WL, JLX, WJL, ZWH, YPH, LH, YWS, QW, YW and YYC obtained the data. MDR, MCL1, Survivin in YAP-overexpressing cells. Thus, we proposed a novel mechanism in which YAP augments COX-2 expression as well as its downstream targets, Survivin, MDR, MCL1, and thereby up-regulates the effect of drug resistance in CRC cells. Recently, with the identification of more regulatory components, the Hippo pathway seems to be far from a simple linear pathway. Its activity is clearly mediated through crosstalk with other signaling pathways. The WNT, transforming growth factor- (TGF)Cbone morphogenetic protein (BMP), Hedgehog (HH), Notch, insulin and mTOR pathways have all been reported to functionally interact with the Hippo pathway [29]. Although both COX-2 and YAP play important role in cell proliferation, survival and tumor maintenance, whether there is cross-talk between them remains poorly understood. In the present study, we found that YAP and COX-2 were both overexpressed in CRC cells. YAP up-regulated COX-2 protein expression at the level of transcription. Deletion of the TEAD binding site in the COX-2 promoter diminished COX-2 transcriptional induction by YAP indicating that an intact TEAD binding site was necessary for YAPs induction of COX-2. Also, YAP up-regulated COX-2 catalyzed product, PGE2, and downstream targets MDR, MCL1 and Survivin. These findings clearly indicate that Hippo-YAP signaling mediates the functions of COX-2/PGE2/EPs pathway and YAP is a nexus of the two pathways. Having shown that there was an interaction between Hippo-YAP and COX-2 pathway and COX-2-mediated chemoresistance was regulated by YAP signaling, was there a possibility that COX-2 regulated YAP expression vice versa? Our preliminary study showed that in COX-2-overexpressing HepG2 cells, COX-2 knockdown reduced the expression of YAP. In addition, by overexpressing COX-2 in COX-2-low immortal THLE-3 hepatic cells, enhanced levels of COX-2 were accompanied by up-regulation of YAP expression (data not shown). These results suggested that a feedback loop may exist between YAP and COX-2. Hydrogen sulfide-releasing non-steroidal anti-inflammatory drugs (HS-NSAIDs) are a new class of compounds with potential in alleviating gastrointestinal and cardiovascular adverse effects [30]. Some of them are now in clinical trial II. Recently, some of HS-NSAIDs have been shown with potency in inhibiting the growth of human cancers. However, studies regarding the underlying mechanism have not been abundantly carried out. In this study, we found that G-4 could drive YAP from DNA31 nucleus to cytosol and promote its retention in cytosol through phosphorylation, hence affecting the downstream events such as YAP transcription. This mechanism has become one of the therapeutic DNA31 targets for agents that have been found to disturb the Hippo pathway (Fig.?13). DNA31 Additionally, as expected, G-4 showed direct COX-2 inhibition independent of its suppression on YAP. As a result, G-4 can be identified as a dual inhibitor of YAP and COX-2. Because YAP and COX-2 are involved in drug resistance, we further discovered that their downstream effectors such as CTGF, Cyr 61, MCL, MDR1, Survivin, Bcl-xL were down-regulated and G-4 demonstrated remarkable effect on biological behaviors of Taxol resistant cells (Fig.?14). Finally, we turned to whether YAP and COX-2 had synergistic performance in keeping resistance. Results showed that not only G-4 was more potent than VP or celecoxib (a single inhibitor of YAP or COX-2) in inducing apoptosis and reducing viability of Taxol resistant CRC cells, but also combination of shYAP and COX-2 exhibited advantages over either shYAP or shCOX-2 alone. These results point to the idea that targeting YAP and COX-2 would be more efficacious than single inhibition in overcoming drug resistance regarding YAP/COX-2 high expression and G-4 could be a novel drug candidate for successful drug resistant CRC treatment. Open in a separate window Fig. 13 Agents that affect the Hippo pathway?(Nat Rev Cancer. 2015;15(2):73-79.)?????? Open in Rabbit Polyclonal to Smad1 a separate window Fig. 14 YAP mediates drug-resistance through triggering COX-2 over-expression and regulatory effects of G-4 Conclusions In conclusion, this study demonstrates that YAP is an upstream regulator of COX-2 and targeting YAP-COX-2 may be a potential promising strategy to treat drug-resistant colorectal cancers. G-4 may provide a promising alternative therapeutic approach for cancer patients DNA31 who are not sensitive to YAP or COX-2 inhibitor. Dual inhibitors of YAP and COX-2 may be of particular value for chemotherapeutic drug resistance in tumors with high levels of YAP/COX-2 expression. Additional files.
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