Ultrasound induces cyclooxygenase-2 expression through integrin, integrin-linked kinase, Akt, NF-κB and p300 pathway in human chondrocytes

Abstract

It has been shown that ultrasound (US) stimulation accelerates fracture healing in the animal models and in clinical studies. However, the precise molecular events generated by US in chondrocytes have not been clarified well. Here we found that US stimulation transiently increased the surface expression of α2, α5, β1 or β3 but not α3 or α4 integrins in human chondrocytes, as shown by flow cytometric analysis. US stimulation increased prostaglandin E2 formation as well as the protein and mRNA levels of cyclooxygenase-2 (COX-2). At the mechanistic level, anti-integrin β1 and β3 antibodies or β1 and β3 integrin small interference RNA attenuated the US-induced COX-2 expression. Integrin-linked kinase (ILK) inhibitor (KP-392), Akt inhibitor, NF-κB inhibitor (PDTC) or IκB protease inhibitor (TPCK) also inhibited the potentiating action of US. US stimulation promotes kinase activity of ILK, phosphorylation of Akt. In addition, US stimulation also induces IKKα/β phosphorylation, IκBα phosphorylation, IκBα degradation, p65 phosphorylation at Ser276, p65 and p50 translocation from the cytosol to the nucleus, and κB-luciferase activity. The binding of p65 to the NF-κB element, as well as the recruitment of p300 and the enhancement of p50 acetylation on the COX-2 promoter was enhanced by US. Taken together, our results provide evidence that US stimulation increases COX-2 expression in chondrocytes via the integrin/ILK/Akt/NF-κB and p300 signaling pathway.