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Matthew Summers, Ph.D.Assistant StaffDepartment of Cancer Biology |
Cell Cycle, Anti-mitotics, Ubiquitin, mechanisms of therapeutic resistance, novel therapeutic targets, biomarkers
Ubiquitin-dependent signaling, mediated by E3 ubiquitin ligases and often associated with protein degradation, is central to many physiological processes. A growing number of the 600-plus E3s are implicated in human diseases, yet only a few have been studied in any detail. Our overall goal is to define mechanisms of ubiquitin-mediated cell cycle control and checkpoint response and, importantly, determine how these processes are misregulated in cancer. We are focused on the Anaphase Promoting Complex (APC), an essential E3 ligase, and master regulator of the cell cycle. Significantly, tumors of multiple origins exhibit deregulated APC activity. Yet, mutations in APC components are infrequent, suggesting that abnormal APC control is the causative force in APC deregulation in cancer. In a central example, the successful treatment of breast cancers with anti-mitotic drugs (e.g. Taxol) depends upon inhibition of the APC in complex with its mitotic activator, Cdc20, (APCCdc20) mediated by the spindle assembly checkpoint (SAC). However, many questions regarding SAC regulation of the APC remain unexplored. Answering these questions is critical for understanding the widely variable response of patients to anti-mitotic therapies and for improving treatment strategies.
Project 1: Defining the role of the spindle assembly checkpoint antagonism in cancer.
Despite the rarity of mutations in SAC components, resistance to anti-mitotics is frequent, suggesting that additional factors impair the SAC and contribute to resistance. Notably, the termination of APCCdc20 inhibition by the SAC requires an active release mechanism that may contribute to. p31Comet is the only clear component of this machinery. We have developed a biochemical assay that recapitulates checkpoint activity and allows us to modulate APC activity by manipulating factors of interest. We have previously used this system to characterize a novel role of UbcH10 in facilitating the checkpoint and are now using it to examine novel factors identified by siRNA and proteomics. Ultimately, a better understanding of this SAC-antagonizing pathway will identify potential biomarkers for predicting sensitivity to anti-mitotics and may identify novel therapeutic targets as well.
Project 2: Determining how antagonism by deubiquitinating enzymes affects APCCdh1 function.
APCCdh1 is an emerging tumor suppressor. Delineating the mechanisms of APCCdh1 regulation is crucial for understanding its tumor suppression function and may open therapeutic avenues aimed at activation of APCCdh1. The goal of this project is to determine the role of APCCdh1-antagonism by ubiquitin-specific proteases (USPs) in cell cycle progression. As negative regulators of ubiquitination, USPs may contribute to diminished APCCdh1 activity in tumors. We have recently identified USP37 as an antagonist of APCCdh1 activity. USP37 is a cell cycle regulated protein that is required for proper accumulation of APC substrates and cell cycle transitions. Using proteomics, biochemical and biological assays, we are defining USP37’s cell cycle function, critical substrates, regulation, and determining the consequences of misregulating USP37.
Routhier EL, Burn TC, Abbaszade I, Summers M, Albright CF, and Prendergast GC. Human Bin3 Complements the F-Actin Localization Defects Caused by Loss of Hob3p, the Fission Yeast Homologue of RVS161p. J. Biol. Chem. 276(24);21670-21677
Corn PG*, Summers MK*, Fogt F, Virmani AK, Gazdar AF, Halazonetis TD, El-Deiry WS. Frequent hypermethylation of the 5' CpG island of the mitotic stress checkpoint gene Chfr in colorectal and non-small cell lung cancer. Carcinogenesis. 24(1):47-51 *authors contributed equally
Bothos J, Summers MK, Venere M, Scolnick DM, and Halazonetis TD. Ubc13-Mms2 is the preferred ubiquitin-conjugating enzyme for the ubiqutin ligase activity of the Chfr mitotic checkpoint protein. Oncogene. 2003 Oct 16;22(46):7101-7
Mariatos G, Bothos J, Zacharatos P, Summers MK, Scolnick DM, Kittas C, Halazonetis TD and Gorgoulis VG. Inactivating mutations targeting the chfr mitotic checkpoint gene in human lung cancer. Cancer Res. 2003 Nov 1;63(21):7185-9
Summers MK, Bothos J, and Halazonetis TD. The Chfr mitotic checkpoint protein arrests cells in early prophase with partially depolymerized lamins and cytoplasmic Cyclin B1. Oncogene, 2005 Apr 14;24(16):2589-98
Tung JJ, Hansen DV, Ban K, Loktev A, Summers MK, and Jackson PK. A Potential Role for the APC inhibitor Emi2, a homolog of Emi1, in Cytostatic Factor Arrest of Xenopus eggs. Proc Natl Acad Sci U S A. 2005 Mar 22;102(12):4318-23
Miller JJ, Summers MK, Hansen DV, Nachury MV, Lehman NL, Loktev A, Jackson PK. Emi1 stably binds and inhibits the anaphase-promoting complex/cyclosome as a pseudosubstrate inhibitor. Genes Dev. 2006 Sep 1;20(17):2410-20
Hansen DV, Pomerening JR, Summers MK, Miller JJ, Ferrell JE Jr, Jackson PK. Emi2 at the crossroads: where CSF meets MPF. Cell Cycle. 2007 Mar; 6(6):732-8
Keck JM, Summers MK, Tedesco D, Ekholm-Reed S, Chuang L, Jackson PK, and Reed SI. Cyclin E deregulation impairs progression through mitosis by inhibiting APCCdh1. J. Cell Biol. 2007 July; 138(3):371-385
Tuttle RL, Bothos J, Summers MK, Luca FC, and Halazonetis TD. Defective in Mitotic Arrest 1/RING Finger 8 is a checkpoint protein that antagonizes the human mitotic exit network. Mol Cancer Res. 2007 Dec;5(12):1304-11
Summers MK, Pan B, Mukhyala K, Jackson PK. The unique N-terminus of the UbcH10 E2 enzyme controls the threshold for APC activation and enhances checkpoint regulation of the APC. Mol Cell. 2008 Aug 22;31(4):544-56
Summers MK and Jackson PK. Biochemical Analysis of the anaphase promoting complex: Activities of E2 enzymes and substrate competitive (“pseudosubstrate”) inhibitors. Methods Mol Biol. 2009 545:313-30.
Peart MJ, Poyurovsky MV, Kass EM, Urist M, Verschuren EW, Summers MK, Jackson PK, and Prives C. APC/CCdc20 targets E2F1 for degradation in prometaphase. Cell Cycle. 2010 Oct 1; 9(19).
Huang X, Summers MK, Pham V, Lill JR, Liu J, Lee G, Kirkpatrick DS, Jackson PK, Fang G, Dixit VM. Deubiquitinase USP37 is activated by CDK2 to antagonize APCCDH1 and promote S-phase entry. Mol.Cell, 2011 May 20;42(4):511-523
Giovinazzi S, Lindsay CR, Morozov VM, Escobar-Cabrera E, Summers MK, Han HS, McIntosh LP, and Ishov AM. Regulation of mitosis and taxane response by Daxx and Rassf1. Oncogene, in press