Metabolic regulation of KLHL proteins through O-glycosylation - Project Summary/Abstract
The Kelch-like (KLHL) family of proteins are critical substrate adaptors for E3 ubiquitin
ligases and mutations in KLHL genes underlie a range of human diseases, including cancer and
neurodegeneration. However, the upstream regulation and downstream effects of most KLHL
proteins remain poorly understood. The best-characterized KLHL protein is KEAP1, which binds
to the CUL3/RBX1 E3 ligase components to mediate the ubiquitination and destruction of NRF2,
a master transcriptional regulator of redox stress signaling. Redox-active compounds disable
KEAP1, preventing the ubiquitination of NRF2 by KEAP1/CUL3/RBX1 and allowing NRF2
accumulation and activation. Recently, we demonstrated that KEAP1 is modified by O-GlcNAc, a
nutrient-sensitive, reversible form of glycosylation, and this modification is required for efficient
NRF2 ubiquitination and degradation. Blockade of KEAP1 O-GlcNAcylation by chemical inhibition
or nutrient deprivation stabilizes and activates NRF2, revealing a new regulatory link between
nutrient sensing and redox stress signaling. Interestingly, we recently discovered that the KLHL
protein gigaxonin is also O-GlcNAcylated in a nutrient-dependent manner, indicating that
glycosylation of KLHL proteins may be a general regulatory link between metabolic status and
proteostasis. Based on these results, we hypothesize that nutrient-sensitive O-GlcNAcylation of
KLHL proteins regulates proteostasis in response to a range of nutrient levels and metabolic
stresses. To test this hypothesis, we will first exploit KEAP1 as a model KLHL protein to determine
how various stresses impact KEAP1 glycosylation and activity. Next, we will determine how
KEAP1 glycosylation affects the KEAP1/CUL3/RBX1 complex and KEAP1-substrate interactions,
using both targeted biochemical and unbiased proteomic approaches. We will then determine the
functional role of O-GlcNAcylation on gigaxonin, whose mutations cause the fatal human disease
giant axon neuropathy (GAN). Finally, we will elucidate the relationship between gigaxonin
glycosylation and GAN disease phenotypes using murine neuronal and human GAN patient
fibroblast models. The successful completion of our project will provide broad and significant
insights into KLHL protein regulation and function, and may point to new therapeutic opportunities
in neurodegeneration, cancer and other diseases by manipulating KLHL proteins through O-
GlcNAc modulation.
