CD180 functions in activation, survival and cycling of B chronic lymphocytic leukaemia cells

We previously showed that approximately 60% of B chronic lymphocytic leukaemia (B-CLL) cells express surface CD180, an orphan receptor of the Toll-like receptor family. Here we investigated the ability of anti-CD180 monoclonal antibody (mAb) to induce activation, cell cycling, survival and signalling in B-CLL cells and normal B cells. Upon addition of anti-CD180 mAb, alone or in combination with anti-CD40 mAb or recombinant IL-4 (rIL-4), expression of CD86, Ki-67, uptake of DiOC(6) , phosphorylation of signalling protein kinases and Ca(2+) flux were measured in B-CLL cells from untreated patients and normal B cells from age-matched volunteers. Normal B cells and approximately 50% of CD180(+) B-CLL clones responded to CD180 ligation by activation, cycling and increased survival comparable with, or superior to, those induced by anti-CD40 mAb or rIL-4 (Responder B-CLL). Non-responder CD180(+) B-CLL clones failed to respond to CD180 mAb and responded poorly to CD40 mAb and rIL-4. Anti-CD180 mAb induced phosphorylation of ZAP70/Syk, Erk, p38MAPK and Akt in normal B cells and Responder B-CLL cells. In contrast, Erk, p38MAPK and Akt were not phosphorylated in Non-responder B-CLL cells indicating a block in signalling and possible anergy. CD180 may provide powerful expansion and survival signals for Responder B-CLL cells and have an important prognostic value

Rewiring of sIgM-mediated intracellular signaling through theCD180 Toll-like receptor

Chronic Lymphocytic Leukaemia (CLL) development and progression is thought to be driven by unknown antigens/autoantigens through the B cell receptor (BCR), and environmental signals for survival and expansion including Toll-like receptor (TLR) ligands. CD180/RP105, a membrane-associated orphan receptor of the TLR family, induces normal B cell activation and proliferation and is expressed by approximately 60% of CLL samples. Half of these respond to ligation with anti-CD180 antibody by increased activation/phosphorylation of protein kinases associated with BCR signaling. Hence CLL cells expressing both CD180 and the BCR could receive signals via both receptors. Here we investigated cross-talk between BCR and CD180-mediated signaling on CLL cell survival and apoptosis. Our data indicate that ligation of CD180 on responsive CLL cells leads to activation of either pro-survival BTK/PI3K/AKT-mediated, or pro-apoptotic p38MAPK-mediated signaling pathways, whilst sIgM ligation predominantly engages the BTK/PI3K/AKT pathway. Furthermore, pre-treatment of CLL cells with anti-CD180 redirects IgM-mediated signaling from the pro-survival BTK/PI3K/AKT towards the pro-apoptotic p38MAPK pathway. Thus pre-engaging CD180 could prevent further pro-survival signaling mediated via the BCR and, instead, induce CLL cell apoptosis, opening the door to therapeutic profiling and new strategies for the treatment of a substantial cohort of CLL patients