CITED2-mediated Regulation of MMP-1 and MMP-13 in Human Chondrocytes under Flow Shear

CITED2 (CBP/p300-interacting transactivator with ED-rich tail 2) is a member of the Cited family of nuclear regulators, previously known as mrgl (melanocyte-specific gene-related gene 1). CITED2 is inducible by varying stimuli including lipopolysaccharide, hypoxia, and cytokines such as interleukin 9 and interferon γ. Using the immortalized human chondrocyte cell line, C-28/I2, we investigated whether CITED2 could be responsive to mechanical stimuli, and if so, whether CITED2 could mediate shear-driven regulation of matrix metalloproteinase (MMP) genes. The C-28/I2 cells were cultured under flow shear at 1-20 dyn/cm², and the role of CITED2 in regulation of MMPs was examined using the plasmids encoding sense and antisense CITED2 DNA sequences. The results showed that flow shear at 5 dyn/ cm ² increased CITED2 mRNA and protein levels and down-regulated MMP-1 and MMP-13 mRNA and protein levels as well as enzyme activities. Consistent with the coordinated expression patterns of CITED2 and MMPs, overexpression of CITED2 repressed MMP-1 and MMP-13 mRNA levels and activities, whereas antisense CITED2 plasmids prevented the shear-induced down-regulation of MMP expression. Interleukin-1β induced the formation of p300-Ets-1 complexes without affecting expression of CITED2. Transforming growth factor-β as well as flow shear at 5 dyn/cm² stimulated not only the expression of CITED2 but also the association of CIT-ED2 with p300 by dissociating Ets-1 from p300. These results indicate that CITED2 plays a major role in shear-induced down-regulation of MMP-1 and MMP-13 via a transforming growth factor-β-dependent pathway.