Multiple BH3 Mimetics Antagonize Antiapoptotic MCL1 Protein by Inducing the Endoplasmic Reticulum Stress Response and Up-regulating BH3-only Protein NOXA

Tina C Albershardt,Bethany L Salerni,Ryan S Soderquist,Darcy J.P Bates,Alexandre A Pletnev,Alexei F Kisselev,Alan Eastman

doi:10.1074/jbc.m111.255828

Tina C Albershardt, Bethany L Salerni + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m111.255828

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Abstract

BH3 mimetics are small molecules designed or discovered to mimic the binding of BH3-only proteins to the hydrophobic groove of antiapoptotic BCL2 proteins. The selectivity of these molecules for BCL2, BCL-X(L), or MCL1 has been established in vitro; whether they inhibit these proteins in cells has not been rigorously investigated. In this study, we used a panel of leukemia cell lines to assess the ability of seven putative BH3 mimetics to inhibit antiapoptotic proteins in a cell-based system. We show that ABT-737 is the only BH3 mimetic that inhibits BCL2 as assessed by displacement of BAD and BIM from BCL2. The other six BH3 mimetics activate the endoplasmic reticulum stress response inducing ATF4, ATF3, and NOXA, which can then bind to and inhibit MCL1. In most cancer cells, inhibition of one antiapoptotic protein does not acutely induce apoptosis. However, by combining two BH3 mimetics, one that inhibits BCL2 and one that induces NOXA, apoptosis is induced within 6 h in a BAX/BAK-dependent manner. Because MCL1 is a major mechanism of resistance to ABT-737, these results suggest a novel strategy to overcome this resistance. Our findings highlight a novel signaling pathway through which many BH3 mimetics inhibit MCL1 and suggest the potential use of these agents as adjuvants in combination with various chemotherapy strategies.

Highlights

The evasion of apoptosis has been recognized as one of the hallmarks of cancer [3], making pharmacological inhibition of antiapoptotic proteins a potential strategy to induce apoptosis in cancer cells
The ability of other BH3 mimetics to inhibit antiapoptotic proteins is currently questioned because they kill cells in a BAX/BAK-independent manner [8, 11]
When used as a single agent, some of the BH3 mimetics induce BAX/BAK-dependent apoptosis within 24 h, this dependence diminishes at later time points

Summary

Introduction

The evasion of apoptosis has been recognized as one of the hallmarks of cancer [3], making pharmacological inhibition of antiapoptotic proteins a potential strategy to induce apoptosis in cancer cells. These results suggest that BAD is constitutively bound to BCL2 in many cell lines and that the disruption of this binding by ABT-737 provides a rapid and quantitative readout for the functional inhibition of BCL2 in a cell-based system. Most BH3 Mimetics Induce NOXA—While investigating the translocation of BAD, we observed that NOXA was elevated in a concentration-dependent manner by all of the BH3 mimetics except ABT-737; MCL1 was concurrently induced

Results

Conclusion