptores do Fator de Necrose Tumoral/metabolismo , Transdução de Sinais , Receptor de TWEAK , Fatores de Necrose Tumoral/farmacologia , Proteína cdc42 de Ligação ao GTP/genética , Proteína cdc42 de Ligação ao GTP/metabolismo , Proteínas rac de Ligação ao GTP/metabolismo , Proteínas rac1 de Ligação ao GTPRESUMO
A critical problem in the treatment of malignant gliomas is the extensive infiltration of individual tumor cells into adjacent brain tissues. This invasive phenotype severely limits all current therapies, and to date, no treatment is available to control the spread of this disease. Members of the tumor necrosis factor (TNF) ligand superfamily and their cognate receptors regulate various cellular responses including proliferation, migration, differentiation, and apoptosis. Specifically, the TNFRSF19/TROY gene encodes a type I cell surface receptor that is expressed on migrating or proliferating progenitor cells of the hippocampus, thalamus, and cerebral cortex. Here, we show that levels of TROY mRNA expression directly correlate with increasing glial tumor grade. Among malignant gliomas, TROY expression correlates inversely with overall patient survival. In addition, we show that TROY overexpression in glioma cells activates Rac1 signaling in a Pyk2-dependent manner to drive glioma cell invasion and migration. Pyk2 coimmunoprecipitates with the TROY receptor, and depletion of Pyk2 expression by short hairpin RNA interference oligonucleotides inhibits TROY-induced Rac1 activation and subsequent cellular migration. These findings position aberrant expression and/or signaling by TROY as a contributor, and possibly as a driver, of the malignant dispersion of glioma cells.
Assuntos
Neoplasias Encefálicas/metabolismo , Quinase 2 de Adesão Focal/metabolismo , Glioblastoma/metabolismo , Receptores do Fator de Necrose Tumoral/biossíntese , Proteínas rac1 de Ligação ao GTP/metabolismo , Animais , Neoplasias Encefálicas/genética , Neoplasias Encefálicas/patologia , Linhagem Celular Tumoral , Movimento Celular/fisiologia , Quinase 2 de Adesão Focal/deficiência , Regulação Neoplásica da Expressão Gênica , Glioblastoma/genética , Glioblastoma/patologia , Humanos , Imunoprecipitação , Invasividade Neoplásica , RNA Mensageiro/biossíntese , RNA Mensageiro/genética , RNA Interferente Pequeno/administração & dosagem , RNA Interferente Pequeno/genética , Ratos , Ratos Wistar , Receptores do Fator de Necrose Tumoral/antagonistas & inibidores , Receptores do Fator de Necrose Tumoral/genética , Receptores do Fator de Necrose Tumoral/metabolismo , Transfecção , Proteínas rac1 de Ligação ao GTP/deficiênciaRESUMO
Malignant gliomas are the most common primary brain tumors. Despite intensive clinical investigation and significant technical advances in surgical and radiation treatment, the impact on clinical outcome for patients with malignant gliomas is disappointing. We have previously shown that tumor necrosis factor-like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor superfamily, can stimulate glioma cell survival via binding to the Fn14 receptor, activation of the NF-kappaB pathway, and upregulation of BCL-X(L) gene expression. Here, we show that TWEAK treatment of glioma cells leads to phosphorylation of Akt and BAD. TWEAK stimulation results in the phosphorylation of both Akt1 and Akt2. However, small interfering RNA (siRNA)-mediated depletion of either Akt1 or Akt2 showed that BAD serine 136 phosphorylation is dependent specifically on Akt2 function. Depletion of Akt2 expression by siRNA also abrogates TWEAK-stimulated glioma cell survival, whereas no effect on glioma cell survival was observed after siRNA-mediated depletion of Akt1 expression. Surprisingly, although siRNA-mediated depletion of BAD in glioma cells abrogates cytotoxic- and chemotherapy-induced apoptosis, TWEAK still displays a strong protective effect, suggesting that BAD serine 136 phosphorylation plays a minor role in TWEAK-Akt2-induced glioma cell survival. We also report here that AKT2 gene expression levels increased with glioma grade and inversely correlate with patient survival. Additionally, immunohistochemical analysis showed that Akt2 expression positively correlates with Fn14 expression in glioblastoma multiforme specimens. We hypothesize that the TWEAK-Fn14 signaling axis functions, in part, to enhance glioblastoma cell survival by activation of the Akt2 serine/threonine protein kinase.