The BH3-only protein Bim plays a critical role in leukemia cell death triggered by concomitant inhibition of the PI3K/Akt and MEK/ERK1/2 pathways

• Published in: Blood 2009-11, Vol.114 (20), p.4507-4516
• Main Authors: Rahmani, Mohamed, Anderson, Anh, Habibi, Joseph Reza, Crabtree, Timothy Ryan, Mayo, Mandy, Harada, Hisashi, Ferreira-Gonzalez, Andrea, Dent, Paul, Grant, Steven
• Format: Article
• Language: English
• Subjects: Apoptosis - drug effects; Apoptosis - physiology; Apoptosis Regulatory Proteins - metabolism; Bcl-2-Like Protein 11; bcl-Associated Death Protein - metabolism; Biological and medical sciences; DNA Mutational Analysis; Enzyme Inhibitors - pharmacology; Extracellular Signal-Regulated MAP Kinases - drug effects; Extracellular Signal-Regulated MAP Kinases - metabolism; Hematologic and hematopoietic diseases; Humans; Immunoblotting; Immunoprecipitation; Leukemia - metabolism; Leukemia - pathology; Leukemias. Malignant lymphomas. Malignant reticulosis. Myelofibrosis; MAP Kinase Kinase Kinases - drug effects; MAP Kinase Kinase Kinases - metabolism; Medical sciences; Membrane Proteins - metabolism; Myeloid Cell Leukemia Sequence 1 Protein; Myeloid Neoplasia; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-akt - drug effects; Proto-Oncogene Proteins c-akt - metabolism; Proto-Oncogene Proteins c-bcl-2 - metabolism; Signal Transduction - drug effects; Signal Transduction - physiology
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2008-09-177881

Mechanisms underlying apoptosis induced by concomitant interruption of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 (MEK/ERK1/2) and phosphatidylinositol 3-kinase (PI3K)/Akt pathways were investigated in human leukemia cells. Inhibition of these pathways using the MEK inhibitor PD184352 or U0126 and the PI3K/Akt inhibitor perifosine strikingly induced apoptosis in multiple malignant human hematopoietic cells, and substantially reduced the colony-forming capacity of primary acute myeloblastic leukemia, but not normal CD34+ cells. These events were associated with pronounced Bim up-regulation, Mcl-1 down-regulation, marked Bak/Bax conformational change accompanied by Bax membrane translocation, and a pronounced increase in Bax/Bak association. Molecular studies using tet-inducible Akt, constitutively active MEK1, dominant-negative Akt, and MEK1 small interfering RNA revealed that inhibition of both MEK/ERK1/2 and Akt pathways plays a critical functional role in perifosine/PD184352-mediated lethality. Ectopic Mcl-1 expression potently inhibited perifosine/PD184352-induced apoptosis, as did Bak or Bax knockdown. Notably, knockdown of Bim, but not Bad, blocked Bak and Bax conformational change, inhibited Bax membrane translocation, diminished Bax/Bak binding, and sharply attenuated perifosine/PD184352-induced apoptosis. Finally, enforced expression of Bim significantly enhanced apoptosis induced by PI3K/Akt inhibitors, analogous to the effects of MEK1/2 inhibitors. Collectively, these findings suggest that Bim, and Mcl-1, but not Bad, integrate death signaling triggered by concomitant disruption of the PI3K/Akt and MEK1/2/ERK1/2 pathways in human leukemia cells.