The invasion of oral squamous cell carcinoma (SCC) cells into the mandibular bone is a common clinical problem. It has been reported that BHY cells, a human oral SCC cell line, are capable of invading mandibular bone of nude mice. These results led us to examine possible mechanisms of osteoclastogenesis induced by BHY cells using in vitro culture systems. When BHY cells were cocultured with mouse bone marrow cells (BMCs), only few osteoclasts were formed, even though BHY cells express the receptor activator of NF-jB ligand (RANKL). However, adding BHY cells to a coculture of mouse primary osteoblasts (POBs) and BMCs markedly induced osteoclastogenesis in the absence of osteotropic factors. Furthermore, another oral SCC cell line, HSC-2, which does not express RANKL, also induced osteoclastogenesis in our cocultures. These effects were significantly, but not completely, inhibited by adding osteoprotegerin (OPG). In addition, we also found that TNFa released from these cells partially contributes to osteoclastogenesis via a RANKL-independent mechanism. Adding BHY or HSC-2 cells suppressed mouse OPG mRNA expression and protein production by POBs in cocultures of POBs and human oral SCC cells. This finding is consistent with the result that BHY cells and HSC-2 cells did not enhance osteoclastogenesis in cocultures of BMCs and POBs from OPG-deficient mice. Immunohistochemical analysis showed a reduction of OPG expression in osteolytic lesions as compared to normal lesions from oral SCC patients. Therefore, oral SCC-induced suppression of OPG expression in POBs appears critical for osteoclastogenesis, rather than expression of RANKL in SCC cells. ' 2005 Wiley-Liss, Inc.Key words: squamous cell carcinoma; RANKL; OPG; osteoclastogenesis Oral cancer most commonly involves the tissue of the tongue and the lips, and it can also occur on the floor of the mouth, gingiva or plate.1,2 The vast majority of oral cancers are squamous cell carcinomas (SCCs) 1,2 and oral SCCs frequently invade the mandibular bone. Advanced oral SCC has a high mortality and treatment is complicated by the disruption of speech and swallowing after surgical resection. It is generally agreed that patients with mandibular invasion should be treated surgically, but the extent of mandibular resection required remains controversial. Resection of the mandibular bone leads to physical damage as well as frequent psychological problems for the patients.It is well known that oral SCC invades the mandibular bone by direct extension and not by metastasis.3,4 Previous studies have suggested that the bone destruction associated with carcinoma invasion is mediated by osteoclasts rather than directly by the carcinoma.3,4 Invasion of the mandible by oral SCC is currently established only by radiological inspection. The cellular and molecular mechanisms regulating bone invasion and osteoclastic bone resorption by oral SCC are poorly understood.Osteoclasts are multinucleated cells that are responsible for bone resorption. [5][6][7] Osteoclastic bone resorption consists...

Oral squamous cell carcinomas (OSCCs) are malignant tumors that frequently invade the maxilla and mandibular bone. However, the molecular mechanisms underlying bone invasion by OSCC are unclear. Recent studies showed that receptor activator of nuclear factor κB (RANK) was expressed not only in osteoclast precursors but also in tumor cells. Therefore, we examined whether RANK ligand (RANKL)/RANK signaling regulates bone invasion by OSCC cells in vivo and in vitro. We first injected human OSCC B88 cells into the masseter region of nude mice. Mice were treated for 3 weeks with osteoprotegerin (OPG), the decoy receptor for RANKL. Treatment with OPG decreased bone invasion by B88 cells, reduced the number of osteoclasts and increased B88 cell apoptosis. However, OPG did not affect apoptosis and proliferation in B88 cells in vitro, suggesting that the effects of OPG on apoptosis in B88 cells are restricted in a bone environment. RANK was expressed in the B88 cells and in OSCC cells from patients. RANKL induced NF-κB activation and extracellular signal-regulated kinase phosphorylation in B88 cells and enhanced B88 cell migration in a modified chemotaxis chamber equipped with a gelatin-coated filter. OPG inhibited RANKL-induced NF-κB activation, extracellular signal-regulated kinase phosphorylation and cell migration. Our data clearly indicate that RANKL/RANK inhibition suppresses bone invasion by inhibiting osteoclastogenesis and cancer cell migration and by inducing apoptosis of cancer cells via indirect anticancer action in vivo.

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Mucosa-associated lymphoid tissue (MALT) lymphoma is an extranodal low-grade lymphoma found mainly in the gastrointestinal tract. However, it rarely occurs in the oral cavity. A case of MALT lymphoma arising in the minor salivary glands of the buccal region is reported. A 21-year-old woman was referred to our department because of a swelling in the left buccal mucosa. Clinically, the mass was elastic hard and painless, but did not

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