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Fibroblast growth factor-1 Inhibition Enhances FAS-Induced Apoptosis in Mantle Cell Lymphoma Cells by Accelerated BIRC2/3 Degradation. Neeraj Jain1, Tamer Khashab1, Natalie Willingham2, Felipe Samaniego1 and Lalit Sehgal2 1 Department of Lymphoma/Myeloma, UT MD Anderson Cancer center, Houston, TX 77054 2 Division of Hematology, Comprehensive Cancer Center, The Ohio State University, Columbus, OH, USA Introduction Mantle cell lymphoma (MCL) is an aggressive form of non-Hodgkin lymphoma that is characterized by the t(11:14)(q13:p32) translocation. MCL cells have altered cyclinD1 levels, impaired cell cycle regulation, DNA damage response, and likely defects in apoptosis signaling. Furthermore, up-regulated anti-apoptotic mediators such as the target of NF-κB BIRC2 and BIRC3 were correlated with decreased apoptosis signaling. Also many cancer cells and malignant tumors show a prevalent resistance to apoptosis induction by FAS. Thus, by understanding the underpinnings of apoptosis resistance, we will be in a better position to develop strategies that improve Fas-induced killing of lymphoma cells. Methods More detailed insight into MCL pathogenesis has been delayed until the recent development of a tissue culture system, using human mesenchymal stromal cells (hMSC), suitable for propagating primary MCL cells. Isolates of primary MCL cells were co-cultured with human mesenchymal stem cells (hMSCs) and the content of MCL-ICs was analyzed by flow-cytometry based on marker expression profile; CD34-CD3-CD45+CD19-. Cytokine array was used to identify the soluble factors enriched in the co-cultures and the expression of these factors was confirmed by RT-PCR analysis. The signaling pathways employed by the newly-identified factors were blocked in 3 MCL cell lines (JVM2, Mino, Z138) to confirm their essential role in survival of MCL cells and, more importantly, for MCL-ICs. Results Co-cultures of primary MCL isolates with hMSCs supported the growth of MCL cells for over 4 weeks with continued presence of MCL-ICs (CD34-CD3-CD45+CD19-) representing about 1% of MCL cells. We found that IL-6 produced by hMSCs triggered an FGF/FGFR autocrine loop in MCL-ICs. The extent of FGFR expression correlated tightly with expression of SOX11, a pathology related negative prognostic marker in MCL. MCL cell survival and growth was regulated via the FGFR-1 mediated BIRC2/3 axis. Blocking of this signaling pathway with FGFR-1 inhibitors consistently induced early degradation in BIRC2/3 levels and subsequently MCL cell death. Conclusion We established that propagation of primary MCL in co-cultures with hMSCs depends on activation of FGF/FGFR-1 autocrine loop that enhances BIRC2/3 protein expression and thus, supports survival of MCL cells. We identified the factors essential for survival of MCL and MCL-ICs that present new targets for improved MCL treatment strategies. This study reveals that inhibition of FGFR-1 signaling by specific inhibitor has a profound positive impact on extrinsic cell death signaling; it enhances FAS sensitivity by promoting processing of caspases through enhanced BIRC2/3 degradation. The capacity of FGFR-1 inhibition to target stability of BIRC2/3, underscores its potential for enhancing efficacy of conventional cancer therapies. Disclosures Samaniego: ADC Therapeutics: Research Funding.

Additional file 5: Figure S4. MALAT1 knockdown enhances MCL cell apoptosis in vitro. In flow cytometric analysis of annexin V/PI staining, the percentage of either early or late apoptotic cells increases in MALAT1 knock down cells.

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Introduction An aggressive, incurable form of non-Hodgkin's lymphoma (NHL) is classifed as Mantle cell lymphoma (MCL). The health complications associated with advanced age of restrict treatment with intense chemotherapy. Overexpression of cyclin-D1 due to Translocation t(11;14) , is the hallmark of MCL. More detailed insight into MCL pathogenesis has been delayed until the recent development of a tissue culture system, using human mesenchymal stromal cells (hMSC), suitable for propagating primary MCL cells. We hypothesized that tumor-initiating cells are responsible for MCL relapse and chemoresistance and thus, identification of signals responsible for survival and maintenance of MCL-initiating cells (MCL-ICs) is essential for design of curative treatment strategies. Methods Isolates of primary MCL cells (n=24) were co-cultured with human mesenchymal stem cells (hMSCs) and the content of MCL-ICs was analyzed by flow-cytometry based on marker expression profile; CD34-CD3-CD45+CD19-. Cytokine array was used to identify the soluble factors enriched in the co-cultures and the expression of these factors was confirmed by RT-PCR analysis. The signaling pathways employed by the newly-identified factors were blocked in 3 MCL cell lines (JVM2, Mino, Z138) to confirm their essential role in survival of MCL cells and, more importantly, for MCL-ICs. Results Co-cultures of primary MCL isolates with hMSCs supported the growth of MCL cells for over 4 weeks with continued presence of MCL-ICs (CD34-CD3-CD45+CD19-) representing about 1% of MCL cells. We found that IL-6 produced by hMSCs triggered an FGF/FGFR autocrine loop in MCL-ICs. The extent of FGFR expression correlated tightly with expression of SOX11, a pathology related negative prognostic marker in MCL. MCL cell survival and growth was regulated via the FGFR/mir101/ EZH2/ NF-κB/XIAP axis. Blocking of this signaling pathway with FGFR1 inhibitors consistently induced early reduction in XIAP levels and subsequently MCL cell death. Conclusion We established that propagation of primary MCL in co-cultures with hMSCs depends on an FGF/FGFR autocrine loop that enhances XIAP protein expression and thus, supports survival of MCL cells. We identified the factors essential for survival of MCL and MCL-ICs that present new targets for improved MCL treatment strategies. Disclosures Rodriguez: Orthobiotech: Research Funding.

Additional file 7: Figure S6. Knockdown of MALAT1 and cell cycle profile. Cell cycle analysis of control (si-NC) and MALAT1 knockdown cells (si-MALAT1) post-mitotic release. a Transfected MCL cells (Mino and Jeko-1) were treated with nocodazole for 24 hours for synchronization and examined for G1/S progression 18 hours after released. b Cell cycle analysis of control and MALAT1 knockdown cells by flow cytometry.

Additional file 7: Figure S6. Knockdown of MALAT1 and cell cycle profile. Cell cycle analysis of control (si-NC) and MALAT1 knockdown cells (si-MALAT1) post-mitotic release. a Transfected MCL cells (Mino and Jeko-1) were treated with nocodazole for 24 hours for synchronization and examined for G1/S progression 18 hours after released. b Cell cycle analysis of control and MALAT1 knockdown cells by flow cytometry.