The SCF-Fbw7 ubiquitin ligase targets proteins for destruction by the ubiquitin-proteasome system. Fbw7 is the SCF component that recognizes substrates and brings them into proximity with the ubiquitylation machinery. Fbw7's substrates include proteins with key roles in cell division, growth, and differentiation, and these include broadly acting oncoproteins (Myc, cyclin E, Notch, and Jun). Accordingly, Fbw7 is a tumor suppressor that is commonly mutated in cancers. The research proposed in this application seeks to develop a comprehensive and mechanistic framework for understanding Fbw7 function and how Fbw7 mutations lead to cancer. These studies are needed to understand its mechanisms of tumor suppression and to develop therapy targeting the Fbw7 pathway. Fbw7 binds to substrates via conserved phosphodegron motifs (CPDs). These complex interactions are regulated both by the phosphodegrons themselves and by Fbw7 dimerization. The goals of Aim 1 are to study how Fbw7 dimers and CPDs regulate substrate ubiquitylation, and to ascertain the physiologic functions of Fbw7 dimers. We will accomplish these goals by using in vitro approaches to study Fbw7 binding and substrate ubiquitylation, and by using gene targeting in human cells and mice to study endogenous Fbw7 dimer function. Importantly, the SCF-Fbw7 shares structural and functional features with other cullin-ring ligases (CRLs) implicated in human diseases, including dimerization. The impact of these studies may thus extend beyond the Fbw7 pathway and reveal common mechanisms of CRL function. Fbw7 mutations occur commonly in cancers and often involve Fbw7 arginine residues that contact substrate CPDs. Because Fbw7 targets multiple oncoproteins, its tumor suppression functions are complex and the mechanisms by which Fbw7 mutations promote cancer are poorly understood. However, an in-depth understanding of the molecular pathogenesis of Fbw7 mutations is needed in order to develop therapy targeting the Fbw7 pathway. The goals of this aim are to develop models of Fbw7-associated cancer and to understand how Fbw7 mutations contribute to carcinogenesis. We will approach these goals by using gene targeting in mice and human cells to mimic tumor-derived Fbw7 mutations, and by performing a functional genomic screen in mice to identify genes that cooperate with Fbw7 loss during tumorigenesis. These models will be used to gain a mechanistic understanding of Fbw7 mutations, and they will provide key platforms for future studies of targeted therapy.

Public Health Relevance

Fbw7 is a protein that plays central roles in cell division and cancer by targeting oncogenic proteins for destruction, and many cancers contain Fbw7 mutations that contribute to tumorigenesis. The goals of this proposal are to understand how Fbw7 functions in normal cells and why Fbw7 mutations lead to cancer. This research may increase our understanding of why cancer develops and lead to new cancer treatment strategies.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA084069-13
Application #
8301010
Study Section
Membrane Biology and Protein Processing (MBPP)
Program Officer
Hildesheim, Jeffrey
Project Start
2000-02-16
Project End
2015-07-31
Budget Start
2012-08-01
Budget End
2013-07-31
Support Year
13
Fiscal Year
2012
Total Cost
$354,300
Indirect Cost
$152,993
Name
Fred Hutchinson Cancer Research Center
Department
Type
DUNS #
078200995
City
Seattle
State
WA
Country
United States
Zip Code
98109
Welcker, Markus; Clurman, Bruce E (2014) Oncoprotein ubiquitylation: dimers, degrons, and degradation. Cell Cycle 13:1829-30
Davis, Ryan J; Welcker, Markus; Clurman, Bruce E (2014) Tumor suppression by the Fbw7 ubiquitin ligase: mechanisms and opportunities. Cancer Cell 26:455-64
Hughes, Bridget T; Sidorova, Julia; Swanger, Jherek et al. (2013) Essential role for Cdk2 inhibitory phosphorylation during replication stress revealed by a human Cdk2 knockin mutation. Proc Natl Acad Sci U S A 110:8954-9
Davis, Michael A; Larimore, Elizabeth A; Fissel, Brian M et al. (2013) The SCF-Fbw7 ubiquitin ligase degrades MED13 and MED13L and regulates CDK8 module association with Mediator. Genes Dev 27:151-6
Hizli, Asli A; Chi, Yong; Swanger, Jherek et al. (2013) Phosphorylation of eukaryotic elongation factor 2 (eEF2) by cyclin A-cyclin-dependent kinase 2 regulates its inhibition by eEF2 kinase. Mol Cell Biol 33:596-604
Grim, Jonathan E; Knoblaugh, Sue E; Guthrie, Katherine A et al. (2012) Fbw7 and p53 cooperatively suppress advanced and chromosomally unstable intestinal cancer. Mol Cell Biol 32:2160-7
Welcker, Markus; Larimore, Elizabeth A; Frappier, Lori et al. (2011) Nucleolar targeting of the fbw7 ubiquitin ligase by a pseudosubstrate and glycogen synthase kinase 3. Mol Cell Biol 31:1214-24
Kuppers, Daniel A; Hwang, Harry C; Jackson, Aimee L et al. (2011) Effect of Xpcl1 activation and p27(Kip1) loss on gene expression in murine lymphoma. PLoS One 6:e14758
Minella, A C; Grim, J E; Welcker, M et al. (2007) p53 and SCFFbw7 cooperatively restrain cyclin E-associated genome instability. Oncogene 26:6948-53
O'Neil, Jennifer; Grim, Jonathan; Strack, Peter et al. (2007) FBW7 mutations in leukemic cells mediate NOTCH pathway activation and resistance to gamma-secretase inhibitors. J Exp Med 204:1813-24

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