Fatty acid synthase (FASN) and protein translational machinery are two emerging cancer therapeutic targets, but their mutual dependency on each other for tumor growth especially in diffuse B-cell large lymphoma (DLBCL) is currently unknown. Therefore, we investigated the functional consequences of enhanced FASN activity on protein translational machinery in both DLCBL cell lines as well as primary samples. Inhibition of FASN activity by a specific inhibitor, C75 or shRNA mediated knockdown, suppressed de novo protein synthesis in SUDHL2, Pfeiffer, and HLY-1 cells, whereas SUDHL4 and SUDHL6 cells displayed minimal impact. Assessing the core translational machinery, the eif4b (eukaryotic initiation factor 4b) levels were depleted in a dose dependent manner of C75 treatment or shRNA mediated knock down of FASN. Mechanistically, eif4b undergoes ubiquitin mediated protein degradation upon FASN depletion. Importantly there seems to be a direct correlation between FASN levels and eif4b expression in DLBCL samples. Depleting the expression of eif4b significantly reduced the cell proliferative capacity of both FASN sensitive as well as resistant DLBCL cells. Screening the interacting protein partners from the available databases, we observed that USP11 interacts and deubiquitinates eif4b which increases its overall stability. Furthermore altering the expression of USP11 or its activity by either chemical inhibition or mutations significantly alters nascent peptide synthesis. Significantly, either down regulating USP11 or inhibiting via small molecules significantly reduced the cell proliferation with increased apoptosis of either FASN activity sensitive or resistant DLBCL cells. USP11 expression was also elevated in DLBCL tissues. Importantly, there is a strong correlation between USP11 and FASN as well as eif4b expression in DLBCL with higher level of this proteins associated with poorer survival. Enhanced FASN activity increased the Akt kinase activity, which phosphorylates USP11 at an evolutionary conserved site. FASN stimulated Akt-meditated phosphorylation events is critical for USP11 recruitment on translational initiation machinery as well as interaction with eif4b to alter protein biosynthesis. These results demonstrate that FASN mediated eif4b/USP11 axis is required for cell proliferation and survival by regulating the translation of proliferative and prosurvival mRNAs. Targeting the eif4b/USP11 axis for therapeutic intervention may add additional treatment options for resistant/relapsed DLBCL patients.
Citation Format: Bandish Kapadia, Ronald Gartenhaus. Understanding the functional role of enhanced FASN activity in regulating protein translation in DLCBL. [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr A33.