MMPs synthe sis by altering SOCS1 e pression levels in the SW1353 chondrosarcoma cells. When nontransfected SW1353 cells were stimulated with IL 1B, MMP 1, MMP 3, and MMP 13 secretion were significantly increased, consistent with previous reports. In con trast, the SOCS1 overe pressing chondrocytes produced significantly lower levels of MMPs on addition of IL 1B. Conversely, levels of MMP 1, MMP 3, and MMP 13 were significantly increased in the SOCS1 knockdown SW1353 cell line that was transfected with lentiviral SOCS1 shRNA. The secretion of TIMP 1 from SOCS1 overe pressing or knockdown cell lines was not altered under all of these conditions. Also, ADAMTS 4 mRNA e pression was suppressed in the SOCS1 overe pressing SW1353 cells and increased in the SOCS1 knockdown SW1353 cells.
These data suggest that SOCS1 effect ively modulates the catabolic response of chondrocytes to Entinostat IL 1B. To verify the inhibitory effects of SOCS1 in primary HACs, we investigated the changes in MMPs and ADAMTS 4 e pression after IL 1B stimulation in HACs that were transiently electrotransfected with pShuttle2 SOCS1 vectors. SOCS1 was increased at least by 19 fold compared with empty vector transfected HACs. The IL 1B induced MMPs and ADAMTS 4 mRNA e pression levels were significantly downregulated in SOCS1 overe pressing HACs, similar to the SOCS1 overe pressing SW1353 cells. Effects of SOCS1 on MAPK and NF ��B signaling pathway IL 1B signaling involves activation of both MAPK and NF ��B pathways. Indeed, SOCS1 overe pression de creased the phosphorylation level of p38 and JNK after IL 1B stimulation, whereas SOCS1 knockdown increased their phosphorylation.
as reflected by the low luciferase activity. These data suggest that SOCS1 inhibits NF ��B activity via preventing I��B from degradation. To ascertain the contributions of MAP kinase and NF ��B pathways to each MMP production, the SOCS1 knockdown chondrocytes were pretreated with various kinase inhibitors 1 hour before IL 1B stimulation. The p38 inhibitor SB202190 significantly suppressed the produc tion of MMPs, even at a lower dose. JNK and ERK inhibitors also inhibited MMPs secretion in a dose dependent manner. Although the After IL 1B stimulation, the phosphorylation levels of NF ��B p65 did not change at the serine 311 or 536 sites in the SOCS1 overe pressing cells, although the levels of phospho NF ��B p65 were increased in the SOCS1 knockdown cells.
As NF ��B activity is controlled by the inhibitor protein I��B, we inves tigated the change in the amount of I��B. The SOCS1 overe pression prevented the I��B degradation, whereas the SOCS1 knockdown could not. Accordingly, the NF ��B dependent gene e pression was significantly decreased in the SOCS1 overe pressing chondrocytes, effect of SN50 was less dramatic than that of MAP kinase inhibitors, blocking of NF ��B translocation re duced MMP 1 and MMP 13 production. Effects of SOCS1 on TAK1 kinase TAK1 is a MAPK kinase kinase family protein that is ac tivated by several cytokines,