Hypoxia-inducible expression of tumor-associated carbonic anhydrases

The transcriptional complex hypoxia-inducible factor-1 (HIF-1) has emerged as an important mediator of gene expression patterns in tumors, although th e range of responding genes is still incompletely defined. Here we show tha t the tnmor-associated carbonic anhydrases (CAs) are tightly regulated by t his system. Both CA9 and CA12 were strongly induced by hypoxia in a range o f tumor cell lines. In renal carcinoma cells that are defective for the von Hippel-Lindau (VHL) tumor suppressor, up-regulation of these CAs is associ ated with loss of regulation by hypoxia, consistent with the critical funct ion of pVHL in the regulation of HIF-1. Further studies of CA9 defined a HI F-1-dependent hypoxia response element in the minimal promoter and demonstr ated that tight regulation by the HIF/ pVHL system was reflected In the pat tern of CA IX expression within tumors. Generalized up-regulation of CA IX in VHL-associated renal cell carcinoma contrasted with focal perinecrotic e xpression in a variety of non-VHL-associated tumors. In comparison with vas cular endothelial growth factor mRNA, expression of CA IX demonstrated a si milar, although more tightly circumscribed, pattern of expression around re gions of necrosis and showed substantial although incomplete overlap with a ctivation of the hypoxia marker pimonidazole. These studies define a new cl ass of HIF-1-responsive gene, the activation of which has implications for the understanding of hypoxic tumor metabolism and which may provide endogen ous markers for tumor hypoxia.