RESUMEN
Enamelin (ENAM) has three putative phosphoserines (pSers) phosphorylated by a Golgi-associated secretory pathway kinase (FAM20C) based on their distinctive Ser-x-Glu (S-x-E) motifs. Fam20C-knockout mice show severe enamel defects similar to those in the Enam-knockout mice, implying an important role of the pSers in ENAM. To determine the role of pSer55 in ENAM, we characterized ENAMRgsc514 mice, in which Ser55 cannot be phosphorylated by FAM20C due to an E57>G57 mutation in the S-x-E motif. The enamel microstructure of 4-week-old mice was examined by scanning electron microscopy. The teeth of 6-day-old mice were characterized by histology and immunohistochemistry. The protein lysates of the first lower molars of 4-day-old mice were analyzed by Western immunoblotting using antibodies against ENAM, ameloblastin and amelogenin. ENAMRgsc514 heterozygotes showed a disorganized enamel microstructure, while the homozygotes had no enamel on the dentin surface. The N-terminal fragments of ENAM in the heterozygotes were detained in the ameloblasts and localized in the mineralization front of enamel matrix, while those in the WT mice were secreted out of ameloblasts and distributed evenly in the outer 1/2 of enamel matrix. Surprisingly, the ~15 kDa C-terminal fragments of ameloblastin were not detected in the molar lysates of the homozygotes. These results suggest that the phosphorylation of Ser55 may be an essential posttranslational modification of ENAM and is required for the interaction with other enamel matrix molecules such as ameloblastin in mediating the structural organization of enamel matrix and protein-mineral interactions during enamel formation.International Journal of Oral Science (2017) 9;e4; doi:10.1038/ijos.2017.41; published online 29 November 2017.
Asunto(s)
Amelogénesis/fisiología , Proteínas del Esmalte Dental/metabolismo , Esmalte Dental/metabolismo , Ameloblastos/metabolismo , Amelogénesis/genética , Amelogenina/metabolismo , Animales , Western Blotting , Esmalte Dental/ultraestructura , Inmunohistoquímica , Ratones , Ratones Noqueados , Microscopía Electrónica de Rastreo , Fosforilación , Serina/metabolismoRESUMEN
FAM20A has been studied to a very limited extent. Mutations in human FAM20A cause amelogenesis imperfecta, gingival fibromatosis and kidney problems. It would be desirable to systemically analyse the expression of FAM20A in dental tissues and to assess the pathological changes when this molecule is specifically nullified in individual tissues. Recently, we generated mice with a Fam20A-floxed allele containing the beta-galactosidase reporter gene. We analysed FAM20A expression in dental tissues using X-Gal staining, immunohistochemistry and in situ hybridization, which showed that the ameloblasts in the mouse mandibular first molar began to express FAM20A at 1 day after birth, and the reduced enamel epithelium in erupting molars expressed a significant level of FAM20A. By breeding K14-Cre mice with Fam20A(flox/flox) mice, we created K14-Cre;Fam20A(flox/flox) (conditional knock out, cKO) mice, in which Fam20A was inactivated in the epithelium. We analysed the dental tissues of cKO mice using X-ray radiography, histology and immunohistochemistry. The molar enamel matrix in cKO mice was much thinner than normal and was often separated from the dentinoenamel junction. The Fam20A-deficient ameloblasts were non-polarized and disorganized and were detached from the enamel matrix. The enamel abnormality in cKO mice was consistent with the diagnosis of amelogenesis imperfecta. The levels of enamelin and matrix metalloproteinase 20 were lower in the ameloblasts and enamel of cKO mice than the normal mice. The cKO mice had remarkable delays in the eruption of molars and hyperplasia of the gingival epithelium. The findings emphasize the essential roles of FAM20A in the development of dental and oral tissues.
Asunto(s)
Amelogénesis Imperfecta/genética , Proteínas del Esmalte Dental/fisiología , Proteínas/fisiología , Erupción Dental , Ameloblastos , Amelogénesis , Amelogénesis Imperfecta/metabolismo , Animales , Galactósidos , Humanos , Indoles , Ratones , Ratones NoqueadosRESUMEN
Our previous studies have demonstrated that Fam20C promotes differentiation and mineralization of odontoblasts, ameloblasts, osteoblasts and osteocytes during tooth and bone development. Ablation of the Fam20C gene inhibits bone and tooth growth by increasing fibroblast growth factor 23 in serum and causing hypophosphatemia in conditional knockout mice. However, control and regulation of the expression of Fam20C are still unknown. In this study, we generated a transgenic reporter model which expresses green fluorescence protein (GFP) driven by the Fam20C promoter. Recombineering was used to insert a 16 kb fragment of the mouse Fam20C gene (containing the 15 kb promoter and 1.1 kb of exon 1) into a pBluescript SK vector with the topaz variant of GFP and a bovine growth hormone polyadenylation sequence. GFP expression was subsequently evaluated by histomorphometry on cryosections from E14 to adult mice. Fluorescence was evident in the bone and teeth as early as E17.5. The GFP signal was maintained stably in odontoblasts and osteoblasts until 4 weeks after birth. The expression of GFP was significantly reduced in teeth, alveolar bone and muscle by 8 weeks of age. We also observed colocalization of the GFP signal with the Fam20C antibody in postnatal 1- and 7-day-old animals. Successful generation of Fam20C-GFP transgenic mice will provide a unique model for studying Fam20C gene expression and the biological function of this gene during odontogenesis and osteogenesis.
Asunto(s)
Proteínas de Unión al Calcio/genética , Proteínas de la Matriz Extracelular/genética , Odontogénesis/genética , Osteogénesis/genética , Animales , Proteínas Fluorescentes Verdes/genética , Células HEK293 , Humanos , Ratones , Ratones Endogámicos C57BL , Ratones TransgénicosRESUMEN
Deletion or mutation of dentin matrix protein 1 (DMP1) leads to hypophosphatemic rickets and defects within the dentin. However, it is largely unknown if this pathological change is a direct role of DMP1 or an indirect role of phosphate (Pi) or both. It has also been previously shown that Klotho-deficient mice, which displayed a high Pi level due to a failure of Pi excretion, causes mild defects in the dentinal structure. This study was to address the distinct roles of DMP1 and Pi homeostasis in cell differentiation, apoptosis and mineralization of dentin and enamel. Our working hypothesis was that a stable Pi homeostasis is critical for postnatal tooth formation, and that DMP1 has an antiapoptotic role in both amelogenesis and dentinogenesis. To test this hypothesis, Dmp1-null (Dmp1(-/-)), Klotho-deficient (kl/kl), Dmp1/Klotho-double-deficient (Dmp1(-/-)/kl/kl) and wild-type (WT) mice were killed at the age of 6 weeks. Combinations of X-ray, microcomputed tomography (µCT), scanning electron microscopy (SEM), histology, apoptosis and immunohistochemical methods were used for characterization of dentin, enamel and pulp structures in these mutant mice. Our results showed that Dmp1(-/-) (a low Pi level) or kl/kl (a high Pi level) mice displayed mild dentin defects such as thin dentin and a reduction of dentin tubules. Neither deficient mouse line exhibited any apparent changes in enamel or pulp structure. However, the double-deficient mice (a high Pi level) displayed severe defects in dentin and enamel structures, including loss of dentinal tubules and enamel prisms, as well as unexpected ectopic ossification within the pulp root canal. TUNEL assay showed a sharp increase in apoptotic cells in ameloblasts and odontoblasts. Based on the above findings, we conclude that DMP1 has a protective role for odontoblasts and ameloblasts in a pro-apoptotic environment (a high Pi level).
Asunto(s)
Amelogénesis/fisiología , Pulpa Dental/fisiología , Dentinogénesis/fisiología , Proteínas de la Matriz Extracelular/fisiología , Homeostasis/fisiología , Fosfatos/fisiología , Ameloblastos/patología , Animales , Apoptosis/fisiología , Diferenciación Celular/fisiología , Esmalte Dental/patología , Pulpa Dental/patología , Cavidad Pulpar/patología , Dentina/anomalías , Dentina/patología , Proteínas de la Matriz Extracelular/genética , Glucuronidasa/genética , Hiperfosfatemia/fisiopatología , Inmunohistoquímica , Proteínas Klotho , Ratones , Ratones Noqueados , Microscopía Electrónica de Rastreo , Odontoblastos/patología , Odontogénesis/fisiología , Osificación Heterotópica/genética , Osificación Heterotópica/patología , Calcificación de Dientes/fisiología , Microtomografía por Rayos XRESUMEN
BACKGROUND: A20, also known as tumor necrosis factor alpha induced protein 3 (TNFaip3), is a cytoplasmic zinc finger protein that inhibits nuclear factor kappa-B (NF-kappaB) activity and prevents tumor necrosis factor (TNF)-mediated programmed cell death. NF-kappaB is a transcription factor that regulates expression of genes involved in cell proliferation, cell survival and anti-apoptosis. Several studies have implicated that the NF-kappaB signal pathway is associated with angiogenesis and clinico-pathological process of adenoid cystic carcinoma (ACC) of the salivary glands. METHODS: The ability of overexpression of A20 to influence the biological behavior and invasion of ACC cells was examined. The cells were stably transfected with full-length A20 cDNA. Stable gene transfer was verified by realtime-polymerase chain reaction (PCR) and Western blot analysis. The change of cell biological behavior was examined by methyl thiazolyl tetrazolium (MTT) and NF-kappaB luciferase reporter assay and the invasion of the cells was examined by a Matrigel invasion chamber. RESULTS: pEGPFN3-A20 gene was stably transferred into ACC-2 cells and overexpressed. When cells were treated with TNFalpha, the NF-kappaB activity of ACC-2-A20 cells could be down-regulated about 46.32% in contrast to ACC-2-GFP cells (P < 0.05). A20 potently inhibited growth of A20 transfectant ACC-2-A20 compared with control vector transfected groups and the ACC-2 empty control group (P < 0.05). The ACC-2-A20 cells showed significantly reduced ability to invade through Matrigei-coated filters compared to ACC-2-GFP and ACC-2 cells. The inhibition rate was up to 71.05% (P < 0.05). CONCLUSIONS: A20 gene transfer is associated with decreased tumor invasion, in part via the down-regulation of NF-kappaB expression, providing evidence for a potential application of A20 in designing a treatment modality for salivary gland cancers such as ACC.