Intracellular iron homeostasis is a critical cellular process that ensures intracellular iron concentrations are sufficient to perform essential iron-dependent functions in aerobic respiration, DNA replication and repair, and multiple biosynthetic pathways (amino acid, nucleotide, and lipid) while avoiding the toxicity associated with excess iron. We previously identified the E3 ubiquitin ligase FBXL5 as a master regulator of iron homeostasis that was responsible for sensing intracellular iron levels through an N-terminal iron-binding domain and coupling changes in iron concentration to its ability to degrade Iron Regulatory Proteins (IRPs) - RNA binding proteins that the post-transcriptional expression of genes involved iron utilization, transport, and storage. In the proposed work, we will examine the hypothesis that FBLX5 is a key signaling hub that coordinates IRP- mediated gene regulation with variety of other iron metabolic pathways in order to generate an integrated cellular response to iron deficiency.
Specific aim 1 will explore the role of the Fe-S cluster assembly pathways in regulating iron homeostasis by characterizing a novel interaction identified in our laboratory between FBXL5 and the CIA targeting complex, a protein complex required for Fe-S protein biogenesis.
In specific aim 2, we will elucidate the cellular mechanism by which FBXL5 is degraded in iron-depleted cells by defining the roles of the E3 ubiquitin ligase HERC2 and the kinase SPAK in this proteolytic pathway. Finally, specific aim 3 will focus on examining a role for FBXL5 in regulating ferritin degradation via its association with the autophagy adaptor NCOA4. Investigation of these three aims will uncover the molecular mechanisms that govern how FBXL5 integrates and interprets signals transduced through multiple iron-regulated signaling pathways in order to dictate the multi-faceted cellular response to iron availability.

Public Health Relevance

The attachment of the small protein ubiquitin to specific targets in the cell is an important signal for cellular communication and used in a variety of physiological pathways. This proposal focuses on understanding how the ubiquitin system regulates different facets of iron metabolism. Considering defects in ion metabolism have been linked to many diseases including anemias, hemochromatosis, and cancer, elucidating how iron metabolism is regulated by ubiquitin will have important implications for understanding the molecular basis of these disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
2R01GM089778-06
Application #
9030118
Study Section
Cellular Signaling and Regulatory Systems Study Section (CSRS)
Program Officer
Maas, Stefan
Project Start
2010-07-01
Project End
2019-06-30
Budget Start
2015-09-17
Budget End
2016-06-30
Support Year
6
Fiscal Year
2015
Total Cost
$300,393
Indirect Cost
$96,643
Name
University of California Los Angeles
Department
Biochemistry
Type
Schools of Medicine
DUNS #
092530369
City
Los Angeles
State
CA
Country
United States
Zip Code
90095
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