CD154 induces a switch in pro‐survival Bcl‐2 family members in chronic lymphocytic leukaemia

Abstract

SummaryChronic lymphocytic leukaemia cells survive and proliferate in patients but rapidly die in culture. The microenvironment that sustains leukaemic cells in vivo contains both stromal cell elements and T cells. We defined changes in Bcl-2 family protein expression on culture with CD40 ligand (CD154) expressed on mouse fibroblast L cells, and interleukin-4 (IL-4; CD154/IL-4 system): conditions that support survival and proliferation. Unexpectedly, Bcl-2 protein expression decreased whilst pro-survival Bcl-x L (as well as A1 and Mcl-1) increased. However, the CD154-L cell/IL-4 system also increased the pro-apoptotic proteins, Bid and Noxa, suggesting that an increased pool of pro-survival factors and not the effects of a single protein mediate survival. Most pro-apoptotic proteins were not induced in drug or spontaneous apoptosis, but expression of Bcl-x S , a pro-apoptotic BCL2L1 isoform, was associated with cell death. This was post-transcriptionally controlled, and, therefore, alternative splicing at the Bcl-x locus appears to have a role in the regulation of chronic lymphocytic leukaemia (CLL) cell survival. This study demonstrated a switch in pro-survival proteins associated with the transition from quiescence to CD154-driven proliferation. CLL therapies targeting Bcl-2 may need to be modified to antagonize proliferation centre-specific prosurvival proteins.

Dichotomy in NF-κB signaling and chemoresistance in immunoglobulin variable heavy-chain-mutated versus unmutated CLL cells upon CD40/TLR9 triggering

“…Although PB CLL cells are prone to apoptosis, sensitive to various drugs and arrested in the G0/G1 phase of the cell cycle, LN CLL cells have an antiapoptotic profile, are supposedly drug resistant and proliferate (Caligaris-Cappio, 2003;Munk and Reed, 2004;Chiorazzi, 2007;Smit et al, 2007). CD40L stimulation of both mutated and unmutated PB CLL cells in vitro results in an antiapoptotic profile with increased expression of Mcl-1, Bcl-X L and Bfl-1 (Willimott et al, 2007), and the development of drug resistance (Smit et al, 2007). However, CD40L stimulation does not induce significant proliferation (Vogler et al, 2008) and thus provides only a partial model for the LN microenvironment.…”

Pro‐survival signal inhibition by CDK inhibitor dinaciclib in Chronic Lymphocytic Leukaemia

“…To mimic this microenvironment in vitro, a number of models have been established, including stimulation with soluble CD154/IL-4, and co-cultures with CD154-expressing fibroblasts together with interleukin-4 (IL-4) (Willimott, et al 2007a). Under these conditions, the expression of anti-apoptotic members of the Bcl-2 family, in particular Bcl-xL and Mcl-1, are greatly increased, which contributes to the resistance to spontaneous-and drug-induced apoptosis in CLL (Vogler, et al 2009, Willimott, et al 2007a, Willimott, et al 2007b.…”

Mcl-1 expression has in vitro and in vivo significance in chronic lymphocytic leukemia and is associated with other poor prognostic markers

“…37 Furthermore, Bcl-2 family proteins, particularly Mcl-1, appear to be dynamically regulated by a wide array of cellular processes, including ligation of the B-cell receptor and signaling via CD40, vascular endothelial growth factor (VEGF), and the PI-3 kinase/ AKT pathway. 35,[40][41][42] Given that the capacity of CLL cells to respond to these signals is strongly linked to a number of important prognostic markers, we set out to evaluate their relationship with Bcl-2 family proteins in a cohort of 185 patients. We also evaluated the association between Bcl-2 family proteins and in vitro responses to fludarabine and assessed the independent prognostic value of these proteins regarding clinical outcome.…”