Tumor Microenvironment Regulates Survival of Mantle Cell Lymphoma Cells through Various Signaling Pathways

Abstract

IntroductionAn 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.MethodsIsolates 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.ResultsCo-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.ConclusionWe 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. DisclosuresRodriguez:Orthobiotech: Research Funding.