FIG. 7.

Regulation of epidermal stemcell marker expression and keratinocyte proliferation by combinatorial GLI/EGFR signaling. cont, control. (A) Expression of GLI1 in the absence of extracellular stimuli resulted in transcriptional activation of the entire panel of epidermal stem cell markers. Simultaneous activation of EGF signaling (GLI1/EGF) abolished GLI1-mediated induction of stem cell marker genes, while the negative stem cell marker CD71 increased in response to combined GLI1/EGF signaling. (B and C) BrdU incorporation analysis showing that GLI1-induced G₁/S-phase progression of keratinocytes requires activation of EGFR signaling. Mean values of three independent experiments are shown. (D) qRT-PCR analysis of cell cycle progression genes regulated in response to GLI1 either in the absence or presence of EGF and/or gefitinib. Inhibition of EGFR by gefitinib (0.5 μM) prevents GLI1-mediated activation of cell cycle progression genes.