The large decrease in EGR1 levels during GSC differentiation shown by both microarray (Fig. 4b) and by western blot (Fig. 2d) and the significant positive correlation between KLF4 and EGR1 gene expression levels in clinical GBM samples led us to examine the relationship between EGR1 and KLF4 protein levels. Here, KLF4 is linked to glioblastoma.