TY - JOUR
T1 - BECN1 and BIM interactions with MCL-1 determine fludarabine resistance in leukemic B cells
AU - Sharma, A.
AU - Singh, K.
AU - Mazumder, S.
AU - Hill, B. T.
AU - Kalaycio, M.
AU - Almasan, A.
N1 - Funding Information:
Acknowledgements. This work was supported by a research grant from National Institutes of Health (CA127264; awarded to AA), a US Department of Defense Post-doctoral Training Award (PC094405; awarded to KS) and a fellowship from Cleveland State University (Molecular Medicine Program to AS).
PY - 2013/5
Y1 - 2013/5
N2 - The purine analog fludarabine (Fd) is an essential therapeutic for chronic lymphocytic leukemia (CLL). Innate or acquired resistance to Fd is a significant clinical problem and is largely mediated by increased expression of BCL-2 family members. The antiapoptotic BCL-2 family proteins inhibit both apoptosis and autophagy, therefore, downregulation of antiapoptotic BCL-2 family proteins and enhanced autophagy must coexist in cells dying in response to an apoptosis inducing therapeutic. However, in the drug-resistant cells that have an increased dependence on antiapoptotic proteins, whether autophagy is also inhibited remains unclear. Here, we examined the role of the BCL-2 family in regulating cell death and autophagy in leukemic cell lines and their derivative isogenic Fd-resistant (FdR) cells. MCL-1 degradation following Fd treatment freed the proapoptotic effectors BIM and BECN1, thus leading to cell death-associated autophagy in Fd-sensitive cells. However, in FdR cells, low BIM expression and BECN1 sequestration by MCL-1 prevented cell death. Consistently, in sensitive cells inhibition of apoptosis using siBIM and of both the early-phase autophagy nucleation steps by siBECN1, shATG7 or 3-methyladenine and the late-phase autophagy by shLAMP2, significantly reduced Fd-induced cell death. Paradoxically, FdR cells were addicted to basal autophagy, which was dependent on AMP-activated protein kinase (AMPK) but not BECN1. Moreover, in FdR cells, inhibition of autophagy by shLAMP2, but not siBECN1, enhanced cell death. The BH3-mimetic obatoclax released BIM and BECN1 from MCL-1 in Fd-sensitive and BECN1 from MCL-1 in FdR cells, and was effective at killing both Fd-sensitive and-resistant leukemic cells, including primary CLL cells. Therefore, a differential regulation of autophagy through BECN1 and AMPK signaling in Fd-sensitive and-resistant cells determines the different possible outcomes of autophagy inhibition. These findings suggest effective means to overcome Fd resistance by induction of BIM-dependent apoptosis and activation of BECN1-dependent autophagy.
AB - The purine analog fludarabine (Fd) is an essential therapeutic for chronic lymphocytic leukemia (CLL). Innate or acquired resistance to Fd is a significant clinical problem and is largely mediated by increased expression of BCL-2 family members. The antiapoptotic BCL-2 family proteins inhibit both apoptosis and autophagy, therefore, downregulation of antiapoptotic BCL-2 family proteins and enhanced autophagy must coexist in cells dying in response to an apoptosis inducing therapeutic. However, in the drug-resistant cells that have an increased dependence on antiapoptotic proteins, whether autophagy is also inhibited remains unclear. Here, we examined the role of the BCL-2 family in regulating cell death and autophagy in leukemic cell lines and their derivative isogenic Fd-resistant (FdR) cells. MCL-1 degradation following Fd treatment freed the proapoptotic effectors BIM and BECN1, thus leading to cell death-associated autophagy in Fd-sensitive cells. However, in FdR cells, low BIM expression and BECN1 sequestration by MCL-1 prevented cell death. Consistently, in sensitive cells inhibition of apoptosis using siBIM and of both the early-phase autophagy nucleation steps by siBECN1, shATG7 or 3-methyladenine and the late-phase autophagy by shLAMP2, significantly reduced Fd-induced cell death. Paradoxically, FdR cells were addicted to basal autophagy, which was dependent on AMP-activated protein kinase (AMPK) but not BECN1. Moreover, in FdR cells, inhibition of autophagy by shLAMP2, but not siBECN1, enhanced cell death. The BH3-mimetic obatoclax released BIM and BECN1 from MCL-1 in Fd-sensitive and BECN1 from MCL-1 in FdR cells, and was effective at killing both Fd-sensitive and-resistant leukemic cells, including primary CLL cells. Therefore, a differential regulation of autophagy through BECN1 and AMPK signaling in Fd-sensitive and-resistant cells determines the different possible outcomes of autophagy inhibition. These findings suggest effective means to overcome Fd resistance by induction of BIM-dependent apoptosis and activation of BECN1-dependent autophagy.
KW - Autophagy
KW - BECN1
KW - BIM
KW - Fludarabine resistance
KW - MCL-1
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U2 - 10.1038/cddis.2013.155
DO - 10.1038/cddis.2013.155
M3 - Article
C2 - 23681223
AN - SCOPUS:84879384943
SN - 2041-4889
VL - 4
JO - Cell Death and Disease
JF - Cell Death and Disease
IS - 5
M1 - e628
ER -