Figure 5. Oxygen availability and regulation of MTHFD2. (A) Representative western blots showing hypoxia inducible factor (HIF)-1α and MTHFD2 protein expression in A549, H1299 and H441 cells after treatment with only 100 μM CoCl2 or combined with 100nM digoxin (C+D), where β-actin was used as loading control. (B) Bright-field images of sphere formed by vector control and MTHFD2-knockdown groups of A549, H1299 and H441 cells and (C) their relative quantified number in the presence or absence of 100 μM CoCl2 for 2 days. *, ** and *** indicate p<0.05, p<0.01 and p<0.001, respectively using one-way ANOVA, compared to vector control group.