Gene expression profiling of ameloblastoma and human tooth germ by means of a cDNA microarray

Expression of tumor necrosis factor alpha, TNF-related apoptosis-inducing ligand, and their associated molecules in ameloblastomas

BACKGROUND

To clarify the roles of the apoptosis signaling pathway mediated by death receptors in oncogenesis and cytodifferentiation of odontogenic tumors, expression of tumor necrosis factor alpha (TNFalpha), TNF-related apoptosis-inducing ligand (TRAIL), and their associated molecules was analyzed in ameloblastomas as well as in tooth germs.

METHODS

Tissue specimens of 10 tooth germs, 40 benign ameloblastomas, and five malignant ameloblastomas were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry to determine the expression of TNFalpha, TNF receptor I (TNFRI), TRAIL, TRAIL receptor 1 (TRAIL-R1), TRAIL-R2, caspase-8, and nuclear factor-kappaB (NF-kappaB).

RESULTS

Expression of TNFalpha, TNFRI, TRAIL, TRAIL-R1, TRAIL-R2, and NF-kappaB mRNA was detected in most samples of normal and neoplastic odontogenic tissues. Expression of caspase-8 mRNA was identified in six of 33 ameloblastomas, but not in 10 tooth germs or one malignant ameloblastoma. Immunohistochemical reactivity for TNFalpha, TRAIL, their receptors, and NF-kappaB was detected in both normal and neoplastic odontogenic tissues. Epithelial expression of TNFalpha was focal in about 50% of tooth germs and ameloblastomas, and TNFalpha expression in neoplastic cells was significantly higher in follicular ameloblastomas than in plexiform ameloblastomas. TRAIL reactivity was evident in epithelial cells neighboring the basement membrane. Receptors for TNFalpha and TRAIL were diffusely expressed in both normal and neoplastic odontogenic epithelium. Expression of caspase-8 was found in some neoplastic cells in three of 37 ameloblastomas, but not in 10 tooth germs or five malignant ameloblastomas. Nuclear NF-kappaB expression was much lower than cytoplasmic expression in both normal and neoplastic odontogenic epithelium.

CONCLUSION

Expression of TNFalpha, TRAIL, and their receptors in tooth germs and ameloblastomas suggests that these death factors might be involved in cytodifferentiation of odontogenic epithelium and tissue structuring of ameloblastomas. Expression of caspase-8 and NF-kappaB suggests that signaling of TNFalpha and TRAIL minimally affects the biological properties of odontogenic epithelial components.

Expression of p63 and p73 in ameloblastomas

BACKGROUND

To clarify the role of p53 homologs in oncogenesis and cytodifferentiation of odontogenic tumors, expression of p63 and p73 was analyzed in ameloblastomas as well as tooth germs.

METHODS

Tissue specimens of nine tooth germs and 48 benign and five malignant ameloblastomas were examined by immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) for the expression of p63 and p73.

RESULTS

Immunoreactivity for p63 and p73 was evident in epithelial cells neighboring the basement membrane in developing and neoplastic odontogenic tissues. p63 expression in desmoplastic ameloblastomas was significantly higher than in acanthomatous and granular cell ameloblastomas, and ameloblastic carcinomas showed higher p63 expression than metastasizing ameloblastomas. p73 expression was significantly higher in plexiform ameloblastomas than in follicular ameloblastomas, and basal cell ameloblastomas showed higher p73 expression than granular cell ameloblastomas. mRNA transcripts for Delta Np63 and TAp73 were detected in all developing and neoplastic odontogenic tissues. TAp63 mRNA was expressed in five of eight tooth germs, 16 of 34 ameloblastomas, and one of one malignant ameloblastoma, whereas Delta Np73 mRNA was recognized in one of eight tooth germs, nine of 34 ameloblastomas, and one of one malignant ameloblastoma.

CONCLUSION

The expression of p63 and p73 suggests that these p53 homologs play a role in differentiation and proliferation of odontogenic epithelial cells. Variations of predominantly expressed isoforms suggest that p63 and p73 might differentially function in odontogenic tissues.

Characterization of gene expression in major types of salivary gland carcinomas with epithelial differentiation

Gene expression profiles were studied in 13 cases of salivary gland carcinoma including mucoepidermoid carcinoma (MEC), acinic cell carcinoma (ACC), and salivary duct carcinoma (SDC) using a cDNA array. A total of 162 genes were deregulated. Only 5 genes were overexpressed in all carcinomas including fibronectin 1 (FN1), tissue metalloproteinase inhibitor 1 (TIMP1), biglycan (BGN), tenascin-C (HXB), and insulin-like growth factor binding protein 5 (IGFBP5), whereas 16 genes were underexpressed. The small number of similarly deregulated genes in these carcinoma entities suggests an extensive genetic variation between them. This result agrees with the great histopathological diversity of different entities of salivary gland carcinoma. Furthermore, diversity in gene expression between the carcinoma types was identified also by hierarchical clustering. Each carcinoma entity was clustered together but MEC, SDC, and ACC were separated from each other. Significance analysis of microarrays identified 27 genes expressed differently between the groups. In MEC, overexpressed genes included those of cell proliferation (IL-6 and SFN) and cell adhesion (SEMA3F and COL6A3), whereas many underexpressed genes were related to DNA modification (NTHL1 and RBBP4). Apoptosis-related genes CASP10 and MMP11 were overexpressed in SDC, in accordance with the typical tumor necrosis seen in this entity. An intermediate filament protein of basal epithelial cells, cytokeratin 14 (KRT14) was clearly differently expressed between the 3 types of carcinoma, and can be used as an aid in their differential diagnosis. The array results were validated by RT-PCR and immunohistochemistry.

The developmental relationship between the deciduous dentition and the oral vestibule in human embryos

In humans, there is no consensus about the developmental relationship between the deciduous dentition and the oral vestibule separating the teeth from the lips and cheeks. The classical concept assumes that two horseshoe-shaped epithelial structures exist: the dental lamina, giving rise to single tooth primordia, and the vestibular lamina running parallel and externally to it, giving rise to the oral vestibule. The aim of this study was to investigate the development of the dental and vestibular laminae in the upper jaw and to determine their developmental relationship in humans from embryonic week 6 to 9. Although a thickening of the vestibular epithelium was always present on serial histological sections, computer-aided three-dimensional reconstructions did not show any continuous vestibular lamina. Several discontinuous epithelial structures (bulges and ridges) occurred transiently at different stages of oral vestibule development. Along the mesiodistal axis, the dental and vestibular epithelia were regionalized in parallel: in the incisive, canine, and 1st and 2nd molar regions. The vestibular ridges fused with the dental lamina distally to the deciduous canine, 1st molar and 2nd molar. These interactions between the developing teeth and vestibular structures are reminiscent of the situation in some reptiles, where single teeth are paired one-to-one with single tooth glands.

Allelic loss of tumor suppressor genes in ameloblastic tumors

Ameloblastoma is an odontogenic tumor with a variety of histologic appearances and an unpredictable biologic behavior. Little is known about allelic losses of tumor suppressor genes in ameloblastomas. This study surveyed DNA damage in ameloblastomas and correlated this with histologic sub-type and clinical outcome. There were 12 ameloblastomas (two peripheral, eight solid, and two unicystic) and three ameloblastic carcinoma studied for loss of heterozygosity of tumor suppressor genes on chromosomes 1p, 3p, 9p,10q, and 17p (L-myc, hOGG1, p16, pten, and p53). The frequency of allelic loss and the intratumoral heterogeneity were calculated. L-myc (71% frequency of allelic loss) and pten (62% frequency of allelic loss) had the most frequent allelic losses. Overall frequency of allelic loss and intratumoral heterogeneity were higher in mandibular and in unicystic tumors and lower in tumors that recurred/metastasized. The rate of allelic loss in the three carcinomas was similar to that seen in benign tumors. The frequency of allelic loss and intratumoral heterogeneity did not correlate with age, gender, histologic subtype, or prognosis. Since tumors that behaved aggressively did not harbor more allelic losses, it is likely that DNA damage in ameloblastomas and ameloblastic carcinomas is sporadic and cumulative. We conclude that other genetic or epigenetic mechanisms may be responsible for malignant behavior in ameloblastic carcinomas.

K-Ras gene status and expression of Ras/mitogen-activated protein kinase (MAPK) signaling molecules in ameloblastomas

BACKGROUND

To clarify the roles of rat sarcoma (Ras)/mitogen-activated protein kinase (MAPK) signaling pathway in oncogenesis and cytodifferentiation of odontogenic tumors, K-Ras gene status and expression of Ras, Raf1, MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK)1, and ERK1/2 proteins were analyzed in ameloblastomas as well as in tooth germs.

METHODS

Paraffin sections of 10 tooth germs and 46 benign and 6 malignant ameloblastomas were examined immunohistochemically for the expression of K-Ras, Raf1, MEK1, and ERK1/2. Frozen tissue samples of 22 benign ameloblastomas and 1 malignant (metastasizing) ameloblastoma were analyzed by direct DNA sequencing to detect K-Ras gene alteration.

RESULTS

Immunohistochemical reactivity for K-Ras, Raf1, MEK1, and ERK1/2 was detected in both normal and neoplastic odontogenic epithelium, and these molecules were reactive chiefly with odontogenic epithelial cells neighboring the basement membrane. Plexiform ameloblastomas showed slightly stronger expression of these Ras/MAPK signaling molecules than follicular ameloblastomas. Keratinizing cells and granular cells showed decreased reactivity for the signaling molecules. Basal cell ameloblastomas showed slightly stronger reactivity for the signaling molecules than did the other subtypes. K-Ras immunoreactivity in malignant ameloblastomas was lower than that in dental lamina of tooth germs. Direct DNA sequencing showed a GGT to GCT point mutation at codon 12 of K-Ras gene in one ameloblastoma.

CONCLUSION

Expression of K-Ras, Raf1, MEK1, and ERK1/2 in tooth germs and ameloblastomas suggests that Ras/MAPK signaling pathway functions to regulate cell proliferation and differentiation in both normal and neoplastic odontogenic epithelium. K-Ras gene status implied that K-Ras mutations might play a minor role in oncogenesis of odontogenic epithelium.

mRNA expression and phenotype of odontogenic tumours in the v-Ha-ras transgenic mouse

Ameloblastomas are the most common odontogenic neoplasia in humans, and although typically considered locally invasive and benign, frequently recur subsequent to surgical resection. The Tg.AC transgenic mouse carrying the v-Ha-ras oncogene has been found to spontaneously develop ameloblastoma-like tumours (35% by 1 year of age) that are rare in the wild type FVB background strain.

OBJECTIVE

The purpose of this study was to characterise the mRNA expression of genes in the mouse tumours that are either expressed in human ameloblastomas or essential for normal odontogenesis and to correlate the expression to the histological phenotype.

STUDY METHODS

Histological, immunohistochemical and RT-PCR studies were used to evaluate clinically demonstrable odontogenic tumours occurring spontaneously in seven Tg.AC v-Ha-ras transgenic mice (homozygous, at 7 months of age or heterozygous at 11 months of age).

RESULTS

Most genes profiled were expressed in all tumour samples, however three (amelogenin, matrix metalloproteinase-20 (MMP-20) and Dlx7) displayed differential expression. In addition, only the most highly differentiated tumour stained positively for collagen. In most cases, the variable expression could be explained by reference to the histological phenotype, although differences in gene expression were apparent within the Type 2 and the mixed phenotype tumours.

CONCLUSIONS

These data confirm that many of the genes thought to be important in odontogenesis and odontogenic tumour formation in humans are also expressed in these murine ameloblastoma-like tumours however genes associated with terminal differentiation of ameloblasts demonstrate differential expression between the tumour phenotypes.

Expression of survivin and X chromosome-linked inhibitor of apoptosis protein in ameloblastomas

To clarify the role of apoptosis in oncogenesis and cytodifferentiation of odontogenic epithelium, expression of survivin and X chromosome-linked inhibitor of apoptosis protein (XIAP), inhibitor of apoptosis protein (IAP) family proteins, was examined in tooth germs and in benign and malignant ameloblastomas by means of immunohistochemistry and reverse-transcription polymerase chain reaction. Immunoreactivity for survivin and XIAP was detected in developing and neoplastic odontogenic epithelium. In tooth germs, survivin expression was evident in inner enamel epithelium. Follicular, plexiform and metastasizing ameloblastomas showed survivin reactivity chiefly in neoplastic cells neighboring the basement membrane, and most neoplastic cells in basal cell and desmoplastic ameloblastomas and ameloblastic carcinomas were positive for survivin. Survivin mRNA levels were slightly higher in ameloblastomas than in tooth germs, suggesting that elevation of survivin expression might be involved in oncogenesis of odontogenic epithelium. Immunoreactivity for XIAP was detected in most odontogenic epithelial cells in tooth germs and in benign and malignant ameloblastomas, and XIAP mRNA levels were significantly higher in follicular ameloblastomas than in plexiform ameloblastomas. The expression of survivin and XIAP in odontogenic tissues suggests that these IAP family proteins contribute to the biological properties of ameloblastomas, such as cell survival, proliferation, differentiation and tissue structuring, as well as to cellular regulation during tooth development.