Modulation of NF-κB Activity and Apoptosis in Chronic Lymphocytic Leukemia B Cells

Abstract

Chronic lymphocytic leukemia (CLL) is an indolent malignancy of CD5+ B lymphocytes. CLL cells express CD40, a key regulator of B cell proliferation, differentiation, and survival. In nonmalignant B cells, CD40 ligation results in nuclear translocation and activation of NF-κB proteins. Based on observations that in some CLL cases, the tumor cells express both CD40 and its ligand, CD154 (CD40 ligand), we proposed a model for CLL pathogenesis due to CD40 ligation within the tumor. To evaluate this issue, we used freshly isolated CLL B cells to examine constitutive and inducible NF-κB activity by electrophoretic mobility shift assay. We consistently observed high levels of nuclear NF-κB-binding activity in unstimulated CLL B cells relative to that detected in nonmalignant human B cells. In each case examined, CD40 ligation further augmented NF-κB activity and prolonged CLL cell survival in vitro. The principle NF-κB proteins in stimulated CLL cells appear to be quite similar to those in nonmalignant human B cells and include p50, p65, and c-Rel. In a CD154-positive case, blocking CD154 engagement by mAb to CD154 resulted in inhibition of NF-κB activity in the CLL cells. The addition of anti-CD154 mAb resulted in accelerated CLL cell death to a similar degree as was observed in cells exposed to dexamethasone. These data indicate that CD40 engagement has a profound influence on NF-κB activity and survival in CLL B cells, and are consistent with a role for CD154-expressing T and B cells in CLL pathogenesis. The data support the development of novel therapies based on blocking the CD154-CD40 interaction in CLL.

Preclinical assessment of curcumin as a potential therapy for B‐CLL

“…As CLL cells constitutively express nuclear NF-kB and basal signaling by this transcription factor appears to play an important antiapoptotic role in these leukemic cells, we next sought to determine whether curcumin treatment of B-CLL cells altered levels of basal nuclear NF-kB. As previously reported, incubation of nuclear extracts of B-CLL cells with a 32 P-labeled oligonucleotide containing a consensus NF-kB-binding sequence revealed constitutive nuclear kB binding activity [11]. The nature of this basal kB-binding activity was further explored through supershift analysis.…”

“…While we do not find consistent evidence that curcumin-induced apoptosis results from PPARg signaling, we did observe that levels of B-CLL cell nuclear NF-kB were reduced by curcumin treatment in the majority of B-CLL samples tested. B-lineage cells, including B-CLL cells, are unusual in that constitutive, low levels of nuclear NF-kB binding activity are present in the absence of exogenous stimuli [11]. Although the explanation for constitutive NF-kB activation in B cells is not clear, it may result from basal signaling from surface immunoglobulin, as B cells rendered deficient in surface immunoglobulin undergo apoptosis [25].…”

“…Given that B-CLL cells, like other B lineage cells, are sensitive to PPARg agonist-induced apoptosis and express constitutive nuclear NF-kB, we wished to determine whether curcumin would induce apoptosis in primary leukemic B-CLL cells in vitro [11]. Our prior studies examining PDE4 inhibitors, a class of drugs that induce apoptosis in B-CLL by a PKA-mediated mechanism, have documented important differences between such primary leukemic cells and lymphoid cell lines, suggesting that a re-examination of curcumin-induced apoptosis in primary malignant lymphoid cells is of some importance [12].…”

Inducible resistance to Fas-mediated apoptosis in B cells

“…The mechanisms utilized by malignant cells may represent perversions of the physiological means by which B cells normally inhibit susceptibility to Fas-mediated apoptosis in a receptor-specific fashion. If true, molecules involved in establishing sIg-induced Fasresistance might form targets for pharmacologic manipulation of the apoptotic balance between host and tumor, including NF-κB, Bcl-xL, FLIP, and/or FAIM [51,56,68,76,154,155].…”

Nuclear factor-κB and inhibitor of κB kinase pathways in oncogenic initiation and progression

“…Consistent with this, NF-kB activation is detected in the bone marrow of patients with myelodysplastic syndrome (Braun et al, 2006), which is considered a precursor disease of AML. NF-kB is also activated in childhood acute lymphoblastic leukemia (Kordes et al, 2000), Hodgkin-Reed-Sternberg cells (Bargou et al, 1997), HTLV-1-positive leukemias (Hiscott et al, 2006), B-cell chronic lymphocytic leukemia (Furman et al, 2000;Zaninoni et al, 2003) and in primary blasts of CML (Kirchner et al, 2003). In addition, NF-kB-dependent gene transcription is a hallmark of the activated B-cell-like subset of diffuse large B-cell leukemia (Lam et al, 2005;Ngo et al, 2006).…”