RESUMEN
BACKGROUND: Colorectal cancer (CRC) is characterised by hypoxia, which activates gene transcription through hypoxia-inducible factors (HIF), as well as by expression of epidermal growth factor (EGF) and EGF receptors, targeting of which has been demonstrated to provide therapeutic benefit in CRC. Although EGF has been demonstrated to induce expression of angiogenic mediators, potential interactions in CRC between EGF-mediated signalling and the hypoxia/HIF pathway remain uncharacterised. METHODS: PCR-based profiling was applied to identify angiogenic genes in Caco-2 CRC cells regulated by hypoxia, the hypoxia mimetic dimethyloxallylglycine (DMOG) and/or EGF. Western blotting was used to determine the role of HIF-1alpha, HIF-2alpha and MAPK cell signalling in mediating the angiogenic responses. RESULTS: We identified a total of 9 angiogenic genes, including angiopoietin-like (ANGPTL) 4, ephrin (EFNA) 3, transforming growth factor (TGF) ß1 and vascular endothelial growth factor (VEGF), to be upregulated in a HIF dependent manner in Caco-2 CRC cells in response to both hypoxia and the hypoxia mimetic dimethyloxallylglycine (DMOG). Stimulation with EGF resulted in EGFR tyrosine autophosphorylation, activation of p42/p44 MAP kinases and stabilisation of HIF-1α and HIF-2α proteins. However, expression of 84 angiogenic genes remained unchanged in response to EGF alone. Crucially, addition of DMOG in combination with EGF significantly increased expression of a further 11 genes (in addition to the 9 genes upregulated in response to either DMOG alone or hypoxia alone). These additional genes included chemokines (CCL-11/eotaxin-1 and interleukin-8), collagen type IV α3 chain, integrin ß3 chain, TGFα and VEGF receptor KDR. CONCLUSION: These findings suggest that although EGFR phosphorylation activates the MAP kinase signalling and promotes HIF stabilisation in CRC, this alone is not sufficient to induce angiogenic gene expression. In contrast, HIF activation downstream of hypoxia/DMOG drives expression of genes such as ANGPTL4, EFNA3, TGFß1 and VEGF. Finally, HIF activation synergises with EGF-mediated signalling to additionally induce a unique sub-group of candidate angiogenic genes. Our data highlight the complex interrelationship between tumour hypoxia, EGF and angiogenesis in the pathogenesis of CRC.
Asunto(s)
Neoplasias Colorrectales/genética , Neoplasias Colorrectales/patología , Factor de Crecimiento Epidérmico/farmacología , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Hipoxia/genética , Neovascularización Patológica/genética , Transcriptoma , Hipoxia de la Célula , Línea Celular Tumoral , Neoplasias Colorrectales/metabolismo , Receptores ErbB/metabolismo , Humanos , Factor 1 Inducible por Hipoxia/metabolismo , Neovascularización Patológica/metabolismoRESUMEN
The paradigm of a therapy aimed at inhibiting the formation of blood vessels, which would consequentially deprive cells and tissues of oxygen and nutrients, was born from the concept pioneered by the late Judah Folkman that blood vessel formation is central to the progression and maintenance of diseases which involve cellular metabolism and tissue expansion, and cancer in particular. The prototype targeted angiogenesis inhibitor anti-vascular endothelial growth factor (VEGF) antibody bevacizumab was approved in 2004 for colorectal cancer, and has since been approved for other cancers. Rheumatoid arthritis (RA) is a chronic inflammatory disease, during which inflamed tissue invades and destroys cartilage and bone. The tissue expansion, invasion, expression of cytokines and growth factors and areas of hypoxia which are a feature of RA have resulted in the hypothesis that angiogenesis inhibition may also be beneficial in RA, drawing on the success of bevacizumab. This review focuses on our current understanding of the importance of angiogenesis in RA, and on the lessons which may be learnt from the clinical experiences of angiogenesis blockade, particularly in colorectal cancer.