SCF and other cullin-ring ligases (CRLs) have been implicated in numerous human developmental and disease pathways. These enzymes function in the ubiquitin proteolytic pathway, catalyzing the transfer of ubiquitin to specific proteins and thus targeting these proteins for degradation. Previous studies have revealed that SCF activity is highly regulated, with numerous proteins including CAND1, SGT1, the COP9 signalosome (CSN), and the RUB/NEDD8 conjugation pathway all acting to modulate SCF activity. While some understanding into the nature of the regulation by these factors has been achieved, many questions remain, and it seems likely that additional SCF regulatory mechanisms are yet to be discovered. The plant hormone auxin regulates virtually every aspect of plant growth and development. The SCFTIR1 ubiquitin-ligase regulates auxin response by targeting a family of transcriptional repressors for ubiquitin- mediated proteolysis in response to an auxin stimulus. Auxin signaling in the model plant Arabidopsis thaliana is exquisitely sensitive to perturbations in SCFTIR1 activity, and has proven to be an extremely powerful genetic system for studying how eukaryotic organisms regulate SCF ubiquitin-ligase activity. Mutations in virtually every known SCF component and regulator have been isolated in genetic screens for mutants exhibiting reduced auxin response. This system provides several novel genetic tools, including viable mutant alleles of CAND1 and CSN subunits, which are not available in other multicellular eukaryotic model systems. The long-term goal of this project is to thoroughly elucidate the molecular mechanisms underlying auxin- mediated control of plant growth and development. Such knowledge will facilitate the manipulation of plant growth and development to improve food production and other plant traits of benefit to human health. More broadly, SCF complexes and the regulatory mechanisms controlling their activity are highly conserved throughout higher eukaryotes. The proposed studies include genetic, molecular, and biochemical approaches to elucidate the regulatory mechanisms controlling SCFTIR1 activity. First, the control of SCFTIR1 activity by regulated cycles of assembly and disassembly will be examined using novel genetic tools and simple biochemical assays. Second, a novel activity of either the CSN or a unique complex containing the CSN3 subunit that is required for auxin-inducible gene expression will be characterized. Third, a collection of mutants isolated in a genetic screen designed to identify negative regulators of SCF activity will be characterized and incorporated into current models for auxin signaling and SCF regulation. The findings from the proposed experiments will almost certainly have direct parallels to the mechanisms human cells employ to regulate SCF activity and other signaling processes, thus increasing understanding of disease pathogenesis and potentially leading to novel therapeutic strategies for modulating SCF activity in cancer and other diseases.

Public Health Relevance

The highly conserved ubiquitin protein degradation pathway regulates many fundamental cellular processes, and defects in this pathway have been implicated in dozens of human diseases. The model plant Arabidopsis thaliana provides a powerful genetic system for studying conserved biological processes. We will utilize novel genetic tools provided by Arabidopsis to elucidate the mechanisms employed by eukaryotic cells to regulate protein degradation.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM067203-07
Application #
8209054
Study Section
Cellular Signaling and Regulatory Systems Study Section (CSRS)
Program Officer
Reddy, Michael K
Project Start
2003-01-01
Project End
2014-12-31
Budget Start
2012-01-01
Budget End
2012-12-31
Support Year
7
Fiscal Year
2012
Total Cost
$266,466
Indirect Cost
$82,466
Name
University of Minnesota Twin Cities
Department
Other Basic Sciences
Type
Schools of Arts and Sciences
DUNS #
555917996
City
Minneapolis
State
MN
Country
United States
Zip Code
55455
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Vi, Son Lang; Trost, Gerda; Lange, Peggy et al. (2013) Target specificity among canonical nuclear poly(A) polymerases in plants modulates organ growth and pathogen response. Proc Natl Acad Sci U S A 110:13994-9
Huang, He; Quint, Marcel; Gray, William M (2013) The eta7/csn3-3 auxin response mutant of Arabidopsis defines a novel function for the CSN3 subunit of the COP9 signalosome. PLoS One 8:e66578
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Franklin, Keara A; Lee, Sang Ho; Patel, Dhaval et al. (2011) Phytochrome-interacting factor 4 (PIF4) regulates auxin biosynthesis at high temperature. Proc Natl Acad Sci U S A 108:20231-5
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Parry, G; Calderon-Villalobos, L I; Prigge, M et al. (2009) Complex regulation of the TIR1/AFB family of auxin receptors. Proc Natl Acad Sci U S A 106:22540-5
Quint, Marcel; Barkawi, Lana S; Fan, Kai-Ting et al. (2009) Arabidopsis IAR4 modulates auxin response by regulating auxin homeostasis. Plant Physiol 150:748-58
Spartz, Angela K; Gray, William M (2008) Plant hormone receptors: new perceptions. Genes Dev 22:2139-48

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