ABSTRACT
Inhibition of VEGF signaling leads to a proinvasive phenotype in mouse models of glioblastoma multiforme (GBM) and in a subset of GBM patients treated with bevacizumab. Here, we demonstrate that vascular endothelial growth factor (VEGF) directly and negatively regulates tumor cell invasion through enhanced recruitment of the protein tyrosine phosphatase 1B (PTP1B) to a MET/VEGFR2 heterocomplex, thereby suppressing HGF-dependent MET phosphorylation and tumor cell migration. Consequently, VEGF blockade restores and increases MET activity in GBM cells in a hypoxia-independent manner, while inducing a program reminiscent of epithelial-to-mesenchymal transition highlighted by a T-cadherin to N-cadherin switch and enhanced mesenchymal features. Inhibition of MET in GBM mouse models blocks mesenchymal transition and invasion provoked by VEGF ablation, resulting in substantial survival benefit.
Subject(s)
Brain Neoplasms/pathology , Epithelial-Mesenchymal Transition/physiology , Glioblastoma/pathology , Proto-Oncogene Proteins c-met/metabolism , Vascular Endothelial Growth Factor A/physiology , Vascular Endothelial Growth Factor Receptor-2/metabolism , Antibodies, Monoclonal, Humanized/pharmacology , Antibodies, Monoclonal, Humanized/therapeutic use , Bevacizumab , Brain Neoplasms/drug therapy , Brain Neoplasms/metabolism , Glioblastoma/drug therapy , Glioblastoma/metabolism , Humans , Phosphorylation , Proto-Oncogene Proteins c-met/genetics , Signal Transduction , Vascular Endothelial Growth Factor A/antagonists & inhibitors , Vascular Endothelial Growth Factor A/metabolismABSTRACT
OBJECTIVE: Forkhead box O (FoxO) transcription factors represent evolutionarily conserved targets of insulin signaling, regulating metabolism and cellular differentiation in response to changes in nutrient availability. Although the FoxO1 isoform is known to play a key role in adipogenesis, its physiological role in differentiated adipose tissue remains unclear. RESEARCH DESIGN AND METHODS: In this study, we analyzed the phenotype of FoxO1 haploinsufficient mice to investigate the role of FoxO1 in high-fat diet-induced obesity and adipose tissue metabolism. RESULTS: We showed that reduced FoxO1 expression protects mice against obesity-related insulin resistance with marked improvement not only in hepatic insulin sensitivity but also in skeletal muscle insulin action. FoxO1 haploinsufficiency also resulted in increased peroxisome proliferator-activated receptor (PPAR)gamma gene expression in adipose tissue, with enhanced expression of PPARgamma target genes known to influence metabolism. Moreover, treatment of mice with the PPARgamma agonist rosiglitazone caused a greater improvement in in vivo insulin sensitivity in FoxO1 haploinsufficient animals, including reductions in circulating proinflammatory cytokines. CONCLUSIONS: These findings indicate that FoxO1 proteins negatively regulate insulin action and that their effect may be explained, at least in part, by inhibition of PPARgamma function.