title: Reuptake of extracellular amelogenin by dental epithelial cells results in increased levels of amelogenin mRNA through enhanced mRNA stabilization.
abstract: Amelogenin is an extracellular matrix protein secreted by ameloblasts and is a major component of enamel matrix. Recently, in addition to their role in enamel formation, the biological activity of enamel proteins in the process of cell differentiation has recently become widely appreciated. In this study, we examined the biological activity of amelogenin on ameloblast differentiation. Recombinant mouse amelogenin (rm-amelogenin) enhanced the expression of endogenous amelogenin mRNA in a cultured dental epithelial cell line (HAT-7), despite a lack of increased amelogenin promoter activity. To solve this discrepancy, we analyzed the effects of rm-amelogenin on the stability of amelogenin mRNA. The half-life of amelogenin mRNA is extremely short, but in the presence of rm-amelogenin its half-life was extended three times longer than the control. Furthermore, we showed the entry of exogenous fluorescein isothiocyanate-conjugated rm-amelogenin into the cytoplasm of HAT-7 cells. It follows from our results that exogenous amelogenin increases amelogenin mRNA levels through stabilization of mRNA in the cytoplasm of HAT-7 cells. Here we speculated that during differentiation, dental epithelial cells utilize a unique mechanism for increasing the production of amelogenin, the reuptake of secreted amelogenin.
authors.affiliation: Biomaterials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Liming
authors.initials: L
authors.lastname: Xu
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Harada
authors.forename: Tamaki
authors.initials: T
authors.lastname: Yokohama-Tamaki
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Matsumoto
authors.forename: Junzo
authors.initials: J
authors.lastname: Tanaka
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Taniguchi
mesh_terms: D020413:3' Untranslated Regions; D053523:Amelogenin; D000818:Animals; D016367:Baculoviridae / Q000378:metabolism; D015153:Blotting, Western; D002454:Cell Differentiation; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D003746:Dental Enamel Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000493:pharmacokinetics*; D004591:Electrophoresis, Polyacrylamide Gel; D004847:Epithelial Cells / Q000378:metabolism*; D007180:Incisor / Q000166:cytology; D007313:Insecta; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008855:Microscopy, Electron, Scanning; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012313:RNA / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
chemical_list: D020413:3' Untranslated Regions; D053523:Amelogenin; C507200:Amelx protein, mouse; C507201:Amelx protein, rat; D017931:DNA Primers; D018076:DNA, Complementary; D003746:Dental Enamel Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012313:RNA; D008156:Luciferases