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FOXM1 is a downstream target of Gli1 in basal cell carcinomas
Muy-Teck Teh1, Soon-Tee Wong, Graham W Neill
1Centre for Cutaneous Research, Barts & The London School of Medicine and Dentistry, Queen Mary, University of London, London E1 2AT, United Kingdom. m.t.teh@qmul.ac.uk
Abstract:
Forkhead box (FOX) proteins have been shown to play important roles in regulating the expression of genes involved in cell growth, proliferation, differentiation, longevity, and transformation. The functional importance of this gene family in normal human skin physiology and disease processes is not well understood. Activation of Sonic Hedgehog (Shh) signaling plays a key role in the development of basal cell carcinomas (BCCs) of the skin in humans. Recent studies have established that some FOX genes are downstream targets of Shh signaling. We have investigated the role of FOX proteins in transducing Shh effects in human skin by using degenerate PCR to identify FOX genes differentially expressed in BCCs. All three known FOXM1 isoforms (a, b, and c) were detected in human skin and cultured keratinocytes, and the transcriptionally active FOXM1b isoform was found to be up-regulated in BCCs. Real-time quantitative RT-PCR showed that the increase in FOXM1 mRNA levels was specific for BCCs and not a reflection of increased cell proliferation in that no up-regulation was seen in squamous cell carcinomas or proliferating primary human keratinocyte cultures. Immunostaining studies showed intense nuclear and cytoplasmic staining throughout BCC tumor islands and not confined to the periphery regions of the tumor where proliferating Ki-67-immunopositive cells are predominantly localized. Expression of the Shh target glioma transcription factor-1 (Gli1) in primary keratinocytes and other cell lines caused a significant elevation of FOXM1 mRNA level and transcriptional activity, indicating that FOXM1 is a downstream target of Gli1. Our data provide the first evidence that activation of Shh signaling via Gli1 is an important determinant of FOXM1 expression in mammalian cells. Given the role of FOXM1 in cell proliferation, the up-regulation of FOXM1 in BCCs may be one of the mechanisms whereby Shh signaling exerts its mitogenic effect on basal keratinocytes, leading to the development of this common human cancer.
Insights
Forkhead box (FOX) proteins, including FOXM1, are upregulated in basal cell carcinomas (BCCs). Sonic Hedgehog (Shh) signaling activates FOXM1, suggesting a role in skin cancer development.
Area of Science:
- Molecular Biology
- Dermatology
- Oncology
Background:
- Forkhead box (FOX) proteins regulate critical cellular processes like growth and differentiation.
- The role of FOX proteins in human skin physiology and disease remains unclear.
- Sonic Hedgehog (Shh) signaling is implicated in basal cell carcinoma (BCC) development.
Purpose of the Study:
- To investigate the role of FOX proteins in transducing Shh signaling in human skin.
- To identify FOX genes differentially expressed in BCCs.
Main Methods:
- Degenerate PCR to identify differentially expressed FOX genes in BCCs.
- Real-time quantitative RT-PCR to quantify FOXM1 mRNA levels.
- Immunostaining to assess FOXM1 protein localization.
- Gene expression studies in keratinocytes and cell lines.
Main Results:
- All three FOXM1 isoforms were detected in human skin and keratinocytes.
- FOXM1b isoform was significantly upregulated in BCCs, specifically, not in other proliferating skin conditions.
- FOXM1 is a downstream target of Gli1, a key mediator of Shh signaling.
- FOXM1 expression is linked to Shh pathway activation via Gli1 in mammalian cells.
Conclusions:
- Activation of Shh signaling through Gli1 is a key regulator of FOXM1 expression in mammalian cells.
- Upregulated FOXM1 in BCCs may contribute to Shh-mediated mitogenic effects on basal keratinocytes.
- This study provides evidence for FOXM1's role in the pathogenesis of basal cell carcinoma.