Endogenous Neurotrophins and Trk Signaling in Diffuse Large B Cell Lymphoma Cell Lines Are Involved in Sensitivity to Rituximab-Induced Apoptosis

Abstract

BackgroundDiffuse large B-cell lymphoma (DLBCL) is a common and often fatal malignancy. Immunochemotherapy, a combination of rituximab to standard chemotherapy, has resulted in improved survival. However a substantial proportion of patients still fail to reach sustained remission. We have previously demonstrated that autocrine brain-derived neurotrophic factor (BDNF) production plays a function in human B cell survival, at least partly via sortilin expression. As neurotrophin receptor (Trks) signaling involved activation of survival pathways that are inhibited by rituximab, we speculated that neurotrophins may provide additional support for tumour cell survival and therapeutic resistance in DLBCL.Methodology/Principal FindingsIn the present study, we used two DLBCL cell lines, SUDHL4 and SUDHL6, known to be respectively less and more sensitive to rituximab. We found by RT-PCR, western blotting, cytometry and confocal microscopy that both cell lines expressed, in normal culture conditions, BDNF and to a lesser extent NGF, as well as truncated TrkB and p75NTR/sortilin death neurotrophin receptors. Furthermore, BDNF secretion was detected in cell supernatants. NGF and BDNF production and Trk receptor expression, including TrkA, are regulated by apoptotic conditions (serum deprivation or rituximab exposure). Indeed, we show for the first time that rituximab exposure of DLBCL cell lines induces NGF secretion and that differences in rituximab sensitivity are associated with differential expression patterns of neurotrophins and their receptors (TrkA). Finally, these cells are sensitive to the Trk-inhibitor, K252a, as shown by the induction of apoptosis. Furthermore, K252a exhibits additive cytotoxic effects with rituximab.Conclusions/SignificanceCollectively, these data strongly suggest that a neurotrophin axis, such NGF/TrkA pathway, may contribute to malignant cell survival and rituximab resistance in DLBCL.

Neurotrophins and B-cell malignancies

“…This may allow them to better survive the tumour microenvironment, such as the lymph nodes, or to increase resistance to therapy. In response to the therapeutically relevant anti-CD20 monoclonal antibody rituximab, the cell lines increased expression and secretion of NGF, presumably leading to NGF-p75 NTR pro-survival signaling, as TrkA was not observed [126].…”

“…This suggests that these cells may have some basal BDNFTrkB 95 signaling. Constitutive PI3K/Akt signaling was also observed in SUDHL cells [126], however, the involvement of BDNF/TrkB in this would need to be confirmed by inhibiting BDNF signalling. TrkA was largely not expressed, consistent with a lack of NGF secretion [126].…”

“…and SUDHL6 DLBCL cell lines have been shown to express proNGF and proBDNF intracellularly, while secreting only low levels of pro-and mature BDNF and not NGF in normal culture conditions [126]. OCI-LY3…”

“…These cells also express p75 NTR , TrkB 95 and sortilin (SUDHL4/6 cells; [126]; TrkA, TrkB 95 and TrkC (OCI-LY19); or TrkB 95 and TrkC (OCI-LY3; [127]).…”

TrkA is a binding partner of NPM‐ALK that promotes the survival of ALK+ T‐cell lymphoma

“…Furthermore, deregulation of NGF/TrkA signaling has been shown to be involved in the pathogenesis and survival of non‐neural malignancies including prostate, pancreas, skin, breast, and liver cancers (Lagadec et al ., 2009; Miknyoczki et al ., 2002; Oelmann et al ., 1995; Rasi et al ., 2007; Shonukan et al ., 2003). Notably, fewer studies have explored the role of NGF/TrkA signaling in hematological malignancies including NPM‐ALK + T‐cell lymphoma (Bellanger et al ., 2011; Kim et al ., 2013; Rao et al ., 2010). …”