The novel Akt inhibitor API-1 induces c-FLIP degradation and synergizes with TRAIL to augment apoptosis independent of Akt inhibition

• Type of Material: Article
• Authors: Bo Li, Emory University; Hui Ren, Emory University; Ping Yue, Emory University; Mingwei Chen, Xi’an Jiaotong University; Fadlo Khuri, Emory University; Shi-Yong Sun, Emory University
• Language: English
• Date: 2012-04
• Publisher: American Association for Cancer Research
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: ©2012 American Association for Cancer Research.
• Final Published Version (URL): http://cancerpreventionresearch.aacrjournals.org/content/5/4/612
• Title of Journal or Parent Work: Cancer Prevention Research
• ISSN: 1940-6207
• Volume: 5
• Issue: 4
• Start Page: 612
• End Page: 620
• Grant/Funding Information: Georgia Cancer Coalition Distinguished Cancer Scholar award (to S-Y. S.) and National Cancer Institute NIH SPORE P50 grant CA128613 (project 2 to S-Y. S and F. R. K).
• Keywords: TRAIL; API-1; apoptosis; cancer; c-FLIP; Akt
• Research Categories: Health Sciences, Oncology

Abstract

API-1 is a novel small molecule inhibitor of Akt, which acts by binding to Akt and preventing its membrane translocation, and has promising preclinical antitumor activity. In this study, we reveal a novel function of API-1 in regulation of c-FLIP levels and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, independent of Akt inhibition. API-1 effectively induced apoptosis in tested cancer cell lines including activation of caspase-8 and caspase-9. It reduced the levels of c-FLIP without increasing the expression of DR4 or DR5. Accordingly, it synergized with TRAIL to induce apoptosis. Enforced expression of ectopic c-FLIP did not attenuate API-1-induced apoptosis, but inhibited its ability to enhance TRAIL-induced apoptosis. These data indicate that downregulation of c-FLIP mediates enhancement of TRAIL-induced apoptosis by API-1, but is not sufficient for API-1-induced apoptosis. API-1-induced reduction of c-FLIP could be blocked by the proteasome inhibitor MG132. Moreover, API-1 increased c-FLIP ubiquitination and decreased c-FLIP stability. These data together suggest that API-1 downregulates c-FLIP by facilitating its ubiquitination and proteasome-mediated degradation. Since other Akt inhibitors including API-2 and MK2206 had minimal effects on reducing c-FLIP and enhancement of TRAIL-induced apoptosis, it is likely that API-1 reduces c-FLIP and enhances TRAIL-induced apoptosis independent of its Akt-inhibitory activity.