Selective Modulation of Hedgehog/GLI Target Gene Expression by Epidermal Growth Factor Signaling in Human Keratinocytes

Abstract

Hedgehog (HH)/GLI signaling plays a critical role in epidermal development and basal cell carcinoma. Here, we provide evidence that epidermal growth factor receptor (EGFR) signaling modulates the target gene expression profile of GLI transcription factors in epidermal cells. Using expression profiling and quantitative reverse transcriptase PCR, we identified a set of 19 genes whose transcription is synergistically induced by GLI1 and parallel EGF treatment. Promoter studies of a subset of GLI/EGF-regulated genes, including the genes encoding interleukin-1 antagonist IL1R2, Jagged 2, cyclin D1, S100A7, and S100A9, suggest convergence of EGFR and HH/GLI signaling at the level of promoters of selected direct GLI target genes. Inhibition of EGFR and MEK/ERK but not of phosphatidylinositol 3-kinase/AKT abrogated synergistic activation of GLI/EGF target genes, showing that EGFR can signal via RAF/MEK/ ERK to cooperate with GLI proteins in selective target gene regulation. Coexpression of the GLI/EGF target IL1R2, EGFR, and activated ERK1/2 in human anagen hair follicles argues for a cooperative role of EGFR and HH/GLI signaling in specifying the fate of outer root sheath (ORS) cells. We also show that EGF treatment neutralizes GLI-mediated induction of epidermal stem cell marker expression and provide evidence that EGFR signaling is essential for GLI-induced cell cycle progression in epidermal cells. The results suggest that EGFR signaling modulates GLI target gene profiles which may play an important regulatory role in ORS specification, hair growth, and possibly cancer.

Cooperation between GLI and JUN enhances transcription of JUN and selected GLI target genes

“…This implies the formation of a transcriptional activation complex enabled by phosphorylation of JUN, which then leads to cooperative activation of GLI/JUN target genes. Because JUN is activated in response to many stimuli such as the EGFR signal that has been shown to induce IL1R2 synergistically with GLI (Kasper et al, 2006b;Aberger F, personal communication), it is tempting to speculate that JUN may act as an integrator of multiple inputs and is modulating the expression of HH/GLI target genes. Furthermore, our results show that JUN is also required for the cell-cycle-promoting activity of GLI in keratinocytes, suggesting that the JUN-GLI interaction may have important consequences for HH-dependent skin tumor formation.…”

“…GLI target gene activation and specificity was shown to be affected by PKCd (Riobo et al, 2006a;Lauth et al, 2007), Akt/ PI3K (Riobo et al, 2006b), RAS/MEK/ERK (Pasca di Magliano et al, 2006;Stecca et al, 2007;Neill et al, 2008) and EGF signaling (Bigelow et al, 2005;Kasper et al, 2006b;Mimeault et al, 2007). However, the integration of different upstream signals by co-activators and other modulators on GLI target gene promoters is still far from clear.…”

Activation of the hedgehog-signaling pathway in human cancer and the clinical implications

“…Recent data further show the significance of IGF signaling for Hh-mediated carcinogenesis (Corcoran et al, 2008;Parathath et al, 2008). Gene expression analysis in keratinocytes indicates that EGF and hedgehog have synergistic effects on gene expression of MEK/ERK/JUN (Kasper et al, 2006;Schnidar et al, 2009). There is a hope that inhibition of Hh signaling and growth factor pathways will result in better treatment of cancer (Shaw and Prowse, 2008).…”

GLI1 facilitates the migration and invasion of pancreatic cancer cells through MUC5AC-mediated attenuation of E-cadherin

“…MUC5AC is a direct target of GLI1 GLI1 has been reported to control the expression of many downstream target genes, either directly or indirectly (Yoon et al, 2002;Eichberger et al, 2006;Kasper et al, 2006). To determine whether MUC5AC is a direct target of GLI1, we next generated two stable cell lines, PANC-1 GLI1ER and its control PANC-1 ER .…”

“…These clinical and experimental data highlight the importance of the downstream targets of GLI transcription factors in the development and cellular properties of PDA. Prior to this study, many attempts have been made to identify the transcriptional target genes of GLIs (Yoon et al, 2002;Eichberger et al, 2006;Kasper et al, 2006). However, whether GLIs regulate mucin expression remains unknown.…”