| The degradation of extracellular matrix by proteases is an essential process during tissue repair, in remodeling, and in pathologic processes such as inflammation and neoplastic growth. Urokinase-type plasminogen activator (uPA) is a very important serine protease, which is best known for its role in the initiation of the pericellular proteolystic cascade. uPA is secreted as a single-chain protein (scuPA or pro-uPA) from various cells including fibroblast. Secreted pro-uPA binds to urokinase-type plasminogen activator receptor (uPAR) and is subsequently activated to the active two-chain form uPA (tcuPA). Active uPA then converts plasminogen into plasmin, a trypsin-like serineprotease, that is not only responsible for the degradation of fibrin, but also contribute directly or indirectly, via initiating the activation of metalloproteases (MMP), to the degradation and turnover of the extracellular matrix.Periodontal diseases are inflammatory diseases, characterized by bacterial infections that cause gingival inflammation and tissue destruction, ultimately leading to resorption of periodontal bone. Recently, the uPA-plasmin proteolytic system has received considerable attention because of its participation in degrading periodontal extracellular matrix in periodontal diseases. Substantial studies have demonstrated that uPA-plasmin system is involved in the progression of periodontal diseases. LPS is a cell wall constituent of gram-negative bacterium, which is generally believed to be a key factor in the development and progression of periodontal diseases. LPS can modulate cell growth, synthetic activity, and bone metabolism, as well as stimulate the macrophages. monocxles, and fibroblasts to secrets such inflammatory molecules as interlukin 1 (IL-1). tumor necrosis factor a (TNF-a) and prostaglandins (PGE). Recent studies suggest that LPS stimulates the activity of uPA-plasmin system in periodontal tissue. LPS stimulates the plasmin activity and uPA activity in both the conditioned medium and cell lysates of gingival fibroblasts. Furthermore. LPS increases the protein and mRNA level of uPA in gingival fibroblasts. But the mechanism of LPS-induced uPA expression in gingival fibroblasts is still unknown.The aim of the present study is to clarify the signal transduction pathway of LPS-induced uPA expression in fibroblasts. Human gingival fibroblasts and embryonal kidney 293 cells were used in this study. Firstly, we tested the effect of LPS on uPA expression in human gingival fibroblasts. We demonstrated that LPS induced uPA expression in gingival fibroblasts. p38 MAPK signal pathway plays important roles in inflammation, cell growth, cell differentiation, the cell cycle, and cell death, and it could be rapidly phosphorylated by LPS stimulation. Recently. p38 MAPK signaling pathway has been shown to beimportant for the induction of several proteases by extracellular stimuli. In this study, we demonstrated that LPS could activate p38 MAPK in gingival fibroblasts. Take together. LPS can induce p38 MAPK activity and uPA expression, meanwhile p38 MAPK signal pathway plays an important role in proteases expression. These findings prompted us to investigate whether p38 MAPK signal pathway is involved in LPS-induced uPA expression in human gingival fibroblast. We found that p38-specific inhibitor SB203580 significantly inhibited the LPS-induced mRNA and protein levels of uPA in gingival fibroblasts. These results suggest that activity of p38 MAPK is essential for LPS-induced uPA expression in human sinaival fibroblasts.The expression of uPA mRNA may be regulated b) LPS at either the transcriptional or mRNA stability levels or both. In this study, we found that LPS has no effect on uPA promoter activity in human gingival fibroblasts. In contrast, when we measured the stability of uPA mRNA. we found that LPS increased half-life of uPA mRNA to over 12 h in gingival fibroblasts. Interestedly, the induction of LPS on mRNA stability of uPA was inhibited strongly by treatment of SB203580. In cells treated with SB203...
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