Phosphotyrosine phosphatase activity of human periodontal ligament fibroblasts (HPLF)

: The periodontal ligament is a non-calcified connective tissue involved in the remodeling processes associated with mechanical stresses such as occlusion and mastication. This study was attempted to explore the characterization of phosphotyrosine phosphatase (PTPase) on the cell attachment and spreading of human periodontal ligament fibroblasts (HPLF). HPLF obtained by the explantation of human periodontal ligaments were cultured with vitamin D3 (D3) and dexamethasone (Dex) for 12 days. At 7 day culture, PTPase and ALPase activities were assayed with the substrates of phosphotyrosine and p-nitrophenylphosphate, respectively. Although ALPase activity of HPLF was dramatically increased by D3 and Dex, PTPase activity was not altered. After the quiescent HPLF were cultured with serum-free MCDB 107, the conditioned medium of HPLF (HPLF-CM) was coated on a hydrophobic dish. And then, HPLF were inoculated and cultured with 32Pi on the dish. PTPase activity of HPLF was decreased compared with control medium, however, the incorporation of 32Pi added in the medium was increased 2-fold. Therefore, HPLF possess the PTPase which may dephosphorylate a phosphotyrosine of phosphoproteins, which can regulate the cell proliferation. The cell attachment and spreading factors contained in HPLF-CM might alter the processes of phosphorylation and dephosphorylation of phosphoproteins.