CA IX is upregulated in CoCl2-induced hypoxia and associated with cell invasive potential and a poor prognosis of breast cancer

Hypoxia, a common phenomenon during the development of malignant solid tumors including breast cancer, serves to propagate a cascade of molecular pathways triggered by hypoxia-inducible factor-1 alpha (HIF-1 alpha). Carbonic anhydrase IX (CA IX), one of the target genes of HIF-1 alpha, has been reported to be involved in progression of malignant tumors. The objective of this study was to investigate the expression of HIF-1 alpha and CA IX in hypoxia, involvement of CA IX in the regulation of migration and invasion/metastasis and its prognostic significance in breast cancer. We used cobalt chloride (CoCl2) as a hypoxia-mimetic agent and found that the expression of HIF-1 alpha protein, CA IX mRNA and protein, is effectively upregulated, except for HIF-1 alpha mRNA. Data showed that the elevated CA IX expression is closely related to in vitro cell migration and invasion, and the underlying mechanism of this process may be associated with epithelial-mesenchymal transition (EMT). The study of clinical tissue samples also demonstrated that CA IX is an independent prognostic marker that may serve as a useful clinical biomarker for predicting tumor progression and the invasion/metastasis of breast cancer. These results provide further insight into the role of CA IX in tumor progression and put forward further strong evidence as well as new consideration for CA IX target therapy.