SET/PP2A/SHP-1/Lyn oncogenic signaling contributes to tumor aggressiveness in diffuse large B cell lymphoma

Purpose: Diffuse large B-cell lymphoma (DLBCL) is aggressive non-Hodgkin lymphoma. It is a heterogeneous disease and is classified as germinal center B-cell like (GCB) and activated B-cell like (ABC) subtypes according to gene-expression profiling. The oncogenic pathways in DLBCL are potential targets for new therapies. In present study, the role and regulation of SET/PP2A/SHP-1/Lyn axis in DLBCL were investigated. Experimental design: U2932, OCL-Ly3, OCI-Ly7, SU-DHL-6 and DB DLBCL cell lines were used for this study. TD-19, a novel SET/PP2A protein-protein interaction inhibitor, was used to address the molecular events of SET signaling. Cell viability was measured by MTT assay. The apoptotic cells were examined by PI/Annexin V staining and Western blotting. SHP-1, Lyn and pLyn were analyzed by immunohistochemistry on lymphoma tissue microarrays from DLBCL patients. Results: We first examined the effects of two different SET inhibitors, TD-19 that is a SET/PP2A protein protein interaction inhibitor, and FTY720 which is a sphingosine analogue that targets SET, on DLBCL cells. TD-19 and FTY720 significantly decreased cell viability and induced apoptosis. SET inhibition activated PP2A and SHP-1 by reducing pPP2AY307 and pSHP-1S591 and inactivated Lyn by decreasing pLynY396. Overexpression of SET rescued these molecular events, and promoted cell growth and migration. Interestingly, we observed the level of SET was declined by TD-19 and TFY720 treatment. We hypothesized Lyn might up-regulate SET expression. Overexpression of Lyn increased SET level, and was accompanied with phosphorylation of PP2A (pPP2AY307) and SHP-1 (pSHP-1S591). Lyn elevated cell growth and migration and suppressed PP2A and SHP-1 activities. Moreover, exogenous SET restored the FTY720- and TD-19-suppressed pSHP-1 and pLyn. Immunohistochemically, high SHP-1 level was linked to low pLyn level of patient with DLBCL and vice versa. Conclusion: This study established the existence of positive feedback of SET/PP2A/SHP-1/Lyn axis in DLBCL cells, and targeting SET could disrupt this regulation. Citation Format: Ji-Lin Chen, Wen-Chun Tsai, Tien-Yun Lan, Chun-Teng Huang, Pei-Yi Chu, Chia-Han Lee, Ka-Yi Lau, Wan-Lun Wang, Kuen-Feng Chen, Chung-Wai Shiau, Chun-Yu Liu. SET/PP2A/SHP-1/Lyn oncogenic signaling contributes to tumor aggressiveness in diffuse large B cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4372.