AIM: To study the expression of carbonic anhydrase(CA) 9 in human hepatocellular carcinoma(HCC) cells.METHODS: We studied CA9 protein, CA9 m RNA and hypoxia-inducible factor-1 alpha(HIF-1α) protein levels in Hep3 B cells exposed in different parallel approaches. In one of these approaches, HCC cells were exposed to extreme in vitro hypoxia(24 h 0.1% O2) without or with interleukin(IL)-1, IL-6, tumor necrosis factoralpha(TNF-α) and transforming growth factor-beta(TGF-β) stimulation for the same hypoxic exposure time or exposed to normoxic oxygenation conditions without or with cytokine stimulation.RESULTS: The tumour cell line analysed showed a strong hypoxic CA9 m RNA expression pattern in response to prolonged severe hypoxia with cell-line specific patterns and a marked induction of CA9 protein in response to severe hypoxia. These results were paralleled by the results for HIF-1α protein under identical oxygenation conditions with a similar expression tendency to that displayed during the CA9 protein expression experimental series. Continuous stimulation with the cytokines, IL-1, IL-6, TNF-α and TGF-β, under normoxic conditions significantly increased the carbonic anhydrase 9 expression level at both the protein and m RNA level, almost doubling the CA9 m RNA and CA9 and HIF-1α protein expression levels found under hypoxia. The findings from these experiments indicated that hypoxia is a positive regulator of CA9 expression in HCC, and the four signal transduction pathways, IL-1, IL-6, TNF-α and TGF-β, positively influence CA9 expression under both normoxic and hypoxic conditions.CONCLUSION: These findings may potentially be considered in the design of anti- cancer therapeutic approaches involving hypoxia-induced or cytokine stimulatory effects on expression. In addition, they provideevidence of the stimulatory role of the examined cytokine families resulting in an increase in CA9 expression under different oxygenation conditions in human cancer, especially HCC, and on the role of the CA9 gene as a positive disease regulator in human cancer. AIM: To study the expression of carbonic anhydrase (CA) 9 in human hepatocellular carcinoma (HCC) cells. METHODS: We studied CA9 protein, CA9 m RNA and hypoxia-inducible factor- 1 alpha (HIF- lα) protein levels in Hep3 B In one of these approaches, HCC cells were exposed to extreme in vitro hypoxia (24 h 0.1% O2) without or with interleukin (IL) -1, IL-6, tumor necrosis factoralpha ) and transforming growth factor-beta (TGF-β) stimulation for the same hypoxic exposure time or exposed to normoxic oxygenation conditions without or with cytokine stimulation. The tumor cell line was analyzed to show strong hypoxic CA9 m RNA expression pattern in response to prolonged severe hypoxia with cell-line specific patterns and a marked induction of CA9 protein in response to severe hypoxia. These results were paralleled by the results for HIF-1α protein under identical oxygenation conditions with a similar expression tendency to that displayed du cyclic the CA9 protein expression experimental series. Continuous stimulation with the cytokines, IL-1, IL-6, TNF-α and TGF-β, under normoxic conditions significantly increased the carbonic anhydrase 9 expression level at both the protein and m RNA level, The findings from these experiments indicate that hypoxia is a positive regulator of CA9 expression in HCC, and the four signal transduction pathways, IL-1, IL- 6, TNF-α and TGF-β, positively influence CA9 expression under both normoxic and hypoxic conditions. CONCLUSION: These findings may potentially be considered in the design of anti- cancer of vascular approaches involving hypoxia-induced or cytokine stimulatory effects on expression. In addition, they provideevidence of the stimulatory role of the examined cytokine families resulting in an increase in CA9 expression under different oxygenation conditions in human cancer, especially HCC, andon the role of the CA9 gene as a positive disease regulator in human cancer.