Hypoxia-inducible factor I alpha expression increases during colorectal carcinogenesis and tumor progression

Background: Hypoxia-inducible factor I alpha (HIF-I alpha) is involved in processes promoting carcinogenesis of many tumors. However, its role in the development of colorectal cancer is unknown. To investigate the significance of HIF-I alpha during colorectal carcinogenesis and progression we examined its expression in precursor lesions constituting the conventional and serrated pathways, as well as in non-metastatic and metastatic adenocarcinomas. Methods: Immunohistochemistry and Western blot is used to analyse HIF-I alpha expression in normal colonic mucosa, hyperplastic polyps (HPP), sessile serrated adenomas (SSA), low-grade (TA-LGD) and high-grade (TA-HGD) traditional adenomas as well as in non-metastatic and metastatic colorectal adenocarcinomas. Eight colorectal carcinoma cell lines are tested for their HIF-I alpha inducibility after lipopolysaccharide (LPS) stimulation using western blot and immunocytochemistry. Results: In normal mucosa, HPP and TA-LGD HIF-I alpha was not expressed. In contast, perinuclear protein accumulation and nuclear expression of HIF-I alpha were shown in half of the examined SSA and TA-HGD. In all investigated colorectal carcinomas a significant nuclear HIF-I alpha overexpression compared to the premalignant lesions was observed but a significant correlation with the metastatic status was not found. Nuclear HIF-I alpha expression was strongly accumulated in perinecrotic regions. In these cases HIF-I alpha activation was seen in viable cohesive tumor epithelia surrounding necrosis and in dissociated tumor cells, which subsequently die. Enhanced distribution of HIF-I alpha was also seen in periiflammatory regions. In additional in vitro studies, treatment of diverse colorectal carcinoma cell lines with the potent pro-inflammatory factor lipopolysaccharide (LPS) led to HIF-I alpha expression and nuclear translocation. Conclusion: We conclude that HIF-I alpha expression occurs in early stages of colorectal carcinogenesis and achieves a maximum in the invasive stage independent of the metastatic status. Perinecrotic activation of HIF-I alpha in invasive tumors underlines a dual role of HIF-I alpha by regulating both pro-survival and pro-death processes. HIF-I alpha up-regulation in response to LPS-mediated stimulation and periinflammatory expression in invasive carcinomas suggest its involvement in inflammatory events. These patterns of HIFI alpha inducibility could contribute indirectly to the acquisition of a metastatic phenotype.