Although lipomas are common soft tissue tumors, few cases of lipoma or its variants have been reported in the oral cavity. We here described the clinical, histological, and immunohistochemical features of 24 cases of oral lipoma obtained from medical records at Nagasaki University Hospital between 1977 and 2010, and also retrospectively reviewed 603 cases of oral lipoma reported in the English literatures. The patients examined comprised 11 men and 13 women with a mean age of 59 years, ranging from 31 to 90 years. The main sites involved were the buccal mucosa (n = 9), followed by the tongue (n = 4), lip and retromolar area (n = 3), floor of the mouth (n = 2), and gingiva (n = 1). The mean tumor size was 2.0 cm, ranging from 0.2 to 5 cm. Histological analysis revealed 20 cases of lipoma, 2 cases of fibrolipoma, and one case each of intramuscular lipoma and spindle cell lipoma. Twenty-three cases were treated surgically while one case underwent biopsy and follow-up. Recurrence was not observed in any case. We reviewed the English literatures, and similar results were obtained. In immunohistochemical analysis, PCNA and ki-67 expression indices were higher in intramuscular lipoma cases than in its variants. Especially, it showed that a long time follow-up may be necessary in ki-67 positive cases.

Runx family proteins, Runx1, Runx2, and Runx3, play important roles in skeletal development. Runx2 is required for osteoblast differentiation and chondrocyte maturation, and haplodeficiency of RUNX2 causes cleidocranial dysplasia, which is characterized by open fontanelles and sutures and hypoplastic clavicles. Cbfb forms a heterodimer with Runx family proteins and enhances their DNAbinding capacity. Cbfb-deficient (Cbfb À/À ) mice die at midgestation because of the lack of fetal liver hematopoiesis. We previously reported that the partial rescue of hematopoiesis in Cbfb À/À mice revealed the requirement of Cbfb in skeletal development. However, the precise functions of Cbfb in skeletal development still remain to be clarified. We deleted Cbfb in mesenchymal cells giving rise to both chondrocyte and osteoblast lineages by mating Cbfb fl/fl mice with Dermo1 Cre knock-in mice. Cbfb fl/fl/Cre mice showed dwarfism, both intramembranous and endochondral ossifications were retarded, and chondrocyte maturation and proliferation and osteoblast differentiation were inhibited. The differentiation of chondrocytes and osteoblasts were severely inhibited in vitro, and the reporter activities of Ihh, Col10a1, and Bglap2 promoter constructs were reduced in Cbfb fl/fl/Cre chondrocytes or osteoblasts. The proteins of Runx1, Runx2, and Runx3 were reduced in the cartilaginous limb skeletons and calvariae of Cbfb fl/fl/Cre embryos compared with the respective protein in the respective tissue of Cbfb fl/fl embryos at E15.5, although the reduction of Runx2 protein in calvariae was much milder than that in cartilaginous limb skeletons. All of the Runx family proteins were severely reduced in Cbfb fl/fl/Cre primary osteoblasts, and Runx2 protein was less stable in Cbfb fl/fl/Cre osteoblasts than Cbfb fl/fl osteoblasts. These findings indicate that Cbfb is required for skeletal development by regulating chondrocyte differentiation and proliferation and osteoblast differentiation; that Cbfb plays an important role in the stabilization of Runx family proteins; and that Runx2 protein stability is less dependent on Cbfb in calvariae than in cartilaginous limb skeletons.

Although Akt plays key roles in various cellular processes, the functions of Akt and Akt downstream signaling pathways in the cellular processes of skeletal development remain to be clarified. By analyzing transgenic embryos that expressed constitutively active Akt (myrAkt) or dominant-negative Akt in chondrocytes, we found that Akt positively regulated the four processes of chondrocyte maturation, chondrocyte proliferation, cartilage matrix production, and cell growth in skeletal development. As phosphorylation of GSK3beta, S6K, and FoxO3a was enhanced in the growth plates of myrAkt transgenic mice, we examined the Akt downstream signaling pathways by organ culture. The Akt-mTOR pathway was responsible for positive regulation of the four cellular processes. The Akt-FoxO pathway enhanced chondrocyte proliferation but inhibited chondrocyte maturation and cartilage matrix production, while the Akt-GSK3 pathway negatively regulated three of the cellular processes in limb skeletons but not in vertebrae due to less GSK3 expression in vertebrae. These findings indicate that Akt positively regulates the cellular processes of skeletal growth and endochondral ossification, that the Akt-mTOR, Akt-FoxO, and Akt-GSK3 pathways positively or negatively regulate the cellular processes, and that Akt exerts its function in skeletal development by tuning the three pathways in a manner dependent on the skeletal part.

Recent studies suggest that cancer stem cells may be responsible for tumorigenesis and contribute to some individuals' resistance to cancer therapy. Some studies demonstrate that side population (SP) cells isolated from diverse cancer cell lines harbor stem cell-like properties; however, there are few reports examining the role of SP cells in human oral cancer. To determine whether human oral cancer cell lines contain a SP cell fraction, we first isolated SP cells by fluorescence activated cell sorting, followed by culturing in serum-free medium (SFM) using the SCC25 tongue cancer cell line, so that SP cells were able to be propagated to maintain the CSC property. Differential expression profile of stem cell markers (ABCG2, Oct-4 and EpCAM) was examined by RT-PCR in either SP cells or non-SP cells. Growth inhibition by 5-FU was determined by the MTT assay. Clonogenic ability was evaluated by colony formation assay. SCC25 cells contained 0.23% SP cells. The fraction of SP cells was available to grow in SFM cultures. SP cells showed higher mRNA expression of stem cell markers (ABCG2, Oct-4 and EpCAM) as compared with non-SP cells. Moreover, SP cells demonstrated more drug resistance to 5-FU, as compared with non-SP cells. The clone formation efficiency of SP cells was significantly higher than non-SP cells at an equal cell number (P<0.01). We isolated cancer stem-like SP cells from an oral cancer cell line. SP cells possessed the characteristics of cancer stem cells, chemoresistance, and high proliferation ability. Further characterization of cancer stem-like SP cells may provide new insights for novel therapeutic targets.

Summary. Runx2 is an essential transcription factor for bone and tooth development whose function in odontoblast differentiation remains to be clarified. To pursue this issue, we examined tooth development in Runx2 transgenic mice under the control of Col1a1 promoter (Tg(Col1a1-Runx2) mice). Endogenous Runx2 protein was detected in the nuclei of preodontoblasts, immature odontoblasts, mesenchymal cells in the dental sac, and osteoblasts, while transgene expression was detected in odontoblasts and osteoblasts. Odontoblasts in Tg(Col1a1-Runx2) mice lost their columnar shape and dentin was deposited around the odontoblasts, which were cuboid or flat in shape. The dentin in Tg(Col1a1-Runx2) mice was thin and possessed lacunae that contained odontoblasts and bone canaliculi-like structures, while predentin and Received May 7, 2008This work was supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (19592120) and the President's Discretionary Fund of Nagasaki University, Japan.Address for correspondence: Prof. Toshihisa Komori, MD, PhD, Department of Cell Biology, Unit of Basic Medical Sciences, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan Tel: +81-95-819-7630, Fax: +81-95-819-7633 E-mail: komorit@nagasaki-u.ac.jp dentinal tubules were absent. We examined the expression of dentin matrix protein genes, Col1a1 and dentin sialophosphoprotein (DSPP), by in situ hybridization, and dentin matrix proteins, osteocalcin, osteopontin, and dentin matrix protein 1 (DMP1) as well as an intermediate fi lament, nestin, by immunohistochemistry to characterize odontoblasts in Tg(Col1a1-Runx2) mice. Results showed Col1a1 expression was down-regulated, DSPP expression was lost, and nestin expression was severely decreased in the odontoblasts of Tg(Col1a1-Runx2) mice. Further, the expressions of osteocalcin, osteopontin, and DMP1 were up-regulated in odontoblasts, although the upregulation of osteocalcin expression was transient. These findings indicate that Runx2 inhibits the terminal differentiation of odontoblasts, and that Runx2 induces transdifferentiation of odontoblasts into osteoblasts forming a bone structure. Thus, Runx2 expression has to be downregulated during odontoblast differentiation to acquire full odontoblast differentiation for dentinogenesis.