As we all known hypoxia is a hallmark of tumour
As we all known, hypoxia is a hallmark of tumour microenvironment, which is a key regulator of tumour growth and metastasis . Hypoxia meditates a series of cellular responses including angiogenesis by activating transcriptional factor hypoxia inducible factor (HIF), which is consist of an obligate dimer of HIF-1α and HIF-1βsubunits, 2 isoforms (HIF-1α and HIF-2α). HIF-1αoverexpression is associated with tumour invasion, liver metastasis  as well as poor prognosis  in colorectal cancer (CRC), which upregualtes several angiogenic genes, and then induces angiogenesis , , . However, whether exsist other genes that been regulated by HIF-1α need to be verified, then provide new targets for cancer therapy.
Materials and methods
Discussion Hypoxia is a common feature in human cancers, when tumour grow beyound 2–3 mm3 in size, the tumour growth would be restricted due to without neo-vasculation  and the tumour would be in hypoxia microenvironment. Under the condition, the tumour would trigger the angiogenesis switch for survival, and increase the ability of cancer sglt-2 to invade and metastasis. However, hypoxia regulated genes that invovled angiogenesis in CRC have not been explored in detail. Therefore, the identification of vascular genes in hypoxia condition could provide new targets for therapeutic intervention. In the present study, we found that chronic hypoxia could increase the ability of HUVEC tube formation and promote colorctal cancer cells invasion. Using microarrays and the DAVID bioinformatics database and validated by RT-qPCR, we identified several genes and pathways that associated with angiogenesis, these results might identify more reasonable target candidates for colorectal cancer anti-angiogeneic therapy in the future. As we known, Angiogenesis is essential for the growth of tumour and metastasis of cancer cells. It has been reported that acute hypoxia promotes tumour cell migration and invasion , , , endothelial cells tube formation , however, to date, there are a few studies investigating the role of chronic hypoxia on the invasive phenotype . The difference between acute and chronic hypoxia is not only represent pathophsiologies, but also variable biological and therapeutical consequences , , Therefore, It is vital to distinguish between them. In the present study, we used the conditional medium from CRC cells under prolonged hypoxia (72 h) to determine whether chronic hypoxia modulate endothelial cell tube formation, in addition, we performed invasion assay to determine wether chronic hypoxia modulate cancer cell invasion. We found that endothelial cells cultured with CM from HCT-116 cells under chronic hypoxia condition increased the tube formation capacity, and chronic hypoxia promoted invasion of CRC cells (Fig. 1). On the basis of this analysis, bioinformatics analysis was performed to investigate the different expressed genes that may invovled in angiogenesis under chronic hypoxia condition, biological process annotation of these genes revealed that 27 of these genes were implicated in blood vessel development, vasculature development, blood vessel morphogenesis, angiogenesis (Fig. 2B), and gene/gene-protein/gene interaction analysis indicated that 17 genes/proteins strongly interacted with each other (Fig. 2C–F), we selected nine genes for further analysis, as mention above, because of the difference of acute and chronic hypoxia, these genes (VEGF-A, Smad7, Jun, IL-8, CXCR-4, PDGF-A, CD44, TGF-A, ANGPTL-4) expression levels were confirmed by RT-qPCR under 24 h, 72 h hypoxia condition compared with nomoxia condition. We explored the difference of these genes with increase of hypoxia time, as shown in Fig. 3, VEGF-A, IL-8, ANGPTL-4 expression levels decreased with the time goes, these may be the results of tumour cell adaption, however, even under chronic hypoxia (72 h), the expression level of these genes was higher than nomoxia condition, these results explained the reason why chronic hypoxia increased the tumour cell invasive phenotype as shown in Fig. 1 of these genes, VEGF-A, IL-8, CXCR-4 is known to be regulated by hypoxia in other cells and have been confirmed which can promote metastasis , , . TGF-α, an EGFR ligand, selectively binds to EGFR and activated EGFR-mediated signaling pathway, which regulate cell proliferation, differentiation, cell motility and survival . Chang et al.  demonstrated that protease-activated receptor-2 (PAR-2) promote angiogenesis through up-regulated hypoxia-inducible factor 1α(HIF-1α) and HIF-2α then activated TGF-α transcription in pancreatic cancer. Khong et al. identified hypoxia-regulated ANGPTL-4, EFNA3, TGFβ1, VEGF genes in colorectal cancer . ANGPTL-4, angiopoietin like protein-4, which palys complex and often contradictory roles in vascular biology and tumour metastasis , , . It was reported to be regulated by HIF-1α and promoted metastasis in hepatocellular carcinoma , in addition, a study reported that expression of ANGPTL-4 correlates with the depth of tumour invasion, venous invasion, and Duck\'s stage in CRC . Smad7 is an inhibitor of transforming growth factor βactivated siganling pathway, which has been reported up regulated and activated invasion under hypoxia condition in several cancers , moreover, a study showed that smad7 paly a important role in sustain colon tumorigenesis . Jun and its upstream proteins JNK have long been considered to be associated with angiogenesis, when c-jun was suppressed in human endothelial cells, the cells no longer form new blood vessels in vivo and in vitro . Together, these results indicate that the genes identified in this study might play crucial role in CRC metastasis, probably functioning as a group.