7D). To address how YAP works on BTRC expression, BTRC was examined in HepG2 cells with either YAP knocked down or ectopically expressed. We found that BTRC was up-regulated by knockdown of YAP (Fig. 7E), whereas it was down-regulated by overexpression of YAP (Fig. 7F). On the basis of the interaction between YAP and CREB, we investigated the growth of HepG2 clones after injection into athymic mice. Compared to the control, HepG2 cells with either YAP or CREB knocked down effectively prevented tumor growth, but such effects could be rescued by simultaneously Idelalisib supplier overexpressing either CREB or YAP in a nude mouse model (Fig. 8A).

Thus, we confirmed such a close relationship in vivo. Although much is known about its posttranslational modification, the transcriptional regulation of YAP, as well as the cross-talk between YAP and other pathways, is still poorly understood. In the present study, we show that YAP-CREB interaction is critical for liver cancer cells, both in vitro and in vivo, through a positive autoregulatory feedback loop. We revealed that YAP inhibited the degradation of CREB mediated by BTRC and p38, and the accumulation of CREB, in turn, stimulated YAP transcription. Moreover, both CREB and YAP proteins are highly expressed in a subset of human liver cancer samples and are closely correlated, suggesting an important role of this feedback loop in liver cancers. Without a DNA-binding domain, YAP

has to work through target transcription factors, such as TEAD family proteins Runx2, Smads, and so on.[16] Selleckchem Ganetespib Because of

the fact that there were no co-occupancies of YAP and CREB at CRE of YAP, Rab25, and HULC promoters by ChIP assay (data not shown), we believe that YAP proteins do not act as cotranscription factors to CREB, but rather as regulators to CREB activity (Fig. 3). In a recent study, Skouloudaki and Walz[19] reported that YAP recruits tyrosine kinase c-Abl, antagonizes the function of Nedd4.2, an E3 ubiquitin-ligase, and thus protects AMOTL1 from degradation. Similarly, our findings reveal a new role of YAP in protecting another protein CREB from degradation. Phosphorylation on CREB ser133 by MAPK14/p38 kinase primes subsequent CREB degradation (Fig. 5 and Supporting Fig. 5), which can be blocked by YAP (Fig. 6). YAP controls phosphorylation Aprepitant of MAPK14/p38 through BTRC (Fig. 7), an E3 ligase that interacts with and mediates YAP unbiquitination and degradation.[18] Conversely, we first uncovered that this interaction also facilitates BTRC degradation (Fig. 7). Noubissi et al.[20] reported that β-catenin stabilizes BTRC mRNA by enhancing an RNA-binding protein CRD-BP, expression through promoter binding and, ultimately, elevates BTRC protein levels. Also, Imajo et al.[21] demonstrated that YAP suppresses the nuclear translocation of β-catenin by directly binding to it in the cytoplasm, thereby inhibiting β-catenin.