Figure 4. Zinc reactivates the HIF-1α-inhibited HIPK2/p53 signalling. (A) Immunoblot of RKO cells in which the effect of HIPK2 overexpression on p53Ser46 phosphorylation was abolished by HIF-1α co-expression and restored by concomitant zinc (100 μm for 24 h) treatment. (B) Luciferase assay in RKO cells stable transfected with p53AIP1-luc reporter showing that the HIPK2-induced luciferase activity was inhibited by HIF-1α and rescued by zinc treatment (100 μm for 24 h); zinc did not rescued the HIPK2 inhibition triggered by the HIF-1αP/A mutant and the HIF-1αDNA mutant did not inhibit HIPK2-induced transcriptional activity. Results represent mean ± s.d. from three experiments. (C) Lysates from RKO cells treated as indicated were assayed for RT-PCR analyses of p53 apoptotic target Noxa. GAPDH is a loading control. (D) Tunel assay of RKO cells showing that the HIPK2-induced apoptotic cell death was significantly inhibited by HIF-1α and strongly rescued by zinc treatment. *P=0.001.