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ORCHESTRATING PP2A HOLOENZYME ASSEMBLY: FROM NORMAL TO ABNORMAL AND THE THERAPEUTIC OPPORTUNITY IN BETWEEN

Leonard, Daniel J
http://rave.ohiolink.edu/etdc/view?acc_num=case1619527891708312

Abstract Details

2021, Doctor of Philosophy, Case Western Reserve University, Pathology.
Reversible protein phosphorylation is perhaps the most abundant mechanism of communication through which cells regulate proteins to guide cellular processes in response to both intracellular and extracellular cues. The reversibility of post-translational protein phosphorylation is achieved through the dueling function of two enzyme classes known as kinases and phosphatases. Protein Phosphatase 2A (PP2A) encompasses a family of enzymes responsible for a majority of cellular phosphatase activity, acting as a switchboard to relay and regulate nearly all cellular signaling pathways. Despite this broad regulatory footprint, the mechanisms that dictate holoenzyme formation and substrate specificity of the PP2A family remain poorly understood. Insight into these mechanistic details would help define the translational capacity of this class of enzymes to serve as therapeutic targets; a concept that has largely been overlooked despite the natural disease fighting characteristics of this class. Here we demonstrate the structural and biochemical attributes of one PP2A regulatory family, the B56 class, that regulate individual holoenzyme formation and stability. Our structures of the B56a, y, and e, PP2A heterotrimers reveal functional roles for the divergent C-termini between isoforms while also providing insight into the isoform specific dependence of post-translational methylation of the C-terminal tail of the PP2A catalytic subunit. These isoform specific qualities highlight the non-redundant functions of even closely related B regulatory subunits and presents an opportunity for enhancement of selective PP2A functions for substrate specific targeting. We demonstrate how a first-in- class set of small molecule activators of PP2A (SMAPs), selectively stabilize the B56⍺ containing PP2A heterotrimers to drive a PP2A dependent tumor suppression. Investigation of clinical populations amenable to SMAP therapy revealed the inherent resistance of cells harboring the most recurrent PP2A mutation, R183W, to this approach. Mechanistic characterization of this R183W mutation in disrupting PP2A biology revealed that this mutation limited the structural flexibility of the protein thus preventing the binding of the methyltransferase, LCMT-1, from catalyzing methylation of the C-subunit required for subsequent B56a binding. Collectively, these studies expand upon the mechanisms regulating PP2A holoenzyme assembly and substrate specificity while highlighting how the most recurrent PP2A mutation selectively disrupts these steps in PP2A biogenesis and the potential therapeutic opportunities afforded by this method of stabilizing protein complexes to enhance their endogenous disease fighting functions.
David Wald, MD, PhD (Committee Chair)
Goutham Narla, MD, PhD (Advisor)
Derek Taylor, PhD (Advisor)
Mark Jackson, PhD (Committee Member)
Drew Adams, PhD (Committee Member)
246 p.
Cellular Biology; Medicine
Phosphatase, PP2A, Cancer, Cryo-EM, Structure, Therapeutics, R183W, MYC, B56, LCMT-1, PME-1, Biogenesis, Methylation

Recommended Citations

Citations

  • Leonard, D. J. (2021). ORCHESTRATING PP2A HOLOENZYME ASSEMBLY: FROM NORMAL TO ABNORMAL AND THE THERAPEUTIC OPPORTUNITY IN BETWEEN [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1619527891708312

    APA Style (7th edition)

  • Leonard, Daniel. ORCHESTRATING PP2A HOLOENZYME ASSEMBLY: FROM NORMAL TO ABNORMAL AND THE THERAPEUTIC OPPORTUNITY IN BETWEEN. 2021. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1619527891708312.

    MLA Style (8th edition)

  • Leonard, Daniel. "ORCHESTRATING PP2A HOLOENZYME ASSEMBLY: FROM NORMAL TO ABNORMAL AND THE THERAPEUTIC OPPORTUNITY IN BETWEEN." Doctoral dissertation, Case Western Reserve University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1619527891708312

    Chicago Manual of Style (17th edition)

case1619527891708312
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This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.