Exposure of cells to Ni(II), but not Cr(VI), stimulates HIF-dependent transcription. A, Time-course of HIF-dependent transcription induced by Ni(II) or Cr(VI) in 1HAEo- cells. 1HAEo- cells were transfected with HRE-Luc reporter plasmid and incubated with 5 μM CrCl3, 5 μM K2CrO4 or 0.25 mM NiSO4 for various time periods shown in the Figure. Relative luciferase activity was detected and expressed as the fold increase over control. Data are presented as mean values ± SD. B, Induction of NDRG1/Cap43 or CA9 proteins by various concentrations of Cr(VI) or 0.5 mM NiSO4. 1HAEo- cells were exposed to metals for 20 h. Total cell extracts were prepared for immunoblotting and probed with antibodies directed against NDRG1/Cap43 or CA9 proteins. The same blot was probed with antibodies against β-actin to provide loading control.