c-Abl regulates Mcl-1 gene expression in chronic lymphocytic leukemia cells

Abstract

IntroductionChronic lymphocytic leukemia (CLL) is a malignant disease characterized by the gradual accumulation of mature, nonproliferative B cells expressing a distinctive group of surface markers, including CD19, CD23, and CD5. 1,2 It is a heterogeneous disease that can follow an indolent or aggressive course, and understanding the nature of this heterogeneity is an area of intense research interest. 2 CLL cells are resistant to apoptosis, and this is thought to be regulated by survival signals from the microenvironment coupled with intrinsic defects in apoptotic machinery. [3][4][5][6][7] Therefore, understanding in greater detail the molecular basis of such apoptotic resistance may help lead to the discovery of agents effective in CLL treatment.The more aggressive, poor prognostic course of CLL positively correlates with a series of cellular markers, such as ZAP70, CD38, and unmutated IgV H . [8][9][10] Recently, it has been reported that high expression levels of the antiapoptotic protein Mcl-1 in CLL cells correlate with both poor disease prognosis 11 and in vitro and in vivo chemoresistance. [11][12][13][14] Moreover, down-regulation of Mcl-1 using antisense oligonucleotides results in cell death during in vitro culture, 15 and elevated Mcl-1 protein expression has been shown to prolong the survival of CLL cells exposed to a variety of apoptosis-inducing stimuli. 16 Taken together, this evidence establishes Mcl-1 as a critical mediator of CLL cell survival.Another signaling protein overexpressed in CLL cells that plays a role in apoptotic resistance is the nonreceptor tyrosine kinase c-Abl. 17 c-Abl appears to be important for normal B-cell development because targeted disruption of the gene encoding this protein in mice results in development of lymphopenia. 18 c-Abl functions in B cells to phosphorylate CD19 after antigen engagement of the B-cell receptor (BCR), highlighting c-Abl as an important regulator of B-cell signaling. 19 In CLL, the overexpression of c-Abl stimulates activity of the nuclear factor-B (NF-B) pathway, leading to increased resistance of the malignant cells to spontaneous apoptosis. 17 Thus, a pathophysiologic role for this kinase in CLL is in the regulation of prosurvival signaling.Active NF-B is known to induce the autocrine expression of cytokines, such as interleukin-6 (IL-6). 20 IL-6 in CLL is associated with adverse disease features and reduced patient survival. 4 It is thought that elevated levels of IL-6 can promote disease progression either indirectly through effects on the microenvironment or directly through effects on cell survival and proliferation. An example of the direct effect of IL-6 is its capability of activating the transcription factor STAT3 via the classic IL-6 receptor (IL-6R) pathway. 21 Such stimulation of STAT3 then promotes up-regulation of antiapoptotic genes, such as Mcl-1. [22][23][24] A role for c-Abl in the activation of STAT3 has been described, 25 as well as a connection, in chronic myelogeneous leukemia (CML) cells, between c-Abl and Mcl-1. 21 Th...

LCK Is an Important Mediator of B-Cell Receptor Signaling in Chronic Lymphocytic Leukemia Cells

“…Nucleofections were carried out according to established protocol (31). Briefly, 1 Â 10 7 CLL cells were transfected using the Amaxa solution V transfection kit according to the manufacturer's instructions (Lonza Biologics plc).…”

The Aurora A and B kinases are up-regulated in bone marrow-derived chronic lymphocytic leukemia cells and represent potential therapeutic targets

“…45 Moreover, inhibition or downregulation of Abl has been reported to reduce the expression of the anti-apoptotic protein Mcl-1 and induce leukemic cell apoptosis. [45][46] Although we did not observe a direct cytotoxic effect of VX-680 against resting CLL cells, it remains possible that this compound could enhance the sensitivity of these cells to other cytotoxic agents by down-regulating Mcl-1.…”

N-(4-hydroxyphenyl)retinamide promotes apoptosis of resting and proliferating B-cell chronic lymphocytic leukemia cells and potentiates fludarabine and ABT-737 cytotoxicity

“…29 It positively regulates Mcl-1. 28 Its inhibition promoted CLL cell apoptosis. 38 We observed in our 4HPR-treated CLL cells remarkable downregulation of the active phosphorylated form of NF-kB.…”

“…NF-kB, known to positively regulate Mcl-1, 28 is constitutively activated in CLL cells. 29 We examined the effects of 4HPR on NF-kB activity by western blot, because the antibody was not well suitable for flow cytometry.…”