Regulation of PLAP-1 expression in periodontal ligament cells.

Periodontal-ligament-associated protein-1 (PLAP-1) is preferentially expressed in the periodontal ligament (PDL) and encodes a novel small leucine-rich repeat proteoglycan protein. PLAP-1 expression was induced during the course of cytodifferentiation of PDL cells into mineralized-tissue-forming cells in vitro, suggesting the possible involvement of PLAP-1 in the mineralization process of PDL cells. In this study, we hypothesized that PLAP-1 expression is regulated by mineralization-related cytokines in PDL cells. PLAP-1 expression was clearly down-regulated when the cytodifferentiation of PDL cells was reversibly inhibited by fibroblast growth factor-2 (FGF-2). In contrast, bone morphogenetic protein-2 (BMP-2) enhanced PLAP-1 expression. Up-regulation of PLAP-1 expression by BMP-2 was confirmed at the protein level when PDL cells were immunostained with anti-PLAP-1 polyclonal antibody. These results revealed the cytokine-mediated regulatory mechanisms of PLAP-1 expression and suggested that PLAP-1 expression may be associated with the process of cytodifferentiation of PDL cells.