Gene mutations and increased levels of p53 protein in human squamous cell carcinomas and their cell lines

Establishment and characterization of a novel hypopharyngeal squamous cell carcinoma cell line CZH1 with genetic abnormalities

Hypopharyngeal squamous cell carcinoma (HPSCC) has the worst prognosis among head and neck squamous cell carcinomas. The lack of available tumor cell lines poses a significant obstacle to the development of efficient treatments for HPSCC. In this study, we successfully established a novel cell line, named CZH1, from the postcricoid region of a Chinese male patient with a T3N0M0 HPSCC. Short tandem repeat analysis confirmed the uniqueness of CZH1. The cell line was characterized by its phenotypes, biomarkers, and genetics. Importantly, CZH1 cells retained the typical features of epithelial malignancy, similar to the primary tumor tissue. Furthermore, CZH1 demonstrated a greater capacity for invasion and increased susceptibility to irradiation in comparison to FaDu, which is the most commonly used HPSCC cell line. Whole-exome sequencing analysis revealed that CZH1 cells had typical genomic features of HNSCC, including mutations of TP53 and amplifications of multiple transcripts. Therefore, our newly developed CZH1 cell line could serve as an efficient tool for the in vitro investigation of the etiology, pathogenesis, and preclinical treatment of HPSCC.

Loss of p53 activates thyroid hormone via type 2 deiodinase and enhances DNA damage

The Thyroid Hormone (TH) activating enzyme, type 2 Deiodinase (D2), is functionally required to elevate the TH concentration during cancer progression to advanced stages. However, the mechanisms regulating D2 expression in cancer still remain poorly understood. Here, we show that the cell stress sensor and tumor suppressor p53 silences D2 expression, thereby lowering the intracellular THs availability. Conversely, even partial loss of p53 elevates D2/TH resulting in stimulation and increased fitness of tumor cells by boosting a significant transcriptional program leading to modulation of genes involved in DNA damage and repair and redox signaling. In vivo genetic deletion of D2 significantly reduces cancer progression and suggests that targeting THs may represent a general tool reducing invasiveness in p53-mutated neoplasms.

ACTL6A suppresses p21Cip1 expression to enhance the epidermal squamous cell carcinoma phenotype

Epidermal squamous cell carcinoma (SCC) is a common and highly invasive form of cancer. SCC arises due to ultraviolet light exposure and is associated with increased expression of pro-cancer genes and reduced expression of cancer suppressors. Actin-Like Protein 6A (ACTL6A, BAF53a) is an important protein subunit of the SWI/SNF epigenetic chromatin regulatory complex. ACTL6A is elevated in cancer cells and has been implicated as a driver of cancer cell proliferation and tumor growth. In the present study, we show that ACTL6A drives SCC cell proliferation, spheroid formation, invasion and migration, and that these activities are markedly reduced by ACTL6A knockdown. We further show that ACTL6A expression is associated with reduced levels of the p21^Cip1 cyclin-dependent kinase inhibitor and tumor suppressor protein. Molecular studies show that ACTL6A interacts with p53 DNA response elements in the p21^Cip1 gene promoter to suppress p21^Cip1 promoter activity and mRNA and protein level. Additional studies show that an increase in p21^Cip1 expression in ACTL6A knockdown cells is required for suppression of the SCC cell phenotype, suggesting that p21^Cip1 is a mediator of ACTL6A action. We further show that this regulation is p53 independent. These findings suggest that ACTL6A suppresses p21^Cip1 promoter activity to reduce p21^Cip1 protein as a mechanism to maintain the aggressive epidermal SCC phenotype.

Stage-dependent therapeutic efficacy in PI3K/mTOR-driven squamous cell carcinoma of the skin

Cutaneous squamous cell carcinoma (SCC) is a recurrent cancer that is prevalent in predisposed subjects such as immunosuppressed patients and patients being treated for other malignancies. Model systems to trial therapies at different stages of SCC development are lacking, therefore precluding efficient therapeutic interventions. Here, we have disrupted the expression of the tumor suppressor GRHL3 to induce loss of PTEN and activation of the PI3K/mTOR signaling pathway in mice and human skin, promoting aggressive SCC development. We then examined the potential for targeting PI3K/mTOR and an oncogenic driver miR-21, alone and in combination, for the prevention and treatment of SCC during the initiation, promotion/progression and establishment stages. Treatment with PI3K/mTOR inhibitors completely prevented tumor initiation, and these inhibitors significantly delayed the course of papilloma progression to malignancy. However, established SCC did not undergo any growth regression, indicating that this therapy is ineffective in established cancers. Mechanistically, the resistant SCCs displayed increased miR-21 expression in mice and humans where antagonists of miR-21 rescued expression levels of GRHL3/PTEN, but the combination of miR-21 antagonism with PI3K/mTOR inhibition resulted in acquired SCC resistance in part via c-MYC and OCT-4 upregulation. In conclusion, our data provide molecular evidence for the efficacy of targeting oncogenic drivers of SCC during the initiation and promotion stages and indicate that combination therapy may induce an aggressive phenotype when applied in the establishment stage.

The rare nonsense mutation in p53 triggers alternative splicing to produce a protein capable of inducing apoptosis

P53 protein is more frequently mutated in human tumours compared with the other proteins. While the majority of the p53 mutations, especially within its DNA-binding domain, lead to the loss of the wild-type function, there are accumulating data demonstrating that the p53 mutants gain tumour promoting activities; the latter triggers a revitalised interest in functional analysis of the p53 mutants. A systematic screening for p53 mutations in surgical materials from patients with glioma revealed a 378C>G mutation that creates a stop codon at the position of amino acid residue 126. The mutation eliminates the recognition site for the restriction endonuclease Sca I that allowed us to carry out RFLP analysis of DNA extracted from the clinical samples and suggests that this mutation is more frequent than is documented in the p53 databases. Both the ECV-304 and EJ cell lines, that probably originate from the bladder carcinoma T24 cell line, were confirmed to contain the homozygous 378C>G mutation but were shown to produce the p53 protein of expected full-length size detected by Western blotting. We provide evidence that the 378C>G mutation generates an alternative 3’ splice site (ss) which is more often used instead of the authentic upstream 3’ ss, driving the production of mRNA encoding the protein with the single amino acid deletion (p53ΔY126). Using endogenous expression, we demonstrated that the p53ΔY126 protein is nearly as active as the wild type protein in inducing the p21/Waf1 expression and apoptosis.

Survival of Head and Neck Cancer Cells Relies upon LZK Kinase-Mediated Stabilization of Mutant p53

Head and neck squamous cell carcinoma (HNSCC) includes epithelial cancers of the oral and nasal cavity, larynx, and pharynx and accounts for ∼350,000 deaths per year worldwide. Smoking-related HNSCC is associated with few targetable mutations but is defined by frequent copy-number alteration, the most common of which is gain at 3q. Critical 3q target genes have not been conclusively determined for HNSCC. Here, we present data indicating that MAP3K13 (encoding LZK) is an amplified driver gene in HNSCC. Copy-number gain at 3q resulted in increased MAP3K13 mRNA in HNSCC tumor samples and cell lines. Silencing LZK reduced cell viability and proliferation of HNSCC cells with 3q gain but not control cell lines. Inducible silencing of LZK caused near-complete loss of colony-forming ability in cells harboring 3q gain. These results were validated in vivo by evidence that LZK silencing was sufficient to reduce tumor growth in a xenograft model of HNSCC. Our results establish LZK as critical for maintaining expression of mutant stabilized p53. Cancer Res; 77(18); 4961-72. ©2017 AACR.

Inefficient differentiation response to cell cycle stress leads to genomic instability and malignant progression of squamous carcinoma cells

Squamous cell carcinoma (SCC) or epidermoid cancer is a frequent and aggressive malignancy. However in apparent paradox it retains the squamous differentiation phenotype except for very dysplastic lesions. We have shown that cell cycle stress in normal epidermal keratinocytes triggers a squamous differentiation response involving irreversible mitosis block and polyploidisation. Here we show that cutaneous SCC cells conserve a partial squamous DNA damage-induced differentiation response that allows them to overcome the cell division block. The capacity to divide in spite of drug-induced mitotic stress and DNA damage made well-differentiated SCC cells more genomically instable and more malignant in vivo. Consistently, in a series of human biopsies, non-metastatic SCCs displayed a higher degree of chromosomal alterations and higher expression of the S phase regulator Cyclin E and the DNA damage signal γH2AX than the less aggressive, non-squamous, basal cell carcinomas. However, metastatic SCCs lost the γH2AX signal and Cyclin E, or accumulated cytoplasmic Cyclin E. Conversely, inhibition of endogenous Cyclin E in well-differentiated SCC cells interfered with the squamous phenotype. The results suggest a dual role of cell cycle stress-induced differentiation in squamous cancer: the resulting mitotic blocks would impose, when irreversible, a proliferative barrier, when reversible, a source of genomic instability, thus contributing to malignancy.

Deficient Nucleotide Excision Repair in Squamous Cell Carcinoma Cells

Squamous cell carcinomas (SCCs) are associated with ultraviolet radiation and multiple genetic changes, but the mechanisms leading to genetic instability are unclear. SCC cell lines were compared to normal keratinocytes for sensitivity to ultraviolet radiation, DNA repair kinetics and DNA repair protein expression. Relative to normal keratinocytes, four SCC cell lines were all variably sensitive to ultraviolet radiation and, except for the SCC25 cell line, were deficient in global repair of cyclobutane pyrimidine dimers, although not 6-4 photoproducts. Impaired DNA repair of cyclobutane pyrimidine dimers was associated with reduced mRNA expression from XPC but not DDB2 genes which each encode key DNA damage recognition proteins. However, levels of XPC or DDB2 proteins or both were variably reduced in repair-deficient SCC cell lines. p53 levels did not correlate with DNA repair activity or with XPC and DDB2 levels, but p63 levels were deficient in cell lines with reduced global repair. Repair-proficient SCC25 cells depleted of p63 lost XPC expression, early global DNA repair activity and UV resistance. These results demonstrate that some SCC cell lines are deficient in global nucleotide excision repair and support a role for p63 as a regulator of nucleotide excision repair in SCCs.

The homeoprotein DLX3 and tumor suppressor p53 co-regulate cell cycle progression and squamous tumor growth

Epidermal homeostasis depends on the coordinated control of keratinocyte cell cycle. Differentiation and the alteration of this balance can result in neoplastic development. Here we report on a novel DLX3-dependent network that constrains epidermal hyperplasia and squamous tumorigenesis. By integrating genetic and transcriptomic approaches, we demonstrate that DLX3 operates through a p53-regulated network. DLX3 and p53 physically interact on the p21 promoter to enhance p21 expression. Elevating DLX3 in keratinocytes produces a G1-S blockade associated with p53 signature transcriptional profiles. In contrast, DLX3 loss promotes a mitogenic phenotype associated with constitutive activation of ERK. DLX3 expression is lost in human skin cancers and is extinguished during progression of experimentally induced mouse squamous cell carcinoma (SCC). Reinstatement of DLX3 function is sufficient to attenuate the migration of SCC cells, leading to decreased wound closure. Our data establish the DLX3-p53 interplay as a major regulatory axis in epidermal differentiation and suggest that DLX3 is a modulator of skin carcinogenesis.

The role of HOXB9 and miR-196a in head and neck squamous cell carcinoma

Background

Previous studies have demonstrated that a number of HOX genes, a family of transcription factors with key roles in early development, are up-regulated in head and neck squamous cell carcinoma (HNSCC) and other cancers. The loci of several Homeobox (HOX) genes also contain microRNAs (miRs), including miR-196a.

Methods

Global miR expression and expression of all 39 HOX genes in normal oral keratinocytes (NOKs), oral pre-malignant (OPM) and HNSCC cells was assessed by expression microarray and qPCR and in tissues by immunohistochemistry (IHC) and qPCR of laser microdissected (LCM) tissues. Expression of miR196a and HOXB9 was reduced using anti-miR-196a and siRNA, respectively. Expression microarray profiles of anti-miR196a and pre-miR196a transfected cells were compared to parental cells in order to identify novel targets of miR-196a. Putative miR196a targets were validated by qPCR and were confirmed as binding to the 3’UTR of miR196a by a dual luciferase reporter assay combined with mutational analysis of the miR-196a binding site.

Results

miR-196a and HOXB9 are highly expressed in HNSCC compared to NOKs, a pattern also seen in HNSCC tissues by HOXB9 IHC and qPCR of miR-196a in LCM tissue. Knock-down of miR-196a expression decreased HNSCC cell migration, invasion and adhesion to fibronectin, but had no effect on proliferation. Furthermore, knock-down of HOXB9 expression decreased migration, invasion and proliferation but did not alter adhesion. We identified a novel primary mRNA transcript containing HOXB9 and miR196a-1 as predicted from in-silico analysis. Expression array analysis identified a number of miR196a targets, including MAMDC2 and HOXC8. We confirmed that MAMDC2 is a novel miR-196a target using a dual luciferase reporter assay with the effect abolished on mutation of the binding site.

Conclusions

These results show that miR-196a and HOXB9 are overexpressed, perhaps co-ordinately, as HNSCC develops and exert a pro-tumourigenic phenotype in HNSCC and OPM cells.

Phenethyl isothiocyanate induces DNA damage-associated G2/M arrest and subsequent apoptosis in oral cancer cells with varying p53 mutations

Phenethyl isothiocyanate (PEITC) is a naturally occurring cruciferous vegetable-derived compound that inhibits cell growth and induces apoptosis in oral cancer cells. However, the exact mechanism of PEITC action has not been fully elucidated. This study investigated the molecular mechanism and anticancer potential of PEITC in oral squamous cell carcinoma (OSCC) cells with various p53 statuses. PEITC inhibited the growth of OC2, SCC4, and SCC25 cells (functional p53 mutants) in a dose-dependent manner with low toxicity to normal cells. Treatment with PEITC induced reactive oxygen species production, nitric oxide generation, and GSH depletion and triggered DNA damage response as evidenced by flow cytometry, 8-OHdG formation, and comet assay. Furthermore, the subsequent activation of ATM, Chk2, and p53 as well as the increased expression of downstream proteins p21 and Bax resulted in a G2/M phase arrest by inhibiting Cdc25C, Cdc2, and cyclin B1. The PEITC-induced apoptotic cell death, following a diminished mitochondrial transmembrane potential, reduced the expression of Bcl-2 and Mcl-1, released mitochondrial cytochrome c, and activated caspase 3 and PARP cleavage. The p53 inhibitor pifithrin-α and the antioxidants N-acetylcysteine and glutathione (GSH) protected the cells from PEITC-mediated apoptosis. However, mito-TEMPO, catalase, apocynin, and L-NAME did not prevent PEITC-induced cell death, suggesting that PEITC induced G2/M phase arrest and apoptosis in oral cancer cells via a GSH redox stress and oxidative DNA damage-induced ATM-Chk2-p53-related pathway. These results provide new insights into the critical roles of both GSH redox stress and p53 in the regulation of PEITC-induced G2/M cell cycle arrest and apoptosis in OSCCs.

Identification and characterization of Dicer1e, a Dicer1 protein variant, in oral cancer cells

Background

The human dicer1 gene has been predicted to produce several mRNA variants that encode truncated Dicer1 proteins of varying lengths. One of these Dicer1 variants, Dicer1e, was recently found to be differentially expressed in breast cancer cells. Because the expression and function of the Dicer1e protein variant has not been well characterized and the underlying molecular mechanisms for the development of oral squamous cell carcinomas (OSCCs) are poorly understood, the present study sought to characterize the biological role of Dicer1e and determine its relationship, if any, to OSCC pathogenesis.

Methods

Western blot analyses were used to examine Dicer1e expression levels in a panel of oral cancer cells/tissues and during epithelial-mesenchymal transition (EMT), followed by 5′/3′-RACE analyses to obtain the full-length Dicer1e transcript. Biochemical fractionation and indirect immunofluorescent studies were performed to determine the cellular localization of Dicer1e and the effects of Dicer1e silencing on cancer cell proliferation, clonogenicity, and drug sensitivity were also assessed.

Results

Dicer1e protein levels were found to be overexpressed in OSCC cell lines of epithelial phenotype and in OSCC tissues with its levels downregulated during EMT. Moreover, the Dicer1e protein was observed to predominantly localize in the nucleus. 5′/3′-RACE analyses confirmed the presence of the Dicer1e transcript and silencing of Dicer1e impaired both cancer cell proliferation and clonogenicity by inducing either apoptosis and/or G2/M cell cycle arrest. Lastly, Dicer1e knockdown enhanced the chemosensitivity of oral cancer cells to cisplatin.

Conclusion

The expression levels of Dicer1e influence the pathogenesis of oral cancer cells and alter their response to chemosensitivity, thus supporting the importance of Dicer1e as a therapeutic target for OSCCs.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-190) contains supplementary material, which is available to authorized users.

Cold atmospheric plasma treatment selectively targets head and neck squamous cell carcinoma cells

The treatment of locoregional recurrence (LRR) of head and neck squamous cell carcinoma (HNSCC) often requires a combination of surgery, radiation therapy and/or chemotherapy. Survival outcomes are poor and the treatment outcomes are morbid. Cold atmospheric plasma (CAP) is an ionized gas produced at room temperature under laboratory conditions. We have previously demonstrated that treatment with a CAP jet device selectively targets cancer cells using in vitro melanoma and in vivo bladder cancer models. In the present study, we wished to examine CAP selectivity in HNSCC in vitro models, and to explore its potential for use as a minimally invasive surgical approach that allows for specific cancer cell or tumor tissue ablation without affecting the surrounding healthy cells and tissues. Four HNSCC cell lines (JHU-022, JHU-028, JHU-029, SCC25) and 2 normal oral cavity epithelial cell lines (OKF6 and NOKsi) were subjected to cold plasma treatment for durations of 10, 30 and 45 sec, and a helium flow of 20 l/min-1 for 10 sec was used as a positive treatment control. We showed that cold plasma selectively diminished HNSCC cell viability in a dose-response manner, as evidenced by MTT assays; the viability of the OKF6 cells was not affected by the cold plasma. The results of colony formation assays also revealed a cell-specific response to cold plasma application. Western blot analysis did not provide evidence that the cleavage of PARP occurred following cold plasma treatment. In conclusion, our results suggest that cold plasma application selectively impairs HNSCC cell lines through non-apoptotic mechanisms, while having a minimal effect on normal oral cavity epithelial cell lines.

Evidences suggesting involvement of viruses in oral squamous cell carcinoma

Oral cancer is one of the most common cancers and it constitutes a major health problem particularly in developing countries. Oral squamous cell carcinoma (OSCC) represents the most frequent of all oral neoplasms. Several risk factors have been well characterized to be associated with OSCC with substantial evidences. The etiology of OSCC is complex and involves many factors. The most clearly defined potential factors are smoking and alcohol, which substantially increase the risk of OSCC. However, despite this clear association, a substantial proportion of patients develop OSCC without exposure to them, emphasizing the role of other risk factors such as genetic susceptibility and oncogenic viruses. Some viruses are strongly associated with OSCC while the association of others is less frequent and may depend on cofactors for their carcinogenic effects. Therefore, the exact role of viruses must be evaluated with care in order to improve the diagnosis and treatment of OSCC. Although a viral association within a subset of OSCC has been shown, the molecular and histopathological characteristics of these tumors have yet to be clearly defined.

Tongue Cancer and Epigenetic Factors: An in-vitro Study on 298 Micro-RNAS

Oral Squamous Cell Carcinoma (OSCC) is the sixth most frequent malignant tumour. There is some evidence that tongue cancer has a higher local failure rate and poorer prognosis than other anatomical sites in the oral cavity. We used tongue squamous cell carcinoma cell lines harbouring mutated p53/p16 as tongue cancer models to study the influences exerted by p53 and p16 genes on the expression of micro RNAs (miRNAs). The study was performed on microarray chips harbouring 298 miRNA sequences. OSCC cell lines used in this study were SCC-4, SCC-15 and SCC-25, all three carrying mutated/hypermethylated p53/p16. The expression values normalized to healthy control of 298 miRNAs were obtained for each cell line. MiRNA 196b was found hyperexpressed in the three cell lines. MiRNAs 19b-1, 21, 27a, 30d, 134, 339, 379 and 465 were found altered in two out of three cell lines. miRNAs found altered in one cell line out of three were: 7b, 23a, 25, 30c, 30e-3p, 107,125b, 124a, 214, 216, 325 and 384. A literature review for each miRNA found significant was undertaken. Some miRNAs have a well-known role in oral cancer, some have been put in correlation with other cancers/diseases, others are found significant for the first time. These early results in tongue cancer cell lines harbouring mutation of p16/p53 need further analyses to understand whether this variation of miRNA levels are directly influenced by the malfunction of these proteins or if, vice-versa, altered miRNA levels influence the function of p16 and p53.

Role of human papillomavirus in the pathogenesis of oral squamous cell carcinoma

Oral cancer is one of the most common cancers and it constitutes a major health problem particularly in developing countries. Oral squamous cell carcinoma (OSCC) represents the most frequent of all oral neoplasms. Several risk factors have been well characterized to be associated with OSCC with substantial evidences. While tobacco and alcohol are the primary risk factors for OSCC development, many epidemiological studies report a strong association with human papillomavirus (HPV) in a subset of OSCC. This article presents our current knowledge on the relationship between HPV and development of OSCC. HPVs are DNA viruses that specifically target the basal cells of the epithelial mucosa. Most experimental data are consistent with the hypothesis that HPV plays a causal role in oral carcinogenesis. Genotypes, such as HPV1 infect epidermal cells, whereas HPV6, 11, 16 and 18 infect epithelial cells of the oral cavity and other mucosal surfaces. Several studies have shown that there is an increased risk of head and neck cancer in the two major HPV 16 oncogenes E6 and E7 -positive patients. The presence of antibodies to HPV E6 and E7 proteins was found to be more associated with tumors of the oro-pharynx than of the oral cavity. However, HPV alone appears to be insufficient as the cause of OSCC but requires other co-factors. Although a viral association within a subset of OSCC has been shown, the molecular and histopathological characteristics of these tumors have yet to be clearly defined.

Integrative mRNA profiling comparing cultured primary cells with clinical samples reveals PLK1 and C20orf20 as therapeutic targets in cutaneous squamous cell carcinoma

Identifying therapeutic targets for cancer treatment relies on consistent changes within particular types or sub-types of malignancy. The ability to define either consistent changes or sub-types of malignancy is often masked by tumor heterogeneity. To elucidate therapeutic targets in cutaneous squamous cell carcinoma (cSCC), the most frequent skin neoplasm with malignant potential, we have developed an integrated approach to gene expression profiling beginning with primary keratinocytes in culture. Candidate drivers of cSCC development were derived by first defining a set of in vitro cancer genes and then comparing their expression in a range of clinical data sets containing normal skin, cSCC and the benign hyper-proliferative condition psoriasis. A small interfering RNA (siRNA) screen of the resulting 21 upregulated genes has yielded targets capable of reducing xenograft tumor volume in vivo. Small-molecule inhibitors for one target, Polo-like kinase-1 (PLK1), are already in clinical trials for other malignancies, and our data show efficacy in cSCC. Another target, C20orf20, is identified as being overexpressed in cSCC, and siRNA-mediated knockdown induces apoptosis in vitro and reduces tumor growth in vivo. Thus, our approach has shown established and uncharacterized drivers of tumorigenesis with potent efficacy as therapeutic targets for the treatment of cSCC.

Co-overexpression of Bag-1 and heat shock protein 70 in human epidermal squamous cell carcinoma: Bag-1-mediated resistance to 5-fluorouracil-induced apoptosis

Background:

The aim was to determine whether Bcl-2-associated athanogene-1 (Bag-1) and/or its binding protein heat shock protein-70 (Hsp70) exhibit deregulated expression in epidermal squamous cell carcinoma (SCC) and whether Bag-1 confers apoptosis resistance.

Method:

Immunohistochemistry for Bag-1 and Hsp70 was performed on 60 epidermal SCC and 10 normal skin samples. The epidermal SCC cell line SCC-13 was treated with 5-fluorouracil (5-FU) after Bag-1 knockdown to determine whether high Bag-1 levels contribute to growth and/or apoptosis resistance.

Results:

Normal epithelium expressed primarily nuclear Bag-1. Most tumours showed reduced nuclear Bag-1 staining, but a subset exhibited strong Bag-1 staining, with cytoplasmic Bag-1 staining intensity correlating with cytoplasmic Hsp70 staining intensity (r_s=0.462; P<0.001) and less differentiation (P<0.001). Bag-1 knockdown resulted in markedly reduced SCC-13 cell yield, increased spontaneous apoptosis and enhanced sensitivity to 5-FU-induced apoptosis. Apoptosis induced by 5-FU in the Bag-1-knockdown cells was significantly greater than the additive apoptotic effect of 5-FU or Bag-1 knockdown alone.

Conclusions:

Overexpression of Bag-1 and Hsp70 in poorly differentiated SCC may confer both enhanced tumour cell growth and apoptosis resistance. Bag-1 may contribute to the resistance of more advanced epidermal SCC to chemotherapy.

The role of human papillomavirus in the pathogenesis of head & neck squamous cell carcinoma: an overview

Cancer statistics report an increased incidence of OSCC and OPSCC around the world. Though improvements in screening and early diagnosis have dramatically reduced the incidence of this neoplasm in recent years, the 5-year-disease-free survival, is still poor, specially for oropharyngeal cancer, despite the great scientific and financial efforts. Recently, several papers showed that HPV may be involved at least in the pathogenesis of a subgroup of oral and cervical SCC, leading to distinct molecular characteristics compared with HPV-negative ones. Nevertheless, OPSCCs associated with HPV infection seem to show a better prognosis and affect younger patients (< 40 yrs.), especially females. Therefore, there is the need to properly assess oropharyngeal SCC subgroups: 1) not HPV associated/classic oral SCC: less responsive to anticancer drugs: needs novel post-surgical treatment; 2) HPV associated/oral SCC: needs several management options and suitable "target" therapy against the virus, and/or immune-stimulating therapy. Further issues are: 1) the disclosure of putative targets for more efficient molecular therapy, which may work as cervical cancer post-surgical treatment, in anticipation of the effects of "global prevention" performed by WHO anti-HPV vaccination programs; 2) careful identification of precancerous lesions in both sites; dysplasia is currently treated by excisional or ablative procedures, which don't consider the concept of field carcinogenesis. In fact, it is probable that near or far from an excised precancerous lesion new foci of cell transformation may exist, which are not yet macroscopically evident, but, if detected, would put the patient into a high risk subgroup.Comparing findings reported in the recent literature, the data of this state of the art about HPV might add useful informations concerning oropharyngeal carcinogenesis. Moreover, our review would be useful in order to define novel perspectives of treatment choice for Head & Neck cancer patients, by combining well known chemotherapeutical drugs with new molecular "target" therapy.

Prognostic implications of miR-16 expression levels in resected non-small-cell lung cancer

BACKGROUND

MicroRNAs are novel regulators of gene expression that are linked to the main oncogene networks, including the p53 pathway. p53 regulates the maturation process of miR-16 and miR-143. We analyzed the role as prognostic markers of miR-16 and miR-143 in 70 non-small-cell lung cancer (NSCLC) patients.

METHODS

MicroRNAs were analyzed by TaqMan MicroRNA assays. Disease-free survival (DFS) and overall survival (OS) were examined using Kaplan-Meier curves with log-rank tests and the Cox proportional hazard model.

RESULTS

When patients were classified in three groups according to their miR-16 expression levels, those with normal levels had the best outcome while those with high levels had the worst. DFS was 22.4 months for patients with high levels, 71.8 months for those with normal levels, and 55.8 months for those with low levels (P = 0.05). OS was 23.9 months for patients with high levels, 97.6 months for those with normal levels, and 63.5 months for those with low levels (P < 0.001). In the multivariate analyses, high miR-16 levels emerged as an independent prognostic factor for poor DFS (P = 0.001) and OS (<0.001).

CONCLUSIONS

Our results provide the first hints that miR-16 levels in tumor samples may be a prognostic marker in NSCLC.

Opposing roles for calcineurin and ATF3 in squamous skin cancer

Calcineurin inhibitors such as cyclosporin A (CsA) are the mainstay of immunosuppressive treatment for organ transplant recipients. Squamous cell carcinoma (SCC) of the skin is a major complication of treatment with these drugs, with a 65–100 fold higher risk than in the normal population1. By contrast, the incidence of basal cell carcinoma (BCC), the other major keratinocyte-derived tumour of the skin, of melanoma and of internal malignancies increases to a significantly lesser extent 1. Here we report that genetic and pharmacological suppression of calcineurin/NFAT function promotes tumour formation in mouse skin and in xenografts, in immune compromised mice, of H-ras^V12 expressing primary human keratinocytes or keratinocyte-derived SCC cells. Calcineurin/NFAT inhibition counteracts p53-dependent cancer cell senescence thereby increasing tumourigenic potential. ATF3, a member of the “enlarged” AP-1 family, is selectively induced by calcineurin/NFAT inhibition, both under experimental conditions and in clinically occurring tumours, and increased ATF3 expression accounts for suppression of p53-dependent senescence and enhanced tumourigenic potential. Thus, intact calcineurin/NFAT signalling is critically required for p53 and senescence-associated mechanisms that protect against skin squamous cancer development.

Enhanced death ligand-induced apoptosis in cutaneous SCC cells by treatment with diclofenac/hyaluronic acid correlates with downregulation of c-FLIP

Actinic keratosis (AK) occurs on sun-exposed skin and may progress to invasive squamous cell carcinoma (SCC). As for its topical treatment, diclofenac/hyaluronic acid (HA) has been recently approved. The NSAID diclofenac is an inhibitor of COX-2; however, its mode of action in cutaneous epithelial cancer cells is largely unknown. Here, the effects of diclofenac/HA were investigated in relation to death ligand-mediated apoptosis (TNF-alpha, TRAIL, and CD95 activation). Whereas diclofenac/HA only moderately induced apoptosis by itself, it resulted in pronounced enhancement of death ligand-mediated apoptosis in sensitive SCC cell lines (3/4). Apoptosis was associated with activation of initiator caspases of the extrinsic pathway (caspase-8/caspase-10). Furthermore, death ligand and diclofenac/HA-mediated apoptosis were blocked by the same caspase inhibitors, indicating related pathways. The proapoptotic effects of diclofenac/HA appeared independent of the p53 pathway. Also, upregulation of death receptors appeared less important; however, strong downregulation of c-FLIP isoforms was seen after diclofenac/HA treatment. The crucial role of c-FLIP was proven through overexpression and knockdown experiments. Thus, induction of apoptosis appears to be highly characteristic of the mode of action of diclofenac/HA, and the therapeutic effect may be related to sensitization of neoplastic keratinocytes for death ligand-induced apoptosis.

HPV & head and neck cancer: a descriptive update

The incidence of head and neck squamous cell carcinoma (HNSCC) has been gradually increasing over the last three decades. Recent data have now attributed a viral aetiology to a subset of head and neck cancers. Several studies indicate that oral human papillomavirus (HPV) infection is likely to be sexually acquired. The dominance of HPV 16 in HPV+ HNSCC is even greater than that seen in cervical carcinoma of total worldwide cases. Strong evidence suggests that HPV+ status is an important prognostic factor associated with a favourable outcome in head and neck cancers.

Approximately 30 to 40% of HNSCC patients with present with early stage I/II disease. These patients are treated with curative intent using single modality treatments either radiation or surgery alone. A non-operative approach is favored for patients in which surgery followed by either radiation alone or radiochemotherapy may lead to severe functional impairment. Cetuximab, a humanized mouse anti-EGFR IgG1 monoclonal antibody, improved locoregional control and overall survival in combination with radiotherapy in locally advanced tumours but at the cost of some increased cardiac morbidity and mortality.

Finally, the improved prognosis and treatment responses to chemotherapy and radiotherapy by HPV+ tumours may suggest that HPV status detection is required to better plan and individualize patient treatment regimes.

Telomere dysfunction is related to the intrinsic radio-resistance of human oral cancer cells

Evidence from telomerase-deficient mice strongly suggests that dysfunctional short telomeres affect cellular radio-sensitivity but this idea has yet to be extensively tested in relevant human cancer types such as oral squamous cell carcinomas (OSCCs), which are frequently treated by radiotherapy. The OSCC line BICR7 has low levels of telomerase activity, short telomeres and high levels of telomere dysfunction (judged by a high level of anaphase bridges); whereas the BICR6 line has high levels of telomerase and is more radio-resistant. Ectopic expression of the human TElomerase Reverse Transcriptase (hTERT) reduced telomere dysfunction and increased radio-resistance in BICR7 cells, but not BICR6. Furthermore, the radio-resistance of GM847 cells, which use telomerase-independent mechanisms of telomere maintenance, and of telomerase-negative normal human fibroblasts with long telomeres are similarly unaffected by ectopic expression of telomerase. We tested whether telomere function, as measured by the Anaphase Bridge Index (ABI), was found to be a useful predictor of radio-resistance in a panel of OSCC lines. Using inverse regression analysis, we found a strong inverse relationship between the ABI and radio-resistance (P<0.001), as measured by the Surviving Fraction at 4Gy (SF4). These results suggest that telomerase inhibitors could sensitise a subset of oral SCCs with short telomeres to radiotherapy and for the first time demonstrate that the tumour ABI may assist the selection of cancers that would be suitable for such sensitisation therapy.

Divergent routes to oral cancer

Most head and neck squamous cell carcinoma (HNSCC) patients present with late-stage cancers, which are difficult to treat. Therefore, early diagnosis of high-risk premalignant lesions and incipient cancers is important. HNSCC is currently perceived as a single progression mechanism, resulting in immortal invasive cancers. However, we have found that approximately 40% of primary oral SCCs are mortal in culture, and these have a better prognosis. About 60% of oral premalignancies (dysplasias) are also mortal. The mortal and immortal tumors are generated in vivo as judged by p53 mutations and loss of p16(INK4A) expression being found only in the original tumors from which the immortal cultures were derived. To investigate the relationships of dysplasias to SCCs, we did microarray analysis of primary cultures of 4 normal oral mucosa biopsies, 19 dysplasias, and 16 SCCs. Spectral clustering using the singular value decomposition and other bioinformatic techniques showed that development of mortal and immortal SCCs involves distinct transcriptional changes. Both SCC classes share most of the transcriptional changes found in their respective dysplasias but have additional changes. Moreover, high-risk dysplasias that subsequently progress to SCCs more closely resemble SCCs than nonprogressing dysplasias. This indicates for the first time that there are divergent mortal and immortal pathways for oral SCC development via intermediate dysplasias. We believe that this new information may lead to new ways of classifying HNSCC in relation to prognosis.

Radiation response and cell cycle regulation of p53 rescued malignant keratinocytes

Mutations in the tumor suppressor gene p53 were found in more than 90% of all human squamous cell carcinomas (SCC). To study the function of p53 in a keratinocyte background, a tetracycline-controlled p53 transgene was introduced into a human SCC cell line (SCC15), lacking endogenous p53. Conditional expression of wild-type p53 protein upon withdrawal of tetracycline was accompanied with increased expression of p21(WAF1/Cip1) resulting in reduced cell proliferation. Flow-cytometric analysis revealed that these cells were transiently arrested in the G1/S phase of the cell cycle. However, when SCC15 cells expressing p53 were exposed to ionizing radiation (IR), a clear shift from a G1/S to a G2/M cell cycle arrest was observed. This effect was greatly depending on the presence of wild-type p53, as it was not observed to the same extent in SCC15 cells lacking p53. Unexpectedly, the p53- and IR-dependent G2/M cell cycle arrest in the keratinocyte background was not depending on increased expression or stabilization of 14-3-3sigma, a p53-regulated effector of G2/M progression in colorectal cancer cells. In keratinocytes, 14-3-3sigma (stratifin) is involved in terminal differentiation and its cell cycle function in this cell type might diverge from the one it fulfills in other cellular backgrounds.

Profiling early head and neck cancer

Head and neck squamous-cell carcinoma (HNSCC) is the sixth most common cancer worldwide and, disappointingly, survival rates are not improving. Moreover, HNSCC has a severe impact on the quality of life of patients and survivors, and the significant morbidity subsequent to treatment often mandates long-term multidisciplinary care, which places significant financial pressures on the treating institution. Therefore, prevention and early diagnosis of high-risk pre-malignant lesions are high priorities for reducing deaths due to head and neck cancer. Recent advances have begun to elucidate the different aetiologies of HNSCCs in relation to previous pre-malignancies and to identify which pre-malignant lesions are likely to progress to malignancy.

Histone deacetylase inhibitors induce a senescence-like state in human cells by a p16-dependent mechanism that is independent of a mitotic clock

We show here that histone deacetylase inhibitors (HDACIs) sodium dibutyrate (SDB) and trichostatin A (TSA) induce a phenotype that has similarities to replicative senescence in human fibroblasts. There was no evidence that SDB accelerated a constitutive cell division counting mechanism as previously suggested because cells pretreated with SDB for three mean population doublings (MPDs) exhibited a similar overall proliferative life span to controls once SDB was withdrawn. SDB-treated cells upregulated the cell cycle inhibitors p21(WAF1) and p16(INK4A), but not p14(ARF), in the same sequential order as in senescence and the cells developed biochemical markers of senescence. However, the mechanism of senescence did not involve telomere dysfunction and there was no evidence for any posttranslational modification of p53. The expression of human papillomavirus (HPV) 16 E6 in human fibroblasts or targeted disruption of the p53 and p21(WAF) genes only weakly antagonized HDACI-induced senescence. However, expression of the E7 gene, which inhibits the function of pRb, cooperated with E6 to block SDB-induced senescence completely and human cells deficient in p16(INK4A) (but not p14(ARF)) were also resistant to SDB-induced senescence, suggesting that the p16(INK4A)/pRb pathway is the major mediator of HDACI-induced senescence in human cells. However, p53-/- mouse fibroblasts were resistant to HDACI-induced senescence, identifying p53 as the major pathway to senescence in this species.

Genome-wide comparison of human keratinocyte and squamous cell carcinoma responses to UVB irradiation: implications for skin and epithelial cancer

To gain insight into the transformation of epidermal cells into squamous carcinoma cells (SCC), we compared the response to ultraviolet B radiation (UVB) of normal human epidermal keratinocytes (NHEK) versus their transformed counterpart, SCC, using biological and molecular profiling. DNA microarray analyses (Affymetrix), approximately 12000 genes) indicated that the major group of upregulated genes in keratinocytes fall into three categories: (i). antiapoptotic and cell survival factors, including chemokines of the CXC/CC subfamilies (e.g. IL-8, GRO-1, -2, -3, SCYA20), growth factors (e.g. HB-EGF, CTGF, INSL-4), and proinflammatory mediators (e.g. COX-2, S100A9), (ii). DNA repair-related genes (e.g. GADD45, ERCC, BTG-1, Histones), and (iii). ECM proteases (MMP-1, -10). The major downregulated genes are DeltaNp63 and PUMILIO, two potential markers for the maintenance of keratinocyte stem cells. NHEK were found to be more resistant than SCC to UVB-induced apoptosis and this resistance was mainly because of the protection from cell death by secreted survival factors, since it can be transferred from NHEK to SCC cultures by the conditioned medium. Whereas the response of keratinocytes to UVB involved regulation of key checkpoint genes (p53, MDM2, p21(Cip1), DeltaNp63), as well as antiapoptotic and DNA repair-related genes - no or little regulation of these genes was observed in SCC. The effect of UVB on NHEK and SCC resulted in upregulation of 251 and 127 genes, respectively, and downregulation of 322 genes in NHEK and 117 genes in SCC. To further analyse these changes, we used a novel unsupervised coupled two-way clustering method that allowed the identification of groups of genes that clearly partitioned keratinocytes from SCC, including a group of genes whose constitutive expression levels were similar before UVB. This allowed the identification of discriminating genes not otherwise revealed by simple static comparison in the absence of UVB irradiation. The implication of the changes in gene profile in keratinocytes for epithelial cancer is discussed.

Regional analysis of p53 mutations in rheumatoid arthritis synovium

The p53 tumor suppressor protein plays a central role in cell cycle regulation, DNA repair, and apoptosis. Recent studies indicate that DNA damage and somatic mutations in the p53 gene can occur because of genotoxic stress in many tissues, including the skin, colon, and synovium. Although somatic mutations in the p53 gene have been demonstrated in rheumatoid arthritis (RA) synovial tissue and synoviocytes, no information is available on the location or extent of p53 mutations. Using microdissected RA synovial tissue sections, we observed abundant p53 transition mutations, which are characteristic DNA damage caused by oxidative stress. p53 mutations, as well as p53 mRNA expression, were located mainly in the synovial intimal lining rather than the sublining (P < 0.01). Clusters of p53 mutant subclones were observed in some microdissected regions, suggesting oligoclonal expansion. Because IL-6 gene expression is regulated by wild-type p53, IL-6 mRNA expression in microdissected tissues was quantified by using real-time PCR. The regions with high rates of p53 mutations contained significantly greater amounts of IL-6 mRNA compared with the low mutation samples (P < 0.02). The microdissection findings suggest that p53 mutations are induced in RA synovial tissues by inflammatory oxidative stress. This process, as in sun-exposed skin and inflamed colonic epithelium, provides some of the mutant clones with a selective growth advantage. A relatively low percentage of cells containing p53 mutations can potentially affect neighboring cells and enhance inflammation through the elaboration of proinflammatory cytokines.

UV-B-type mutations and chromosomal imbalances indicate common pathways for the development of Merkel and skin squamous cell carcinomas

Two developmentally highly divergent nonmelanoma skin cancers, the epidermal squamous cell carcinomas (SCC) and the neuroendocrine Merkel cell carcinomas (MCC), occur late in life at sun-exposed body sites. To determine whether these similarities may indicate common genetic alterations, we studied the genetic profile of 10 MCCs and analyzed 6 derived cell lines and 5 skin SCC lines by comparative genomic hybridization (CGH) and molecular genetic analyses. Although the MCCs were highly divergent-only 3 of the 10 tumors exhibited common gains and losses-they shared gain of 8q21-q22 and loss of 4p15-pter with the genetically much more homogeneous SCC lines. In addition, 2 of 5 SCC and 2 of 6 MCC lines exhibited UV-B-type-specific mutations in the p53 tumor-suppressor gene and a high frequency (9/11) of CC-->TT double base changes in codon 27 of the Harvey (Ha)-ras gene. Since 45% of the tumor lines were homozygous for this nucleotide substitution compared to 14% of the controls and in 1 MCC patient the wild-type allele was lost in the tumor, this novel polymorphism may contribute to tumor development. On the other hand, loss of 3p, characteristic for SCCs, was rare in MCCs. Although in 2 of 3 SCC lines 3p loss was correlated with reduced expression of the FHIT (fragile histidine triad) gene, the potential tumor suppressor mapped to 3p14.2 and 2 MCC lines with normal 3p showed aberrant or no FHIT transcripts. Taken together, in addition to the common UV-B-specific mutations in the p53 and Ha-ras gene, MCCs and SCCs also share chromosomal imbalances that may point to a common environmental-derived (e.g., UV-A) oxidative damage.

TGF-beta1 acts as a tumor suppressor of human malignant keratinocytes independently of Smad 4 expression and ligand-induced G(1) arrest

This study examined the role of TGF-beta1 in human keratinocyte malignancy. Two carcinoma-derived human oral keratinocyte cell lines, BICR 31 and H314, were selected on the basis of their known resistance to TGF-beta1-induced G(1) arrest, the presence of wild type TGF-beta cell surface receptors and normal Ras. Smad 4 protein was undetectable in both cell lines, but Smad 2 and Smad 3 were expressed at levels comparable with a fully TGF-beta responsive cell line, and treatment of the cells with TGF-beta1 resulted in the phosphorylation of Smad 2. Treatment with exogenous TGF-beta1 resulted in a failure to induce transcription from an artificial Smad-dependent promoter and a failure to down-regulate c-myc, but resulted in an up-regulation of AP-1 associated genes (Fra-1, JunB and fibronectin). Transient transfection of Smad 4 into BICR 31 restored TGF-beta1-induced growth inhibition and Smad-dependent transcriptional activation. Protracted treatment of cells with exogenous TGF-beta1 resulted in the attenuation of cell growth in vitro. To over-express TGF-beta1, both cell lines were transfected with latent TGF-beta1 cDNA; neutralization studies of conditioned media demonstrated that whilst the majority of the peptide was in the latent form, a small proportion was present as the active peptide. Cells that over-expressed endogenous TGF-beta1 grew more slowly in vitro compared to both the vector-only controls and cells that did not over-express the peptide. Orthotopic transplantation of cells that over-expressed endogenous TGF-beta1 to the floor of the mouth in athymic mice resulted in marked inhibition of primary tumor formation compared to controls. Expression of a dominant-negative TGF-beta type II receptor in cells that over-expressed endogenous TGF-beta1 resulted in enhanced cell growth in vitro and diminished the tumor suppressor effect of the ligand in vivo, indicating that the endogenous TGF-beta1 was acting in an autocrine capacity. The results demonstrate that over-expression of endogenous TGF-beta1 in human malignant oral keratinocytes leads to growth inhibition in vivo and tumor suppression in vitro by mechanisms that are independent of Smad 4 expression and TGF-beta1-induced G(1) arrest.

Human fibroblast replicative senescence can occur in the absence of extensive cell division and short telomeres

Ectopic expression of telomerase blocks both telomeric attrition and senescence, suggesting that telomeric attrition is a mitotic counting mechanism that culminates in replicative senescence. By holding human fibroblast cultures confluent for up to 12 weeks at a time, we confirmed previous observations and showed that telomeric attrition requires cell division and also, that senescence occurs at a constant average telomere length, not at a constant time point. However, on resuming cell division, these long-term confluent (LTC) cultures completed 15-25 fewer mean population doublings (MPDs) than the controls prior to senescence. These lost divisions were mainly accounted for by slow cell turnover of the LTC cultures and by permanent cell cycle exit of 94% of the LTC cells, which resulted in many cell divisions being unmeasured by the MPD method. In the LTC cultures, p27(KIP1) accumulated and pRb became under-phosphorylated and under-expressed. Also, coincident with permanent cell cycle exit and before 1 MPD was completed, the LTC cultures upregulated the cell cycle inhibitors p21(WAF) and p16(INK4A) but not p14(ARF) and developed other markers of senescence. We then tested the relationship between cell cycle re-entry and the cell cycle-inhibitory proteins following subculture of the LTC cultures. In these cultures, the downregulation of p27(KIP1) and the phosphorylation of pRb preceded the complete resumption of normal proliferation rate, which was accompanied by the down-regulation of p16(INK4A). Our results show that most normal human fibroblasts can accumulate p16(INK4A), p21(WAF) and p27(KIP1) and senesce by cell division-independent mechanism(s). Furthermore, this form of senescence likely requires p16(INK4A) and perhaps p27(KIP1).

Overexpression of p53-related proteins predicts rapid growth rate of head and neck cancer

OBJECTIVES/HYPOTHESIS

The p53 tumor suppressor gene plays an important role for cell cycle regulation and is the most frequent mutated gene in head and neck cancer. Controversy remains regarding the biological and clinical value of immunohistochemical identification of the proteins accumulated in association with inactivation of the p53 gene and increased tumor growth. Therefore, the objective of the present study was to perform a cell kinetic analysis of cases with untreated squamous cell carcinoma and to compare the result with immunostaining for p53-related proteins in the tumor cells.

STUDY DESIGN

A prospective series of 32 patients presenting with various stages of untreated squamous cell carcinoma of the head and neck were included. Bromodeoxyuridine (BrdU) was injected as a tracer dose before tumor biopsy for cell kinetic analysis, and p53 protein accumulation was detected using two antibodies (DO7 and PAb 1801).

RESULTS

Antibody DO7 showed the highest and the optimal immunoreactivity. Diploid tumors were found in 27 cases (84%), and the mean potential doubling time (Tpot) was 55 +/- 7 hours for these tumors. Positivity of DO7 (>1%) was demonstrated in 85% of the cases. However, a discrimination level exceeding 20% was required to obtain a significant negative relationship (Spearman's rank correlation coefficient test, P < or = .03) between Tpot and DO7 positivity. At that level, 33% of the tumors remained DO7-positive. The corresponding Tpot was not significantly different from the overall mean. The rates of metastatic disease and survival were not dependent on DO7 immunoreactivity or cancer cell kinetics.

CONCLUSION

Accumulation of p53-related proteins is associated with an unrestrained growth of head and neck cancer.

Induction of apoptosis in head-and-neck squamous carcinoma cells by gamma-irradiation and bleomycin is p53-independent

We have examined the ability of gamma-irradiation and bleomycin to induce apoptosis in a model system consisting of cell lines derived from naturally occurring human head-and-neck squamous-cell carcinomas with contrasting p53 status and expression levels of pro- and anti-apoptotic molecules. Following exposure to gamma-irradiation (20 Gy) or bleomycin (3.5 microM) for 0 to 96 hr, cells expressing either transcriptionally inactive mutant p53 (HN6) or a truncated p53 molecule (HN19) underwent apoptosis, as assessed by fluorescence-activated cell sorting and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling, in contrast to cells that express wild-type p53 (HN30), suggesting that apoptosis induced by these agents occurs by p53-independent mechanisms. Apoptosis in HN6 and HN19 cells was preceded by a G(2)/M cell-cycle block, as analyzed by DNA content and BrdU staining. In contrast, HN30 cells remained blocked in both G(1) and G(2)/M and failed to re-enter the cell cycle. Levels of Bcl-2 were elevated in 3 of 10 cell lines, and only marginal differences were observed for Bcl-x(L). Pro-apoptotic proteins bax and Bcl-x(S) were detectable in normal keratinocytes and 4 tumor cell lines. Bax-delta (16 kDa) was highly represented in normal keratinocytes, and levels of bak were variable between cell lines. Elevated expression of Bcl-2 failed to protect HN19 cells from either gamma-irradiation or bleomycin-induced apoptosis. Our data support the existence of p53- and Bcl-2-independent pathways regulating apoptosis in keratinocytes and suggest that efficacy of either radiotherapy or bleomycin treatment for oral squamous-cell neoplasms may not, therefore, be influenced solely by endogenous p53 status.

Genetic aberrations in oral or head and neck squamous cell carcinoma 3: clinico-pathological applications

The molecular changes in malignant epithelium in the head and neck offer possibilities for the development of diagnostic, prognostic and other markers. This article reviews recent developments in this field.

Switch from p53 to MDM2 as differentiating human keratinocytes lose their proliferative potential and increase in cellular size

p53 transcription factor is mutated in most skin cell carcinomas and in more than 50% of all human malignancies. One of its transcriptional targets is MDM2, which in turn down-regulates p53. The role of the p53/MDM2 regulatory loop upon genotoxic stress is well documented, but less is known about its role in normal tissue homeostasis. We have explored this pathway during the different transitions of the human epidermal differentiation programme and after isolating stem cells, transit amplifying cells or differentiating cells from epidermis. Maximum expression of p53 was found in proliferating keratinocytes. A striking and transient induction of MDM2 and a down-modulation of p53 characterized the transition from proliferation to differentiation in primary human keratinocytes. These changes were delayed in late differentiating carcinoma cells, and were clearly different in suspended primary fibroblasts. Interestingly, these changes correlated with an increase in cell size, at the time of irreversible commitment to differentiation. Induction of MDM2 was also associated with suppression of proliferation in normal, or hyperproliferative, psoriatic epidermis. Moreover, both proteins were induced as keratinocytes were driven to leave the stem cell compartment by c-Myc activation. Overall, our results show a critical regulation of the p53/MDM2 pathway at the epidermal transition from proliferation to differentiation.

A proposal for the integration of immunohistochemical staining and DNA-based techniques for the determination of TP53 mutations in human carcinomas

The p53 protein plays an important role in the control of the cell cycle and DNA repair. Mutations in the TP53 gene may be a prognostic factor for certain forms of human cancer, with specific mutation sites being associated with significantly worse prognosis, particularly for colorectal and breast cancer. Thus, standardization of accurate, rapid, and cost-effective techniques for the detection of TP53 mutations is a high priority. At present, the only widely available technology that reliably detects and defines all mutations is DNA sequencing. However, the routine sequencing of the entire TP53 gene in all breast and colorectal cancer cases in hospital laboratories is prohibitively costly, complex, and time consuming. In order for the analytical power of DNA to be accessed by the routine laboratory, initial screening using immunohistochemistry, which is widely used as a test for detection of accumulated, mutated protein, followed by heteroduplex analysis of exons 4 to 9 to detect frameshift mutations in immunohistochemistry-negative cases, is proposed. To illustrate the effectiveness of this approach, 28 cases of head and neck squamous-cell carcinomas that were known to contain TP53 mutations were retrospectively analyzed. All missense mutations stained positive on immunohistochemistry using the monoclonal antibody DO7, and all insertions and deletions, even those involving a single nucleotide, were positive using an extremely simple heteroduplex analysis. Only rare nonsense mutations were not detected by this strategy. Nevertheless, application of these results to published data suggests that the prescreening would detect 80% of mutations but would result in a 75% reduction in the sequencing load of the laboratory.

P53-dependent UVB responsiveness of human keratinocytes can be altered by cultivation on cell cycle-arrested dermal fibroblasts

In cultured human keratinocytes, the tumor suppressor p53 acts as a control element in the protective response to UVB radiation and is affected by a variety of factors linked to cellular adhesion and differentiation. Because keratinocytes within the epidermis are not a homogeneous population but differ in their proliferative capacity and differentiation status, we compared the UVB responsiveness of primary keratinocyte populations isolated from various skin biopsies using p53 expression as a marker for their sensitivity to UVB. Besides keratinocytes exhibiting a UVB dose- and time-dependent upregulation of p53, keratinocyte populations were detected with high p53 expression levels even without irradiation. Such keratinocytes did not regulate p53 expression in response to UVB. Furthermore their p53-mediated UVB response was influenced by cocultivation with human dermal fibroblasts (HDF) but not with cell cycle-arrested human normal keratinocytes or HaCaT keratinocytes. When these cells were cultivated together with arrested HDF, they did not only reveal increased p53 expression levels after UVB treatment but also a more pronounced transcriptional activation of the p53 downstream target gene p21. These findings indicate that the UVB response of keratinocytes, specifically the activation of the tumor suppressor p53, is heterogeneous and can be affected by growth conditions.

ras gene mutations in oral cancer in eastern India

Oral tumor specimens (n = 50) from eastern Indian population were studied for the presence of mutations in the H-, K- and N-ras genes using selective oligodeoxynucleotide hybridization and restriction fragment length polymorphism analysis of polymerase chain reaction-amplified products. Mutations in H- and K-ras genes were observed at a frequency of 28 and 33%, respectively, whereas no N-ras mutation was noticed.

Fractional allele loss indicates distinct genetic populations in the development of squamous cell carcinoma of the head and neck (SCCHN)

Loss of heterozygosity (LOH) had been widely used to assess genetic instability in tumours and a high LOH on chromosome arms 3p, 9p and 17p has been considered to be a common event in squamous cell carcinoma of the head and neck (SCCHN). We have investigated LOH in 52 SCCHN using a range of microsatellite markers. LOH was observed in 69% of individuals on 17p using seven markers, in 64% of individuals on 3p using 17 markers and in 61% of individuals on 9p using 11 markers. Fractional allele loss (FAL) has been calculated for each tumour (FAL is the number of chromosomal arms showing LOH divided by the number of informative chromosomal arms) and a median FAL value of 0.25 was obtained in the 52 SCCHN studied. The LOH data were examined on the basis of FAL scores: low FAL (LFAL), 0.00-0.19; medium FAL (MFAL), 0.20-0.32; high FAL (HFAL), 0.33-0.88. HFAL tumours demonstrated a significantly higher LOH on chromosome arms 3p, 9p and 17p, with 94% LOH on 3p, 94% on 9p and 100% on 17p compared with LFAL tumours. Six of the 16 patients in the LFAL group were found to have no LOH on 3p, 9p or 17p and of these four had LOH at other sites, on chromosomes 2p25-p24, 5q21-22, 7pter-p22, 8q13-q22.1, 11q23.3, 13q32, 17q, 18p11.21, 18q21.31 and 19q12-q13.1. These results indicate that LFAL patients form a subset of SCCHN tumours with distinct molecular initiating events which may represent a discrete genetic population.