Abstract
BackgroundCancer associated with smoking and drinking remains a serious health problem worldwide. The survival of patients is very poor due to the lack of effective early biomarkers. FOXM1 overexpression is linked to the majority of human cancers but its mechanism remains unclear in head and neck squamous cell carcinoma (HNSCC).Methodology/Principal FindingsFOXM1 mRNA and protein expressions were investigated in four independent cohorts (total 75 patients) consisting of normal, premalignant and HNSCC tissues and cells using quantitative PCR (qPCR), expression microarray, immunohistochemistry and immunocytochemistry. Effect of putative oral carcinogens on FOXM1 transcriptional activity was dose-dependently assayed and confirmed using a FOXM1-specific luciferase reporter system, qPCR, immunoblotting and short-hairpin RNA interference. Genome-wide single nucleotide polymorphism (SNP) array was used to ‘trace’ the genomic instability signature pattern in 8 clonal lines of FOXM1-induced malignant human oral keratinocytes. Furthermore, acute FOXM1 upregulation in primary oral keratinocytes directly induced genomic instability. We have shown for the first time that overexpression of FOXM1 precedes HNSCC malignancy. Screening putative carcinogens in human oral keratinocytes surprisingly showed that nicotine, which is not perceived to be a human carcinogen, directly induced FOXM1 mRNA, protein stabilisation and transcriptional activity at concentrations relevant to tobacco chewers. Importantly, nicotine also augmented FOXM1-induced transformation of human oral keratinocytes. A centrosomal protein CEP55 and a DNA helicase/putative stem cell marker HELLS, both located within a consensus loci (10q23), were found to be novel targets of FOXM1 and their expression correlated tightly with HNSCC progression.Conclusions/SignificanceThis study cautions the potential co-carcinogenic effect of nicotine in tobacco replacement therapies. We hypothesise that aberrant upregulation of FOXM1 may be inducing genomic instability through a program of malignant transformation involving the activation of CEP55 and HELLS which may facilitate aberrant mitosis and epigenetic modifications. Our finding that FOXM1 is upregulated early during oral cancer progression renders FOXM1 an attractive diagnostic biomarker for early cancer detection and its candidate mechanistic targets, CEP55 and HELLS, as indicators of malignant conversion and progression.
Highlights
The forkhead box (FOX) protein family of transcription factors exhibit a myriad of biological functions such as regulation of cell cycle, proliferation, apoptosis, differentiation and longevity during embryonic development and adult tissue homeostasis [reviewed in 1]
We originally established a link between FOXM1 and tumourigenesis when we demonstrated that FOXM1 was a downstream target of Gli1 in basal cell carcinoma (BCC) and showed that of the three known alternatively spliced isoforms (FOXM1A, B and C), FOXM1B isoform was overexpressed in BCCs [5]
Our bioinformatics analysis based on a panel of microarray data [11] showed that FOXM1 mRNA expression was significantly upregulated in both premalignant dysplastic lesions and head and neck squamous cell carcinoma (HNSCC) compared to normal oral mucosa (Fig. 1B)
Summary
The forkhead box (FOX) protein family of transcription factors exhibit a myriad of biological functions such as regulation of cell cycle, proliferation, apoptosis, differentiation and longevity during embryonic development and adult tissue homeostasis [reviewed in 1]. The FOXM1 transcription factor (previously known as: HFH11, INS-1, WIN, MPP2/MPHOSPH2 or Trident/FKHL16) has been shown to play important roles in cell cycle progression and mitosis [reviewed in 2]. We originally established a link between FOXM1 and tumourigenesis when we demonstrated that FOXM1 was a downstream target of Gli in basal cell carcinoma (BCC) and showed that of the three known alternatively spliced isoforms (FOXM1A, B and C), FOXM1B isoform was overexpressed in BCCs [5]. Both transcriptional activators FOXM1B and FOXM1C are upregulated in the majority of solid human cancers [reviewed in 2,6]. FOXM1 overexpression is linked to the majority of human cancers but its mechanism remains unclear in head and neck squamous cell carcinoma (HNSCC)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
