Identification of genes associated with head and neck carcinogenesis by cDNA microarray comparison between matched primary normal epithelial and squamous carcinoma cells

Biomarkers of human cutaneous squamous cell carcinoma from tissues and cell lines identified by DNA microarrays and qRT-PCR

Squamous cell carcinoma (SCC) is the second most common form of skin cancer in Caucasians. Here we report on the identification of biomarkers of human cutaneous SCC cell lines in vitro and tissue samples in vivo using DermArray and PharmArray DNA microarrays, consisting of ca. 7400 unique human cDNAs. Differentially expressed genes were identified in two facial skin SCC cell lines (SCC 12 and SCC 13) compared to normal keratinocytes, and three cutaneous SCC tissue samples compared to normal skin. Quantitative validations of up- and down-regulated biomarkers were performed by qRT-PCR on 23 biomarker genes for the cell lines and 20 biomarker genes for the tumor tissues. In addition, three oral SCC cell lines were also included in the qRT-PCR validations for comparison, and the biomarker profiles were highly similar between the cutaneous and the oral SCC cell lines for all 23 biomarkers examined. The expression profiles for a variety of non-cutaneous SCC types, such as head-and-neck, oral, and lung, have been previously published. This report is the first to describe biomarkers for cutaneous SCC in two contexts, in vitro and in vivo. Although there was minimal overlap between the two different contexts using DNA microarrays, five genes were found common to both the cell lines and tissues, namely fibronectin 1, annexin A5, glyceraldehyde 3-phosphate dehydrogenase, zinc-finger protein 254, and huntingtin-associated protein interacting protein. Some of our previously published biomarkers of normal keratinocytes were down-regulated in SCC, suggestive of the dedifferentiated status of the transformed cells. While recent reports have identified some of the same genes as SCC biomarkers, for instance in head-and-neck cancer, thereby validating our approach, we have identified some novel biomarkers for cutaneous disease. These biomarker lists may be useful in molecular diagnostics of non-melanoma skin cancer, and a subset of the biomarkers might serve as suitable targets for drug discovery efforts of therapies for SCC.

Regulation of tight junctions during the epithelium-mesenchyme transition: direct repression of the gene expression of claudins/occludin by Snail

Snail is a transcription repressor that plays a central role in the epithelium-mesenchyme transition (EMT), by which epithelial cells lose their polarity. Claudins and occludin are integral membrane proteins localized at tight junctions, which are responsible for establishing and maintaining epithelial cell polarity. We examined the relationship between Snail and the promoter activity of claudins and occludin. When Snail was overexpressed in cultured mouse epithelial cells, EMT was induced with concomitant repression of the expression of claudins and occludin not only at the protein but also at the mRNA level. We then isolated the promoters of genes encoding claudins and occludin, in which multiple E-boxes were identified. Transfection experiments with various promoter constructs as well as electrophoretic mobility assays revealed that Snail binds directly to the E-boxes of the promoters of claudin/occludin genes, resulting in complete repression of their promoter activity. Because the gene encoding E-cadherin was also reported to be repressed by Snail, we concluded that EMT was associated with the simultaneous repression of the genes encoding E-cadherin and claudins/occludin (i.e. the expression of adherens and tight junction adhesion molecules, respectively).

Profile of gene expression induced by the tumour promotor TPA in murine epithelial cells

Malignant transformation of mouse skin by chemical carcinogens and tumour promoters, such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), is a multistage process that leads to squamous cell carcinoma (SCC) formation. In an effort to identify tumour-associated genes, we studied the influence of short-term TPA-treatment on the gene expression profile of murine skin. A comprehensive microarray with some 5,000 murine gene specific cDNA fragments was established and hybridised with pooled RNA derived from control and TPA-treated dorsal skin samples. Of these genes, 54 were up- and 35 were down-regulated upon TPA application. Additionally, we performed suppression subtractive hybridisation (SSH) with respective RNA pools to generate and analyse a cDNA library enriched for TPA-inducible genes. Expression data of selected genes were confirmed by quantitative real-time PCR and Northern blot analysis. Comparison of microarray and SSH data revealed that 26% of up-regulated genes identified by expression profiling matched with those present in the SSH library. Besides numerous known genes, we identified a large set of unknown cDNAs that represent previously unrecognised TPA-regulated genes in murine skin with potential function in tumour promotion. Additionally, some TPA-induced genes, such as Sprr1A, Saa3, JunB, Il4ralpha, Gp38, RalGDS and Slpi exhibit high basal level in advanced stages of skin carcinogenesis, suggesting that at least a subgroup of the identified TPA-regulated genes may contribute to tumour progression and metastasis.

The interface between ErbB and non-ErbB receptors in tumor invasion: clinical implications and opportunities for target discovery

The molecular switches by which malignant cancer cells evolve from a confined to an invasive state are poorly understood, but seem to involve a progressive activation of a signaling network shared by several growth factor receptors and non-receptor molecules. Abnormal expression of ErbB tyrosine kinase receptors, commonly seen in cancer, is an early event in the invasive process, which makes these receptors exciting targets for drug discovery. The past few years have been full of promise for ErbB targeting in the context of receptor overexpression, but also fraught with disappointment as clinical efficacy has often been hampered by potential problems such as the heterogeneity of receptor expression within the same tumor, and the extensive cooperative signaling among ErbB and non-ErbB receptors. Cooperative signaling is a common characteristic of invasive cancer cells, and is believed to dictate the genetic program that controls invasion switches. Molecular studies on the combinatorial signaling involved in tumor invasion are becoming a fertile area for target discovery in cancer. This review discusses how cooperative signaling between ErbB and non-ErbB receptors regulates tumor invasion and hence provides multiple opportunities for drug discovery, and how current therapies and investigational drugs could pave the way to even more potent alternative combinatorial therapeutic approaches for invasive cancers.

Tight junction proteins

A fundamental function of epithelia and endothelia is to separate different compartments within the organism and to regulate the exchange of substances between them. The tight junction (TJ) constitutes the barrier both to the passage of ions and molecules through the paracellular pathway and to the movement of proteins and lipids between the apical and the basolateral domains of the plasma membrane. In recent years more than 40 different proteins have been discovered to be located at the TJs of epithelia, endothelia and myelinated cells. This unprecedented expansion of information has changed our view of TJs from merely a paracellular barrier to a complex structure involved in signaling cascades that control cell growth and differentiation. Both cortical and transmembrane proteins integrate TJs. Among the former are scaffolding proteins containing PDZ domains, tumor suppressors, transcription factors and proteins involved in vesicle transport. To date two components of the TJ filaments have been identified: occludin and claudin. The latter is a protein family with more than 20 members. Both occludin and claudins are integral proteins capable of interacting adhesively with complementary molecules on adjacent cells and of co-polymerizing laterally. These advancements in the knowledge of the molecular structure of TJ support previous physiological models that exhibited TJ as dynamic structures that present distinct permeability and morphological characteristics in different tissues and in response to changing natural, pathological or experimental conditions.

DNA microarray and cancer

Since the discovery of the first oncogene 26 years ago, a large body of research has convincingly demonstrated that the initiation and progression of cancers involve the accumulation of genetic aberrations in the cell. Many techniques have been developed to identify these genetic abnormalities. The recent completion of human genome sequencing and advances in DNA microarray technology allow rapid genetic analysis to take place on a genome-wide scale and have revolutionized the way cancers are studied. This ground-breaking approach of studying cancer promises to provide a better understanding of the underlying mechanism for tumorigenesis, more accurate diagnosis, more comprehensive prognosis, and more effective therapeutic interventions.

Post-analysis follow-up and validation of microarray experiments

Measurement of gene-expression profiles using microarray technology is becoming increasingly popular among the biomedical research community. Although there has been great progress in this field, investigators are still confronted with a difficult question after completing their experiments: how to validate the large data sets that are generated? This review summarizes current approaches to verifying global expression results, discusses the caveats that must be considered, and describes some methods that are being developed to address outstanding problems.

Regulation of E-cadherin/catenin complex patterns by epidermal growth factor receptor modulation in human lung cancer cells

We previously demonstrated that a ligand-blocking monoclonal antibody (mAb) against the epidermal growth factor-receptor (EGF-R), LA1, induced morphological conversion from epithelial-like to epithelial of the human lung cancer cell line, H322. This was accompanied by an up-regulation of epithelial cadherin (E-cadherin) expression (Clin. Cancer Res. 5 (1999) 681). In the present paper, we show that mAb LA1 induces the epithelial-like to epithelial conversion of the human lung cancer cell line, A549. In A549 and H322 cells, which express a detectable amount of EGF-R (ErbB-1), ErbB-2, ErbB-3, and ErbB-4 receptors, the LA1 mAb induces up-regulation of the E-cadherin/catenin complex (alpha-, beta-, and gamma-catenins). This is associated with re-localization of E-cadherin, alpha-catenin, (and to a lesser extent beta-catenin), but not gamma-catenin. Additionally, we report that mAb LA1 inhibits cell motility. In contrast, epidermal growth factor (EGF) or heparin-binding EGF-like growth factor (HB-EGF) induces the epithelial-like to fibroblastoid conversion of A549 and H322 cell lines, slightly reduces the expression of E-cadherin and beta-catenin, but not alpha- and gamma-catenins, and stimulates cell motility. These studies demonstrate that EGF-R modulation regulates the E-cadherin/catenin complex and cell motility in human lung epithelial carcinoma cells. Our results may have important therapeutic implications for the treatment of invasive human lung carcinomas via the restoration of the cadherin/catenin complex using inhibitors of EGF-R.