Mathieu Lefeuvre

NRAS and BRAF mutation frequency in primary oral mucosal melanoma

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 mitogen-activated 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.

Deletion at Dickkopf (dkk)-3 locus (11p15.2) is related with lower lymph node metastasis and better prognosis in head and neck squamous cell carcinomas.

Head and neck squamous cell carcinoma (HNSCC) is a frequently occurring cancer, and despite improvement of its treatment methods, including chemotherapy, radiotherapy, and surgery, the improvement of survival remains poor. Recent advances in molecular biology of human cancer indicated various molecular abnormalities in HNSCC, including activation of oncogenes and inactivation of tumor suppressor genes (TSGs). Dickkopf (Dkk)-3 gene is known as a negative regulator of Wnt signaling and is suggested to function as TSG in several kinds of malignancies. We hypothesized that Dkk-3 might play an important role in HNSCC, too. Thus, in the current study, we analyzed allelic alteration of Dkk-3 locus (chromosome 11p15.2) by means of loss of heterozygosity (LOH) analysis. The study population consisted of 50 patients with HNSCC (mean age of 65 years old). Furthermore, we also examined the correlation between LOH findings of Dkk-3 locus with clinicopathological parameters to investigate its use as a biomarker in HNSCC. A remarkable LOH ratio (57%) was detected in the cases studied, implying that Dkk-3 is likely to be involved in HNSCC carcinogenesis. However, interestingly and in contrast to the expectations, we found that the group with LOH of Dkk-3 locus had less lymph node metastasis, and showed a favorable overall survival compared to the patients with retention of Dkk-3 area in survival analysis. These results indicate that Dkk-3 can play a role in HNSCC carcinogenesis with unknown mechanism. Moreover, allelic loss at Dkk-3 locus may also be used as a novel prognostic biomarker in HNSCC.

Dickkopf (Dkk)-3 and β-catenin expressions increased in the transition from normal oral mucosal to oral squamous cell carcinoma

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.

Knockdown of Dkk-3 decreases cancer cell migration and invasion independently of the Wnt pathways in oral squamous cell carcinoma‑derived cells.

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.

Fine deletion analysis of 1p36 chromosomal region in oral squamous cell carcinomas.

BACKGROUND Squamous cell carcinoma is the most common cancer type of the oral cavity and approximately 50% of the patients succumb to the disease. Unfortunately, few are known about the molecular mechanisms involving in the formation of oral squamous cell carcinoma (OSCC). Recently, it has been reported that 1p36 chromosomal region is deleted in various cancer types and is suspected to harbor various tumor suppressor genes (TSGs). However, limited studies exist on genetics alteration on 1p36 in OSCC and the responsible TSG remained unidentified. METHODS To investigate area susceptible to harbor TSG(s) involved in OSCC on 1p36 region, paired normal and tumor tissues of 27 patients with diagnosis of OSCC have been analyzed for loss of heterozygosity (LOH) using nine microsatellite markers based on recent gene mapping. RESULTS LOH was found at least in one locus in 85% of the cases (23 of 27). Interestingly, microsatellite instability was also found in 7% (two of 27) of the cases analyzed. The higher LOH frequencies were found with the markers D1S243 (25%), D1S468 (22%), D1S450 (25%), D1S228 (38%), D1S199 (28%), and D1S1676 (23%). CONCLUSIONS Three preferentially deleted regions have been identified in OSCC: region 1 (D1S468-D1S243), region 2 (D1S450-D1S228), and region 3 (D1S199-D1S1676). Multiple candidate TSGs, such as RIZ1, p73, UBE4B, Rap1GAP, EPHB2, and RUNX3, are located in these three areas. The data obtained in this study can be used for further functional analysis of these genes involved in OSCC carcinogenesis.

Establishment of odontoblastic cells, which indicate odontoblast features both in vivo and in vitro.

Tooth tissue engineering offers very attractive perspectives for elaboration of regenerative treatments, which enables to cure tooth loss and restore quality of life of the patients. To elaborate such treatment, isolation and culture of dental pulp cell must be achieved as a key element. In this article, we report the establishment of a stable cell line from GFP transgenic rat dental pulp, named TGC (Tooth Matrix-forming, GFP Rat-derived Cell). TGCs have exhibited odontoblastic feature both in vitro and in vivo. In vitro, TGC exposed to osteogenic medium demonstrated collagen fiber synthesis with matrix vesicle and mineralization and formed a sheet-like substrate on the cell culture dish. Increased ALP activity and elevated transcription level of various genes involved in calcification and dentin formation were also observed. In vivo, transplanted TGC in SCID mice with β-TCP particles formed dentin-like and pulp-like structure with lining odontoblast. Notably, even after up to 80 passages, TGCs retain their morphological features and differentiation ability. To our knowledge, this is the first report of a dental pulp-derived cell with such stable odontoblastic characteristics. TGC could be a very useful model for further study on dental pulp cell.