Our data suggest TGF- mediated MMP-9 induction may be regulated by the NF-kB, Smad3, and JNK pathways, whereas the IL-1 mediated induction may be regulated by the NF-kB and p38 pathways. be regulated by the NF-kB, Smad3, and JNK pathways, whereas the IL-1 mediated induction may be regulated by the NF-kB and p38 Sntb1 pathways. Inhibition of the p38, NF-kB, or JNK pathways significantly reduced, but did not abrogate, basal MMP-9 levels. Inhibition of the ERK pathway did not have an effect on MMP-9 mediated expression in either the treated or untreated co-transfected cells. expression of many of TFs or adaptor proteins which can aid in the activity of the MMP-9 promoter. TGF- signaling via Smad Smad signaling is the canonical TGF- signaling cascade where binding of TGF- to its receptor induces R-Smad phosphorylation leading to binding by co-Smads and translocation to the nucleus, complexing with other co-activators, DNA binding, and promoter activation. While this pathway is simple enough, the mechanism by which the Smad pathway is usually mediating TGF- induced up-regulation of MMP-9 may be more complex Albaspidin AA as you will find no classical Smad binding elements in the MMP-9 promoter. This does not discount the possibility that the Smad TFs may be binding an unidentified promoter element or that they may be forming a complex and binding the DNA indirectly through another co-activator. For example, Smad3/4 can form a complex with AP-1 and this complex has been shown to be critical for TGF- mediated AP-1 site activation impartial of Smad3 DNA binding[59]. This complex also requires a SIM-containing subunit to bind a CCAG motif downstream of the AP-1 binding element, which the MMP-9 promoter has, further supporting this theory[59]. Alternatively, Albaspidin AA Smad3 has been shown to interact with SP-1 following nuclear translocation in order to induce target genes[60]. Further experiments are needed to Albaspidin AA determine if Albaspidin AA Smad3 is actually bound in a complex to the MMP-9 promoter and if so, in which complex. The Smad pathway may also be acting indirectly to induce MMP-9 by activating the NF-kB pathway as previously mentioned. Or, again like NF-kB, Smad may be inducing gene expression of other effecter TFs. Given all myriad possibilities for cross-talk between signaling pathways only mediating the response to TGF-, and not even considering the possibilities added by IL-1, the complexity of MMP-9 regulation can be staggering. It would be intriguing, however, if there was a simple elegant solution. For example, all pathways mentioned above seem to hinge on JNK activity. It is possible, therefore, that JNK is usually activating both NF-kB and AP-1 as well as Smad3 which can then possibly bind SP-1 or AP-1 along with NF-kB and PEA-3 and enhance promoter activity. This would explain why inhibition of these three pathways can inhibit TGF- mediated MMP-9 expression and why inhibition of only one pathway is insufficient to completely block this expression. Alternatively, these many pathways may be in place as a failsafe, so if one pathway fails, the transmission can be redirected through another pathway. While the efficiency of promoter activation may be lower this could account for the inability of one pathway to completely Albaspidin AA inhibit manifestation. IL-1 signaling via p38 Up to now, we’ve talked about how TGF- may be stimulating MMP-9 from the NF-kB, JNK, and Smad pathways aswell as how IL-1 may be performing via NF-kB. Nevertheless, we’ve also shown how the p38 signaling pathway mediates IL-1 induction of MMP-9. Through the canonical NF-kB pathway triggered by IL-1R activation Apart, this receptor can phosphorylate TRAF6 that may then activate p38 via TAK1[61] also. Unlike inhibiting NF-kB that may stop the signaling pathway at most fundamental level (DNA binding) however, not its upstream focuses on, understanding the system where the p38 pathway mediates the IL-1 excitement of MMP-9 could be.