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Role of Myeloid Cell Leukemia 1 (MCL-1) in mediating chemoresistance towards BCL-2 homology 3 (BH3) mimetics in lymphoid malignancies

Choudhary, Gaurav Sudhakar
http://orcid.org/0000-0001-5365-6706
http://rave.ohiolink.edu/etdc/view?acc_num=case1448024862

Abstract Details

2016, Doctor of Philosophy, Case Western Reserve University, Pathology.
Overexpression of anti-apoptotic BCL-2 family members is a hallmark of many lymphoid malignancies, including chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL) that can be targeted with the BCL-2 homology (BH)-3 mimetics. In our studies we have investigated novel mechanisms of acquired resistance to the BH3 mimetics, ABT-737 and ABT-199, to develop rational combination therapeutic regimens in response to a resistance determinant MCL-1. ABT-737 and ABT-199 are rationally designed small molecule inhibitors that specifically bind to BCL-2/BCL-xL, but not to MCL-1. I have investigated mechanisms of acquired resistance to ABT-737/ABT-199 therapy, by chronic exposure of leukemic cell lines to ABT-737/ABT-199. Acquired resistance resulted in substantial AKT activation and up-regulation of MCL-1 levels with post-translational modifications on MCL-1 that facilitated both its stabilization and interaction with the BH3-only protein Bim. Resistant cells also failed to activate BAX in response to ABT-737/ABT-199. Additionally, Cyclin E levels were elevated and there was increased association of cyclin E/Cdk2 with MCL-1 in resistant compared to parental cells. Cyclin E depletion led to decreased levels of MCL-1 protein, with no change in MCL-1 mRNA levels. In the absence of cyclin E, MCL-1 ubiquitination was enhanced, leading to decreased protein stability. Studies with MCL-1 phosphorylation mutants show that cyclin E/Cdk2-dependent phosphorylation of MCL-1 residues on its PEST domain resulted in increased MCL-1 stability (Thr92, and Thr163) and Bim binding (Ser64). A genetic approach, through siRNA-mediated down-regulation of Cyclin E, AKT, MCL-1, and BCL-xL, significantly decreased cell survival, demonstrating their importance in conferring ABT-737/ABT-199 resistance. The resistant cells were targeted by the pan-BCL-2 inhibitor gossypol that modulated NOXA/MCL-1 axis. Additionally, the acquired and inherent resistant cells were sensitized to treatment with ABT-737/ABT-199 by inhibitors of the PI3K, AKT, mTOR, and CDK pathways, NVP-BEZ235, GS-1101, and dinaciclib. NVP-BEZ235, a dual inhibitor of p-AKT and mTOR, and the PI3Kd inhibitor GS-1101 (idelalisib) reduced MCL-1 protein levels and sensitized ABT-199 resistant cells to BAX activation. Dinaciclib in combination with ABT-737/ABT-199 resulted in robust synergistic cell death in leukemic cells and primary CLL patient samples. Our findings suggest a novel mechanism that modulates the expression and activity of pro-survival proteins to confer treatment resistance that could be exploited by an effective combined therapeutic regimen for treating MCL-1-dependent tumors.
Alexandru Almasan, Ph.D. (Advisor)
Shigemi Matsuyama, Ph.D. (Committee Chair)
David Danielpour, Ph.D. (Committee Member)
Clark Distelhorst, Ph.D. (Committee Member)
James Jacobberger, Ph.D. (Committee Member)
Clive Hamlin (Other)
145 p.
Molecular Biology; Pathology
MCL-1, BCL-2, BCL-xL, PI3K, ABT-737, ABT-199, Dinaciclib, GS-1101, Akt, Idelalisib, Cdk2, Cyclin E, CLL, B-cell tumor

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Citations

  • Choudhary, G. S. (2016). Role of Myeloid Cell Leukemia 1 (MCL-1) in mediating chemoresistance towards BCL-2 homology 3 (BH3) mimetics in lymphoid malignancies [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1448024862

    APA Style (7th edition)

  • Choudhary, Gaurav. Role of Myeloid Cell Leukemia 1 (MCL-1) in mediating chemoresistance towards BCL-2 homology 3 (BH3) mimetics in lymphoid malignancies. 2016. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1448024862.

    MLA Style (8th edition)

  • Choudhary, Gaurav. "Role of Myeloid Cell Leukemia 1 (MCL-1) in mediating chemoresistance towards BCL-2 homology 3 (BH3) mimetics in lymphoid malignancies." Doctoral dissertation, Case Western Reserve University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1448024862

    Chicago Manual of Style (17th edition)

case1448024862
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© 2016, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.