Comment on the role of FIH in the inhibitory effect of bortezomib on hypoxia-inducible factor-1.

Recently, Shin et al reported that the proteasomal inhibitor bortezomib inhibits the hypoxic response by stimulating the factor-inhibiting HIF-1 (FIH)–mediated repression of hypoxiainducible factor-1 (HIF-1).1 The essence of this study is that bortezomib enhances the FIH function and the repression is dependent on asparagine 803 (N803). Both conclusions are in contradiction to previously published data,2,3 Shin et al suggested that this contradiction could be the consequence of a cell-type specific effect and/or the higher concentrations of bortezomib used in these previous studies. We tested the effect of various concentrations of bortezomib on the activity of the wild type and N803A mutant Gal4 HIF-1 C-terminal activation domain (CAD) in various cell lines. No inhibitory effect was observed at subnanomolar concentrations in any of 4 cell lines tested, including the HEK 293 cell line used in the Shin et al studies (data not shown). More importantly, we found that in all 4 cell lines activities of the wild type and the N803A mutant HIF-1 CAD constructs were strictly coregulated by bortezomib (Figure 1). Both constructs were invariably inhibited by higher concentrations ( 10 nM), whereas 1 nM had a moderate