Establishment of human dental epithelial cell lines expressing ameloblastin and enamelin by transfection of hTERT and cdk4 cDNAs.

BACKGROUND: An in vitro cell culture system of dental epithelium is useful for the investigations of cellular differentiation and function of ameloblast in amelogenesis and of regenerative therapy in human tooth. However, there have been no immortalized human dental epithelial ameloblastic-lineage cell lines, which proliferate indefinitely and additionally produce enamel matrix proteins.
METHODS: We transfected two retroviral constructs of human telomerase reverse transcriptase (hTERT) cDNA and mouse cyclin-dependent kinase 4 (cdk4) cDNA into the primary ameloblastoma cells and isolated immortalized human dental epithelial cell lines of HAM1, HAM2 and HAM3. The three cell lines were examined by electron microscopy, assay of senescence-associated β-galactosidase activity, mRNA expression and immuno-reactivity of dental epithelial marker cell molecules and enamel matrix proteins.
RESULTS: They showed undifferentiated phenotypes in monolayer culture and did not have any β-galactosidase activity. The transcripts of dental epithelial cell markers of Msx2, Jagged1, Notch1, Sp3, Sp6, keratin 14 and keratin 18 were confirmed. In addition, mRNA and protein expression of ameloblastin and enamelin were also detected in three cell lines. All cells in the three cell lines were keratin 14- and 18-positive and some elongated cells were Jagged1-positive. Msx2-positive nuclei were noted in only HAM2 cells.
CONCLUSION: We established three cell lines by transfection of hTERT and cdk4 cDNAs, which were characterized as dental epithelial progenitor cells containing ameloblast-lineage cell phenotype.