Differential expression of Wnt ligands in different ameloblastoma subtypes suggests that the canonical and non-canonical Wnt pathways are selectively activated or repressed depending on the tumor cell differentiation status. Canonical Wnt pathway is most likely the main transduction pathway while Wnt-1 might be the key signaling molecule involved in ameloblastoma tumorigenesis.

Abstract. Oral mucosal melanoma (OMM) is a fatal sarcoma of unknown etiology. Histological morphology and genetic events are distinct from those of its cutaneous counterpart. Mutation and up-regulation of c-kit has been identified in OMM which may activate downstream molecules such as RAS and RAF. These molecules are involved in the mitogenactivated protein kinase (MAPK) pathway leading to tremendous cell proliferation and survival. NRAS and BRAF mutation and protein expression have been studied in other melanoma subtypes. The purpose of this study was to determine RAS protein expression and NRAS and BRAF mutation in 18 primary OMM cases using immunohistochemistry and mutation analysis. Results showed that RAS is intensely expressed in both in situ and invasive OMMs. However, NRAS mutation was only observed in 2/15 polymerase chain reaction (PCR) amplified cases both of which were silent mutations. On the other hand, BRAF missense mutations were observed only in 1/15 cases with PCR amplification. NRAS and BRAF mutations were independent from previously reported c-kit mutations. The classical V600E BRAF mutation was not found; instead a novel V600L was observed suggesting that the oncogenic event in OMM is different from that in skin melanoma. The low frequency of NRAS and BRAF mutations indicate that these genes are not common, but probable events in OMM pathogenesis, most likely independent of c-kit mutation. IntroductionOral mucosal melanoma (OMM) is a malignant tumor in the oral cavity characterized by adjoining proliferation of atypical melanocytes and alteration of their normal functions. Although OMM is a rare tumor observed in 0.5% of oral malignancies and 0.2-8% of all melanomas, it has an aggressive behavior with poor prognosis (1,2). Precursor lesions have not been clearly elucidated but the onset of atypical melanocytic proliferation may be the earliest indication of its development (1,3). OMM based on histological examination can be classified as in situ, invasive and the combination of both, the latter being the most commonly observed (1,4).Mitogen-activated protein kinase (MAPK) is the most common pathway described in oncogenic events during the progression of melanoma (5-8). One of the molecules that participate in this signal transduction cascade is RAS encoded by the RAS gene consisting of HRAS, KRAS and NRAS. Another molecule that leads to the activation of MAPK is RAF consisting of ARAF, BRAF and CRAF. Frequent mutations in NRAS and BRAF have been observed in cutaneous melanoma (9-11). The MAPK pathway together with the phosphoinositide 3-kinase cascade (PI3K) can be triggered by activation of c-kit leading to the recruitment of signaling proteins involved in tremendous cell proliferation and survival (12). Mutations in c-kit have been identified in mucosal melanomas rendering c-kit as a promising molecular target (13)(14)(15).NRAS and BRAF mutations have been reported in subsets of mucosal melanomas, but most reports focused on combined mucosal sites (9,(16)(17)(18)(19). Most reports have cla...

Dickkopf (Dkk)-3, an inhibitor of the Wnt/β-catenin pathway, is reported as a potential tumor suppressor gene in many cancers. To gain a better comprehension of the mechanisms involved in the carcinogenesis of oral squamous epithelium, protein expression and localization of Dkk-3 and β-catenin was investigated in normal epithelium, dysplasias and squamous cell carcinoma (SCC). An increase in β-catenin and Ki-67 expressions was observed from dysplasias to poorly differentiated SCC. Interestingly, an increase in Dkk-3 positive cells was also noted, which was correlated to the cancer progression step. A change in Dkk-3 localization during the transformation of normal oral epithelium to SCC was clearly observed. Dkk-3 was localized in the cell membrane in normal oral epithelium and in dysplasias, whereas that was localized in both cell membrane and cytoplasm in SCC. These results suggest that Dkk-3 is involved in the carcinogenesis of SCC with a distinct function from those in other cancers.

Oral squamous cell carcinoma (OSCC) is thought to arise as the result of cumulative genetic or epigenetic alterations in cancer-associated genes. We focused on the Dickkopf-3 (Dkk-3) gene as a candidate tumor suppressor in OSCC. Dkk-3 is a potential tumor suppressor, and its downregulation has been reported in various types of malignancies. However, our previous data demonstrated that the Dkk-3 protein was dominantly expressed in OSCC tissue, and its expression was correlated with a high incidence of metastasis and with poor prognosis. In order to explain this paradox, we performed functional analyses of the Dkk-3 gene in cancer cell lines. RT-PCR revealed that Dkk-3 mRNA expression was observed in OSCC-derived cell lines but not in gastrointestinal or colorectal adenocarcinoma‑derived cell lines. The siRNA for Dkk-3 was transfected into Dkk-3-expressing cells, and the changes in cell proliferation, invasion and migration were assessed. The knockdown of Dkk-3 mRNA by siRNA transfection did not affect cell proliferation, but it significantly decreased cell migration and invasion. To further investigate the precise mechanism that contributes to the potential oncogenic function of Dkk-3, the Wnt canonical pathway and non-canonical pathways were assessed. Western blotting demonstrated that the effect of Dkk-3 knockdown on cell migration or invasion was not caused by activation of the Wnt pathways. These data demonstrated that Dkk-3 expression in OSCC was different than that in adenocarcinomas. Dkk-3 may possess an oncogenic function that is independent of Wnt signaling.

Teeth are important structures for masticatory and phonetic purposes. Loss of teeth decreases these functions leading to impaired quality of life. Missing teeth replaced by tooth regeneration may be possible with emerging advances in stem cell biology and tissue engineering. Recent investigations have demonstrated that bone marrow derived cells (BMDC) can differentiate into cells other than blood cells. In the present study, the ability of BMDC to differentiate into tooth forming tissues was investigated using bone marrow transplantation model. BMDC from green fluorescent protein (GFP) transgenic mice were transplanted into 8-week old, C57BL/ 6 immunocompromised mice, which underwent 10-Gy whole body lethal irradiation. Immunohistochemical analysis revealed that bone marrow cells are positive to GFP, confirming successful bone marrow transplantation. Diffusedly GFP-positive cells were observed within the dental pulp of mouse incisor. GFP-positive cells in the dental pulp have arborescent processes resembling dendritic cell-like cells. Some odontoblast-like cells were also positive to GFP. Cells positive to GFP were observed in the cervical loop region and periodontal ligament. Langerhans cells in the oral epithelium, stromal fibroblasts, blood vessels and osteoclasts were also positive to GFP. These results indicate that BMDC have the ability to differentiate into tooth, bone and connective tissues.