The chemical inhibitor of Akt LY294002 pro duced BI 6727 similar results suggesting that ascites mediated Mcl 1 up regulation is not dependent of Akt activation. In contrast, when ERK1 2 activation was inhibited by the specific MEK1 2 inhibitor U0126, ascites mediated upregulation of Mcl 1 protein was sub stantially blocked in both CaOV3 and OVCAR3 cells. Consistent with these results, U0126 signifi cantly blocked the transcriptional upregulation of Mcl 1 by ascites in CaOV3 and OVCAR3 cells. In contrast, the inhibition of Akt by LY294002 had no impact on ascites mediated transcriptional upregulation of Mcl 1 in OC cells. Because Mcl 1 contributes to ascites mediated protection from TRAIL induced apop tosis, we examined whether ERK1 2 has a similar role.

As expected, ERK1 2 inhibition by U0126 significantly blocked ascites mediated protection from TRAIL induced apoptosis. These data demonstrate that ERK1 2 activation upregulates Mcl 1 expression and contributes to ascites mediated attenuation of TRAIL induced apoptosis. Ascites activates Elk 1 transcription Inhibitors,Modulators,Libraries factor via ERK1 2 pathway Previous studies have shown that ERK1 2 can directly Inhibitors,Modulators,Libraries phosphorylate and activate many transcription factors including Elk 1 in breast cancer cells. ERK1 2 acti vation Inhibitors,Modulators,Libraries promotes Elk 1 phosphorylation at Ser383 and its activation. We therefore determine whether ascites treat ment of OC cells resulted in activation of Elk 1. As shown in Figure 4A, the treatment of CaOV3 and OVCAR3 cells with OVC415 ascites resulted in Elk 1 phosphorylation within 30 min and phosphoryl ation declined thereafter.

This was similar Inhibitors,Modulators,Libraries to the kinetic of ERK1 2 that was observed in CaOV3 and OVCAR3 cells. To ensure that ascites Inhibitors,Modulators,Libraries induced Elk 1 phosphorylation was not limited to a single ascites, CaOV3 and OVCAR3 cells were treated with OVC508 and Elk 1 activation was assessed. As shown in Figure 4B, treatment with OVC508 also resulted in Elk 1 activation. Pretreatment with U0126 prevented both ascites induced ERK1 2 and Elk 1 phosphorylation in CaOV3 and OVCAR3 cells. These data dem onstrate that ascites induced Elk 1 activation is ERK1 2 dependent in OC cells. Ascites dependent Elk 1 activation is responsible for Mcl 1 regulation To determine whether ascites induced activation of Elk 1 transcription factor is responsible for Mcl 1 upre gulation, OVCAR3 cells were transfected with Elk 1 or control siRNA and the expression of Elk 1 and Mcl 1 were determined 24 h later by immunoblot.

As shown in Figure 5A, the knockdown of Elk 1 inhibited upregula tion of Mcl 1 by ascites indicating a critical role of Elk 1 in Mcl 1 upregulation. Similar to what we observed in OVCAR3 cells, CaOV3 cells transfected with Elk 1 siRNA displayed reduced Mcl 1 expression at 24 h and 48 h following treatment with OVC415 and OVC439 Erlotinib structure as cites.