Alterations in keratins and associated proteins during 4- Nitroquinoline-1-oxide induced rat oral carcinogenesis

Role of Hemidesmosomes in Oral Carcinogenesis: A Systematic Review

BACKGROUND

Oral cancers have limited diagnostic tools to aid clinical management. Current evidence indicates that alterations in hemidesmosomes, the adhesion complexes primarily involved in epithelial attachment to the basement membrane, are correlated to cancer phenotype for multiple cancers. This systematic review aimed to assess the experimental evidence for hemidesmosomal alterations, specifically in relation to oral potentially malignant disorders and oral squamous cell carcinomas.

METHODS

We conducted a systemic review to summarise the available literature on hemidesmosomal components and their role in oral pre-cancer and cancer. Relevant studies were retrieved from a comprehensive search of Scopus, Ovid MEDLINE, Ovid Embase and Web of Science.

RESULTS

26 articles met the inclusion criteria, of which 19 were in vitro studies, 4 in vivo studies, 1 in vitro and in vivo study, and 2 in vitro and cohort studies. Among them, 15 studies discussed individual alpha-6 and/or beta-4 subunits, 12 studies discussed the alpha-6 beta-4 heterodimers, 6 studies discussed the entire hemidesmosome complex, 5 studies discussed bullous pemphigoid-180, 3 studies discussed plectin, 3 studies discussed bullous pemphigoid antigen-1 and 1 study discussed tetraspanin.

CONCLUSION

Heterogeneity in cell type, experimental models, and methods were observed. Alterations in hemidesmosomal components were shown to contribute to oral pre-cancer and cancer. We conclude that there is sufficient evidence for hemidesmosomes and their components to be potential biomarkers for evaluating oral carcinogenesis.

Multifaceted role of keratins in epithelial cell differentiation and transformation

Keratins, the epithelial-predominant members of the intermediate filament superfamily, are expressed in a pairwise, tissuespecific and differentiation-dependent manner. There are 28 type I and 26 type II keratins, which share a common structure comprising a central coiled coil α-helical rod domain flanked by two nonhelical head and tail domains. These domains harbor sites for major posttranslational modifications like phosphorylation and glycosylation, which govern keratin function and dynamics. Apart from providing structural support, keratins regulate various signaling machinery involved in cell growth, motility, apoptosis etc. However, tissue-specific functions of keratins in relation to cell proliferation and differentiation are still emerging. Altered keratin expression pattern during and after malignant transformation is reported to modulate different signaling pathways involved in tumor progression in a context-dependent fashion. The current review focuses on the literature related to the role of keratins in the regulation of cell proliferation, differentiation and transformation in different types of epithelia.

The dynamics of gene expression changes in a mouse model of oral tumorigenesis may help refine prevention and treatment strategies in patients with oral cancer

A better understanding of the dynamics of molecular changes occurring during the early stages of oral tumorigenesis may help refine prevention and treatment strategies. We generated genome-wide expression profiles of microdissected normal mucosa, hyperplasia, dysplasia and tumors derived from the 4-NQO mouse model of oral tumorigenesis. Genes differentially expressed between tumor and normal mucosa defined the “tumor gene set” (TGS), including 4 non-overlapping gene subsets that characterize the dynamics of gene expression changes through different stages of disease progression. The majority of gene expression changes occurred early or progressively. The relevance of these mouse gene sets to human disease was tested in multiple datasets including the TCGA and the Genomics of Drug Sensitivity in Cancer project. The TGS was able to discriminate oral squamous cell carcinoma (OSCC) from normal oral mucosa in 3 independent datasets. The OSCC samples enriched in the mouse TGS displayed high frequency of CASP8 mutations, 11q13.3 amplifications and low frequency of PIK3CA mutations. Early changes observed in the 4-NQO model were associated with a trend toward a shorter oral cancer-free survival in patients with oral preneoplasia that was not seen in multivariate analysis. Progressive changes observed in the 4-NQO model were associated with an increased sensitivity to 4 different MEK inhibitors in a panel of 51 squamous cell carcinoma cell lines of the aerodigestive tract. In conclusion, the dynamics of molecular changes in the 4-NQO model reveal that MEK inhibition may be relevant to prevention and treatment of a specific molecularly-defined subgroup of OSCC.

Identification of reliable reference genes for quantitative gene expression studies in oral squamous cell carcinomas compared to adjacent normal tissues in the F344 rat model

Oral squamous cell carcinomas (OSCCs) induced in F344 rats by 4-nitroquinoline-1-oxide (4-NQO) demonstrate considerable phenotypic similarity to human oral cancers and the model has been widely used for carcinogenesis and chemoprevention studies. Molecular characterization of this model needs reliable reference genes (RGs) to avoid false- positive and -negative results for proper interpretation of gene expression data between tumor and adjacent normal tissues. Microarray analysis of 11 pairs of OSCC and site-matched phenotypically normal oral tissues from 4-NQO-treated rats identified 10 stably expressed genes in OSCC compared to adjacent normal tissues (p>0.5, CV<15%) that could serve as potential RGs in this model. The commonly used 27 RGs in the rat were also analyzed based on microarray data and most of them were found unsuitable for RGs in this model. Traditional RGs such as ACTB and GAPDH were significantly altered in OSCC compared to adjacent normal tissues (p<0.01, n=11); however, the Hsp90ab1 was ranked as the best RG candidate and the combination of Hsp90ab1 and HPRT1 was identified by NormFinder to be a superior reference for gene normalization among the commonly used RGs. This result was also validated by RT-PCR based on the selected top RG candidate pool. These data suggest that there are no common RGs suitable for different models and RG(s) should be identified before gene expression analysis. We successfully identified Hsp90ab1 as a stable RG in 4-NQO-induced OSCC compared to adjacent normal tissues in F344 rats. The combination of two stably expressed genes may be a better option for gene normalization in tissue samples.

Overexpression of lipocalins and pro-inflammatory chemokines and altered methylation of PTGS2 and APC2 in oral squamous cell carcinomas induced in rats by 4-nitroquinoline-1-oxide

Oral squamous cell carcinomas (OSCC) induced in F344 rats by 4-nitroquinoline-1-oxide (4-NQO) demonstrate considerable phenotypic similarity to human oral cancers. Gene expression studies (microarray and PCR) were coupled with methylation analysis of selected genes to identify molecular markers of carcinogenesis in this model and potential biochemical and molecular targets for oral cancer chemoprevention. Microarray analysis of 11 pairs of OSCC and site-matched phenotypically normal oral tissues from 4-NQO-treated rats identified more than 3500 differentially expressed genes; 1735 genes were up-regulated in rat OSCC versus non-malignant tissues, while 1803 genes were down-regulated. In addition to several genes involved in normal digestion, genes demonstrating the largest fold increases in expression in 4-NQO-induced OSCC include three lipocalins (VEGP1, VEGP2, LCN2) and three chemokines (CCL, CXCL2, CXCL3); both classes are potentially druggable targets for oral cancer chemoprevention and/or therapy. Down-regulated genes in 4-NQO-induced OSCC include numerous keratins and keratin-associated proteins, suggesting that alterations in keratin expression profiles may provide a useful biomarker of oral cancer in F344 rats treated with 4-NQO. Confirming and extending our previous results, PTGS2 (cyclooxygenase-2) and several cyclooxygenase-related genes were significantly up-regulated in 4-NQO-induced oral cancers; up-regulation of PTGS2 was associated with promoter hypomethylation. Rat OSCC also demonstrated increased methylation of the first exon of APC2; the increased methylation was correlated with down-regulation of this tumor suppressor gene. Overexpression of pro-inflammatory chemokines, hypomethylation of PTGS2, and hypermethylation of APC2 may be causally linked to the etiology of oral cancer in this model.