Tumor hypoxia has been described to increase the resistance of cancer cells to radiation therapy and chemotherapy. Hypoxia-inducible factor-1a (HIF-1a) is the main transcriptional factor activated by hypoxia and it plays a key role in reprogramming tumor growth. We examined in this study whether cobalt chloride induce HIF-1a in different concentrations. U251 human glioblastoma cell line was incubated at 16 h under normoxia with or without CoCl 2 at 1, 5, 10, 20, 25, 50, 100, 150 and 200 lM

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... ments. In proliferation assay, CoCl 2 have shown an increase in cellular induction between 50 and 200 lM, proportionally. CoCl 2 have also shown at 50 lM the maximum induction effect. In addition, CoCl 2 at 50 lM displayed maximum response at 20,000, 30,000 and 40,000 U251 cells, respectively. In HIF-1 expression assay, CoCl 2 increases HIF-1a gene expression between 50 and 200 lM. Western analysis revealed sharp protein band at 118 KDa which represented the HIF-1a protein with high band density at 50 lM CoCl 2 . The present paper reports the adaptive response of human glioblastoma cells to CoCl 2 , a chemical hypoxia-mimicking agent. The effects of the treatment were evaluated on cell proliferation, and HIF-1a gene expression.