Apoptosis is rapidly triggered by antisense depletion of MCL-1 in differentiating U937 cells

Abstract

Mcl-1 is a member of the Bcl-2 protein family, which has been shown to delay apoptosis in transfection and/or overexpression experiments. As yet no gene knockout mice have been engineered, and so there is little evidence to show that loss of Mcl-1 expression is sufficient to trigger apoptosis. U937 cells constitutively express the antiapoptotic protein Bcl-2; but during differentiation, in response to the phorbol ester PMA (phorbol 12 β-myristate 13 α-acetate), Mcl-1 is transiently induced. The purpose of this investigation was to determine the functional role played by Mcl-1 in this differentiation program. Mcl-1 expression was specifically disrupted by chimeric methylphosphonate/phosphodiester antisense oligodeoxynucleotides to just 5% of control levels. The depletion of Mcl-1 messenger RNA (mRNA) and protein was both rapid and specific, as indicated by the use of control oligodeoxynucleotides and analysis of the expression of otherBCL2 family members and PMA-induced tumor necrosis factor–α (TNF-α). Specific depletion of Mcl-1 mRNA and protein, in the absence of changes in cellular levels of Bcl-2, results in a rapid entry into apoptosis. Levels of the proapoptotic protein Bax remained unchanged during differentiation, while Bak expression doubled within 24 hours. Apoptosis was detected within 4 hours of Mcl-1 antisense treatment by a variety of parameters including a novel live cell imaging technique allowing correlation of antisense treatment and apoptosis in individual cells. The induction of Mcl-1 is required to prevent apoptosis during differentiation of U937 cells, and the constitutive expression of Bcl-2 is unable to compensate for the loss of Mcl-1.

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

“…However, it selectively targets BCL2 but not MCL1. This may confer resistance to this drug, since MCL1 can compensate for the loss of BCL2 function (Moulding et al, 2000). Consistent with this, down-regulation of MCL1 increases the lethality of the BCL2 inhibitor ABT-737 in human leukaemia cells (Chen et al, 2007).…”

Inhibition of myeloid cell leukemia-1: Association with sorafenib-induced apoptosis in human mucoepidermoid carcinoma cells and tumor xenograft

“…Several studies have shown that Mcl-1 plays a critical role in the survival of malignant cancers. 29,30 Indeed, Mcl-1 downregulation may be a critical mechanism for the anticancer activity of many synthetic chemicals. 18,31,32 Our group also recently reported that knockdown of Mcl-1 by tolfenamic acid or Mcl-1 siRNA clearly induced apoptosis in the YD15 MEC cell line.…”

Constitutively Activated Akt-1 Is Vital for the Survival of Human Monocyte-Differentiated Macrophages

“…Mcl-1 phosphorothioate antisense oligonucleotides to Mcl-1 (AS) and control inverted antisense oligonucleotides (INV) were synthesized by Intergrated DNA Technology, Inc. The sequences employed were described previously as Mcl-AS-8 and MclinvAS-8 24. Primary macrophages were incubated with either Mcl-1 AS or INV (100 μM) for 24 h, then harvested, and examined for Mcl-1 expression by Western blot analysis and apoptosis by determination of subdiploid DNA content.…”