ATF4 mRNA and protein expression do not change upon HIF1α or HIF2α KD in chronic hypoxia in PANC-1 cells. PANC-1 cells were treated with RNAiMAX Lipofectamine reagent and small interfering RNA to transiently KD ATF4, HIF1α or HIF2α. The cells were placed in hypoxia (0.2% oxygen) or normoxia (21% oxygen) for 16 or 48 h. All cells with KD were placed in hypoxia. (A and B) RT-qPCR was conducted to determine ATF4 mRNA levels after (A) 16 and (B) 48 h of hypoxia. Fold changes for RT-qPCR are shown relative to normoxic cells. Error bars represent mean ± SD for n=9. The fold changes were analyzed by one-way ANOVA followed by Bonferroni statistical hypothesis test. (C and D) Western blot analysis was conducted to determine the protein expression levels of ATF4 after (C) 16 or (D) 48 h of hypoxia. Fold changes are shown relative to normoxic cells. Error bars represent the mean ± SD for n=3. Fold changes were analyzed by one-way ANOVA followed by Bonferroni statistical hypothesis test. **P<0.01, ***P<0.001 and ****P<0.0001. ATF4, activating transcription factor 4; HIF, hypoxia-inducible factor; KD, knockdown; RT-qPCR, reverse transcription-quantitative PCR.