Signal transduction pathways involved in the stimulation of tissue type plasminogen activator by interleukin-1alpha and Porphyromonas gingivalis in human osteosarcoma cells

BACKGROUND: Recently, evidences have shown that tissue type plasminogen activator (t-PA) may play an important role in the pathogenesis of periodontal diseases. However, the mechanisms and signal transduction pathways involved in the production of t-PA in human osteosarcoma cells are not fully understood. OBJECTIVES: The purpose of this study was to investigate the caseinolytic activity in human osteosarcoma cell line U2OS cells stimulated with interleukin-1alpha (IL-1alpha) or Porphyromonas gingivalis in the absence or presence of p38 inhibitor SB203580, mitogen-activated protein kinase kinase (MEK) inhibitor U0126, and phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. METHODS: IL-1alpha and the supernatants of P. gingivalis were used to evaluate the caseinolytic activity in U2OS cells by using casein zymography and enzyme-linked immunosorbent assay (ELISA). Furthermore, to search possible signal transduction pathways, SB203580, U0126, and LY294002 were added to test how they modulated the caseinolytic activity. RESULTS: Casein zymography exhibited a caseinolytic band with a molecular weight of approximately 70 kDa, suggestive of the presence of t-PA. Secretion of t-PA was found to be stimulated with IL-1alpha and P. gingivalis during a 2-day culture period (p < 0.05). From the results of casein zymography and ELISA, SB203580, U0126, and LY294002 significantly reduced the IL-1alpha or P. gingivalis-stimulated t-PA production, respectively (p < 0.05). CONCLUSIONS: Our findings demonstrated that IL-1alpha and P. gingivalis enhance t-PA production in human osteosarcoma cells, and that the signal transduction pathways p38, MEK, and PI3K are involved in the inhibition of t-PA. SB203580, U0126, and LY294002 suppress t-PA production and/or activity and may therefore be valuable therapeutics in t-PA-mediated periodontal destruction, and might be proved clinically useful agents, in combination with standard treatment modalities, in the treatment of periodontitis.