Dentin sialophosphoprotein (Dspp) is mainly expressed in teeth by the odontoblasts and preameloblasts. The Dspp mRNA is translated into a single protein, Dspp, and cleaved into two peptides, dentin sialoprotein and dentin phosphoprotein, that are localized within the dentin matrix. Recently, mutations in this gene were identified in human dentinogenesis imperfecta II (Online Mendelian Inheritance in Man (OMIM) accession number 125490) and in dentin dysplasia II (OMIM accession number 125420) syndromes. Herein, we report the generation of Dspp-null mice that develop tooth defects similar to human dentinogenesis imperfecta III with enlarged pulp chambers, increased width of predentin zone, hypomineralization, and pulp exposure. Electron microscopy revealed an irregular mineralization front and a lack of calcospherites coalescence in the dentin. Interestingly, the levels of biglycan and decorin, small leucine-rich proteoglycans, were increased in the widened predentin zone and in void spaces among the calcospherites in the dentin of null teeth. These enhanced levels correlate well with the defective regions in mineralization and further indicate that these molecules may adversely affect the dentin mineralization process by interfering with coalescence of calcospherites. Overall, our results identify a crucial role for Dspp in orchestrating the events essential during dentin mineralization, including potential regulation of proteoglycan levels.

Emerging knowledge on how the dysregulated function of signaling networks contributes to the malignant growth of squamous cell carcinoma of the head and neck (HNSCC) can now be exploited to identify novel mechanism-based anticancer treatments. In this regard, we have observed that persistent activation of the serine/threonine kinase Akt is a frequent event in HNSCC, and that blockade of its upstream kinase, 3'-phosphoinositide-dependent kinase 1, potently inhibits tumor cell growth. Akt promotes cell proliferation by its ability to coordinate mitogenic signaling with energy- and nutrient-sensing pathways that control protein synthesis through the atypical serine/threonine kinase, mammalian target of rapamycin (mTOR). This kinase, in turn, phosphorylates key eukaryotic translation regulators, including p70-S6 kinase and the eukaryotic translation initiation factor, 4E binding protein 1. Indeed, we show here that aberrant accumulation of the phosphorylated active form of S6, the most downstream target of the Akt-mTOR-p70-S6 kinase pathway, is a frequent event in clinical specimens from patients with HNSCC and their derived cell lines. Of interest, this enhanced level of the phosphorylated active form of S6 was rapidly reduced in HNSCC cell lines and HNSCC xenograft models at clinically relevant doses of rapamycin, which specifically inhibits mTOR. Furthermore, we observed that rapamycin displays a potent antitumor effect in vivo, as it inhibits DNA synthesis and induces the apoptotic death of HNSCC cells, ultimately resulting in tumor regression. These findings identify the Akt-mTOR pathway as a potential therapeutic target for HNSCC, and may provide the rationale for the early clinical evaluation of rapamycin and its analogues in patients with HNSCC.

A primary objective in the treatment of periodontal diseases is the regeneration of the mineralized and soft connective tissue components of the attachment apparatus. Current theories suggest the cells of the periodontium have the capacity, when appropriately triggered, to actively participate in restoring connective tissues, including mineralized tissues. To evaluate further the role of such cells in periodontal homeostasis, periodontal ligament (PDL) cells and gingival fibroblasts (GF) were cultured and examined for alkaline phosphatase levels and for the ability to produce mineralized nodules in culture. These are two characteristics of osteoblast-like cells in vitro. The levels of alkaline phosphatase produced by these cells were determined by a modified kinetic assay and the ability of these cells to produce mineral-like nodules in vitro was evaluated by Von Kossa staining and light and electron microscopy. PDL cells had significantly higher levels of alkaline phosphatase when compared with gingival fibroblasts obtained from the same patient and the same passage, in vitro. Furthermore PDL cells, but not GF, were capable of producing mineral-like nodules in vitro. These results indicate differences in behavior between PDL cells and GF; such differences may prove important in designing appropriate clinical therapies directed at stimulating periodontal regeneration.

Squamous carcinomas of the head and neck (HNSCC) represent the sixth most common cancer among men worldwide and a major cause of morbidity and mortality due to its relatively poor prognosis. As part of ongoing studies addressing the molecular events underlying tumor progression in HNSCC, we have explored the nature of the proliferative pathways in which dysregulation may promote aberrant cell growth in this tumor type. The serine/threonine protein kinase Akt is a downstream target of phosphatidylinositol 3-kinase and a key regulator of normal and cancerous growth and cell fate decisions. Therefore, in this study, we have examined the status of activation of Akt in different stages of squamous cell carcinoma development in mice and in clinical samples from HNSCC patients. By immunohistochemical analysis, using a recently developed phosphorylation state-specific antibody, we demonstrated that Akt activation correlates closely with the progression of mouse skin squamous cell carcinoma. We also observed that activation of Akt is a frequent event in human HNSCC because active Akt can be detected in these tumors with a pattern of expression and localization correlating with the progression of the lesions. In line with these observations, Akt was constitutively activated in a large fraction of HNSCCderived cell lines. We also provide evidence that the Akt signaling pathway may represent a biologically relevant target for a novel antineoplastic agent, UCN-01, which recently has been shown to be active in cellular and xenograft models for HNSCC at concentrations safely achievable in clinically relevant situations.