Cementoblastoma arising in the maxilla of an 8-year-old boy: a case report.

Cementoblastoma is an uncommon disease, representing only 1-8% of all odontogenic tumours. Furthermore, this tumour is especially uncommon in children, as only five cases have been reported in this age group. Here, we describe a case of cementoblastoma arising in the maxilla of an 8-year-old boy, that was treated with a partial maxillectomy. The patient's facial appearance has remained satisfactory, and the tumour has not recurred in the 9 years after the operation.

Exploration of tumor-suppressive microRNAs silenced by DNA hypermethylation in oral cancer.

In the last few years, microRNAs (miRNA) have started a revolution in molecular biology and emerged as key players in the carcinogenesis. They have been identified in various tumor types, showing that different sets of miRNAs are usually deregulated in different cancers. To identify the miRNA signature that was specific for oral squamous cell carcinoma (OSCC), we first examined expression profiles of 148 miRNAs in a panel of 18 OSCC cell lines and the immortalized oral keratinocyte line RT7 as a control. Compared with RT7, the expression of 54 miRNAs (36.5%) was frequently down-regulated in OSCC lines (<0.5-fold expression, >or=66.7% of 18 lines). Among these 54 miRNAs, we further analyzed four of these miRNAs (i.e., miR-34b, miR-137, miR-193a, and miR-203), located around CpG islands, to identify tumor-suppressive miRNAs silenced through aberrant DNA methylation. The expression of those four genes was restored by treatment with 5-aza-2'-deoxycytidine in OSCC cells lacking their expression. In addition, expression levels of the four miRNAs were inversely correlated with their DNA methylation status in the OSCC lines. In primary tumors of OSCC with paired normal oral mucosa, down-regulation of miRNA expression through tumor-specific hypermethylation was more frequently observed for miR-137 and miR-193a than for miR-34b and miR-203. Moreover, the ectopic transfection of miR-137 or miR-193a into OSCC lines lacking their expressions significantly reduced cell growth, with down-regulation of the translation of cyclin-dependent kinase 6 or E2F transcription factor 6, respectively. Taken together, our results clearly show that miR-137 and miR-193a are tumor suppressor miRNAs epigenetically silenced during oral carcinogenesis.

DNA polymerase eta reduces the gamma-H2AX response to psoralen interstrand crosslinks in human cells.

DNA interstrand crosslinks are processed by multiple mechanisms whose relationships to each other are unclear. Xeroderma pigmentosum-variant (XP-V) cells lacking DNA polymerase eta are sensitive to psoralen photoadducts created under conditions favoring crosslink formation, suggesting a role for translesion synthesis in crosslink repair. Because crosslinks can lead to double-strand breaks, we monitored phosphorylated H2AX (gamma-H2AX), which is typically generated near double-strand breaks but also in response to single-stranded DNA, following psoralen photoadduct formation in XP-V fibroblasts to assess whether polymerase eta is involved in processing crosslinks. In contrast to conditions favoring monoadducts, conditions favoring psoralen crosslinks induced gamma-H2AX levels in both XP-V and nucleotide excision repair-deficient XP-A cells relative to control repair-proficient cells; ectopic expression of polymerase eta in XP-V cells normalized the gamma-H2AX response. In response to psoralen crosslinking, gamma-H2AX as well as 53BP1 formed coincident foci that were more numerous and intense in XP-V and XP-A cells than in controls. Psoralen photoadducts induced gamma-H2AX throughout the cell cycle in XP-V cells. These results indicate that polymerase eta is important in responding to psoralen crosslinks, and are consistent with a model in which nucleotide excision repair and polymerase eta are involved in processing crosslinks and avoiding gamma-H2AX associated with double-strand breaks and single-stranded DNA in human cells.

gamma-H2AX formation in response to interstrand crosslinks requires XPF in human cells.

To further define the molecular mechanisms involved in processing interstrand crosslinks, we monitored the formation of phosphorylated histone H2AX (gamma-H2AX), which is generated in chromatin near double strand break sites, following DNA damage in normal and repair-deficient human cells. Following treatment with a psoralen derivative and ultraviolet A radiation doses that produce significant numbers of crosslinks, gamma-H2AX levels in nucleotide excision repair-deficient XP-A fibroblasts (XP12RO-SV) increased to levels that were twice those observed in normal control GM637 fibroblasts. A partial XPA revertant cell line (XP129) that is proficient in crosslink removal, exhibited reduced gamma-H2AX levels that were intermediate between those of GM637 and XP-A cells. XP-F fibroblasts (XP2YO-SV and XP3YO) that are also repair-deficient exhibited gamma-H2AX levels below even control fibroblasts following treatment with psoralen and ultraviolet A radiation. Similarly, another crosslinking agent, mitomycin C, did not induce gamma-H2AX in XP-F cells, although it did induce equivalent levels of gamma-H2AX in XPA and control GM637 cells. Ectopic expression of XPF in XP-F fibroblasts restored gamma-H2AX induction following treatment with crosslinking agents. Angelicin, a furocoumarin which forms only monoadducts and not crosslinks following ultraviolet A radiation, as well as ultraviolet C radiation, resulted only in weak induction of gamma-H2AX in all cells, suggesting that the double strand breaks observed with psoralen and ultraviolet A treatment result preferentially following crosslink formation. These results indicate that XPF is required to form gamma-H2AX and likely double strand breaks in response to interstrand crosslinks in human cells. Furthermore, XPA may be important to allow psoralen interstrand crosslinks to be processed without forming a double strand break intermediate.

The expression of integrin alpha(v)beta6 promotes the epithelial cell morphology and suppresses invasive behavior in transformed oral keratinocytes.

The expression of the integrin alpha(v)beta6 has been correlated with oral SCC invasion. We evaluated its expression in three 4NQO transformed murine oral keratinocyte cell lines (B7E3, B7E11 and B4B8). The B7E3 cells were negative for beta6, whereas the B7E11 and the B4B8 cells were both positive. The beta6 negative B7E3 cells were fibroblast-like in appearance, whereas the B7E11 cells were more epithelial-like. The B4B8 cells were a mixture of the two cell types. Using immunofluorescent microscopy, we found that vimentin was highly expressed in the B7E3 cells, whereas the B7E11 cells keratin positive. The B4B8 cells expressed both filaments. The B7E3 cells formed large tumors when injected into nude mice, whereas the B4B8 cells formed small tumors and the B7E11 cells formed none. These results suggest that the expression of the alpha(v)beta6 integrin suppresses tumor formation and may promote the epithelial phenotype in 4NQO-transformed murine oral keratinocytes.

Tenascin-C deposition requires beta3 integrin and Src.

In this study we now show that deposition of the mesenchymal matrix marker, tenascin-C (TN-C), is mediated through beta3 expression and activation of Src. There was a striking upregulation of TN-C matrix organization in cell lines expressing beta3 and activated Src when compared to cell lines with neither of these attributes. When beta3 function was suppressed so was the deposition of TN-C. The same was true for function and activation of Src. When Src was inactive, the deposition of TN-C was low. We also determined that one of the downstream effectors of Src, MAPK, was also required to promote TN-C deposition. When MAPK activation was inhibited, TN-C deposition was also decreased. MMP activation is also implicated in TN-C deposition. The broad spectrum MMP inhibitor, GM6001, suppressed TN-C organization. These results indicate that beta3 integrin ligand binding and the activation of the Src/MAPK/MMP pathway modulate deposition of TN-C.