A positive FGFR3/FOXN1 feedback loop underlies benign skin keratosis versus squamous cell carcinoma formation in humans
Anna Mandinova, … , Janice L. Brissette, G. Paolo Dotto
Anna Mandinova, … , Janice L. Brissette, G. Paolo Dotto
Published September 1, 2009
Citation Information: J Clin Invest. 2009;119(10):3127-3137. https://doi.org/10.1172/JCI38543.
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Research Article Dermatology

A positive FGFR3/FOXN1 feedback loop underlies benign skin keratosis versus squamous cell carcinoma formation in humans

Abstract

Seborrheic keratoses (SKs) are common, benign epithelial tumors of the skin that do not, or very rarely, progress into malignancy, for reasons that are not understood. We investigated this by gene expression profiling of human SKs and cutaneous squamous cell carcinomas (SCCs) and found that several genes previously connected with keratinocyte tumor development were similarly modulated in SKs and SCCs, whereas the expression of others differed by only a few fold. In contrast, the tyrosine kinase receptor FGF receptor–3 (FGFR3) and the transcription factor forkhead box N1 (FOXN1) were highly expressed in SKs, and close to undetectable in SCCs. We also showed that increased FGFR3 activity was sufficient to induce FOXN1 expression, counteract the inhibitory effect of EGFR signaling on FOXN1 expression and differentiation, and induce differentiation in a FOXN1-dependent manner. Knockdown of FOXN1 expression in primary human keratinocytes cooperated with oncogenic RAS in the induction of SCC-like tumors, whereas increased FOXN1 expression triggered the SCC cells to shift to a benign SK-like tumor phenotype, which included increased FGFR3 expression. Thus, we have uncovered a positive regulatory loop between FGFR3 and FOXN1 that underlies a benign versus malignant skin tumor phenotype.

Authors

Anna Mandinova, Vihren Kolev, Victor Neel, Bing Hu, Wesley Stonely, Jocelyn Lieb, Xunwei Wu, Claudia Colli, Rong Han, Mike Pazin, Paola Ostano, Reinhard Dummer, Janice L. Brissette, G. Paolo Dotto

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Figure 5

FGFR3 activation induces keratinocyte differentiation through a FOXN1-dependent mechanism.

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FGFR3 activation induces keratinocyte differentiation through a FOXN1-de...
(A and B) Human keratinocytes were treated with 1 ng/ml EGF or 5 ng/ml FGF9 separately or in combination for 24 hours followed by real-time RT-PCR analysis of keratin1 (A) and involucrin (B). (C) Human keratinocytes treated as in A and B were analyzed for involucrin expression by immunoblotting with γ-tubulin as equal loading control. (D) Human keratinocytes were transfected with anti-FOXN1 siRNAs or scrambled siRNA control followed 48 hours later by real-time RT-PCR analysis to verify efficacy of gene knockdown. (E) Keratinocytes transfected with anti-FOXN1 siRNAs or scrambled siRNA control as in D were left untreated or treated with 5 ng/ml FGF9 for the last 24 hours of the experiment. Expression levels of keratin1 and involucrin were determined by real-time RT-PCR. (F) Primary human keratinocytes transfected with FOXN1 siRNA were left untreated or treated with FGF9 as in E, followed by immunoblot analysis of involucrin expression with γ-tubulin as equal loading control. Results were quantified by densitometric scanning of the immunoblots and normalization for γ-tubulin. All error bars denote SEM.