SPOT-008 Neurotensin receptor type 2 protects B-cell chronic lymphocytic leukaemia cells from apoptosis

Introduction B-cell chronic lymphocytic leukaemia (B-CLL) cells are resistant to apoptosis, and consequently accumulate to the detriment of normal B cells and patient immunity. Because current therapies fail to eradicate these apoptosis-resistant cells, it is essential to identify alternative survival pathways as novel targets for anticancer therapies. Material and methods B-cells were isolated from the peripheral blood of healthy donors and CLL patients (n=34) using the MACSxpress human B-CLL Cell Isolation Kit. Gene expression was assessed by RT-qPCR, protein expression and signalling pathway activation was assessed by Western Blot. Protein-protein interaction was confirmed by both Indirect Immuno-Fluorescence and co-immunoprecipitations. Cell death was assessed by Elisa Cell Death as well as Flow Cytometry. Studied receptors were inhibited either by RNA interference or pharmacological inhibitors. Results and discussions In this study, we identified neurotensin receptor 2 (NTSR2) as an essential driver of apoptosis resistance in B-CLL. NTSR2 was highly expressed in B-CLL cells, whereas expression of its natural ligand, neurotensin (NTS), was minimal in both B-CLL cells and patient plasma. Surprisingly, NTSR2 remained in a constitutively active phosphorylated state, caused not by a mutation-induced gain-of-function but rather by an interaction with the oncogenic tyrosine kinase receptor TrkB. Functional and biochemical characterisation revealed that the NTSR2–TrkB interaction acts as a conditional oncogenic driver requiring the TrkB ligand BDNF, which unlike NTS is highly expressed in B-CLL cells. Together, NTSR2, TrkB and BDNF induce autocrine and/or paracrine survival pathways that are independent of mutation status and indolent or progressive disease course. The NTSR2–TrkB interaction activates survival signalling pathways, including the Src and AKT kinase pathways, as well as expression of the anti-apoptotic proteins Bcl-2 and Bcl-xL. When NTSR2 was downregulated, TrkB failed to protect B-CLL cells from a drastic decrease in viability via typical apoptotic cell death. Conclusion Together, our findings demonstrate that the NTSR2–TrkB interaction and the sustained activation of the signalling pathways under the control of these two actors plays a crucial role in B-CLL cell survival, suggesting that inhibition of NTSR2 represents a promising targeted strategy for treating B-CLL malignancy.