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Carcinogenesis Advance Access originally published online on February 14, 2008
Carcinogenesis 2008 29(4):738-746; doi:10.1093/carcin/bgn037
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

GLI1 repression of ERK activity correlates with colony formation and impaired migration in human epidermal keratinocytes

Graham W. Neill1,*, Wesley J. Harrison1, Mohammed S. Ikram1, Tomos D.L. Williams1, Lucia S. Bianchi1, Sandeep K. Nadendla1, Judith L. Green1,3, Lucy Ghali1,4, Anna-Maria Frischauf2, Edel A. O'Toole1, Fritz Aberger2 and Michael P. Philpott1

1 Centre for Cutaneous Research, Institute of Cell and Molecular Science, Barts and The London School of Medicine and Dentistry, 4 Newark Street, London E1 2AT, UK
2 Department of Molecular Biology, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria
3 Present address: Division of Parasitology, MRC National Institute for Medical Research, London NW7 1AA UK
4 Present address: Department of Biomedical Sciences, School of Health and Social Sciences, Middlesex University, Enfield EN3 4SA UK

* To whom correspondence should be addressed. Tel: +44 207 882 2343; Fax: +44 207 882 7172; Email: g.w.neill{at}qmul.ac.uk

Basal cell carcinoma (BCC) of the skin is a highly compact, non-metastatic epithelial tumour type that may arise from the aberrant propagation of epidermal or progenitor stem cell (SC) populations. Increased expression of GLI1 is a common feature of BCC and is linked to the induction of epidermal SC markers in immortalized N/Tert-1 keratinocytes. Here, we demonstrate that GLI1 over-expression is linked to additional SC characteristics in N/Tert-1 cells including reduced epidermal growth factor receptor (EGFR) expression and compact colony formation that is associated with repressed extracellular signal-regulated kinase (ERK) activity. Colony formation and repressed ERK activity remain evident when EGFR is increased exogenously to the basal levels in GLI1 cells revealing that ERK is additionally inhibited downstream of the receptor. Exposure to epidermal growth factor (EGF) to increase ERK activity and promote migration negates GLI1 colony formation with cells displaying an elongated, fibroblast-like morphology. However, as determined by Snail messenger RNA and E-cadherin protein expression this is not associated with epithelial–mesenchymal transition (EMT), and GLI1 actually represses induction of the EMT marker vimentin in EGF-stimulated cells. Instead, live cell imaging revealed that the elongated morphology of EGF/GLI1 keratinocytes stems from their being ‘stretched’ due to migrating cells displaying inefficient cell–cell detachment and impaired tail retraction. Taken together, these data suggest that GLI1 opposes EGFR signalling to maintain the epithelial phenotype. Finally, ERK activity was predominantly negative in 13/14 BCCs (superficial/nodular), indicating that GLI1 does not routinely co-operate with ERK to induce the formation of this common skin tumour.

Abbreviations: BCC, basal cell carcinoma; EGFR, epidermal growth factor receptor; EMT, epithelial–mesenchymal transition; ERK, extracellular signal-regulated kinase; HEK, human epidermal keratinocyte; JNK, c-jun N-terminal kinase; mRNA, messenger RNA; PBS, phosphate-buffered saline; PDGFR{alpha}, platelet-derived growth factor receptor alpha; qPCR, quantitative polymerase chain reaction; RT, room temperature; SC, stem cell; SHH, Sonic hedgehog

Received August 24, 2007; revised December 19, 2007; accepted January 26, 2008.


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