Role of FBXO24 mediated ubiquitination of FoxP1 protein in the pathogenesis and treatment of COPD

PROJECT SUMMARY/ABSTRACT
COPD is the fourth leading cause of death in the US; however, we do not fully understand the pathogenesis of
COPD and lack disease-modifying therapies. Forkhead box protein P1 (FoxP1) is a transcriptional repressor that
participates in lung epithelial development. Recent data from the UK Biobank, ECLIPSE, and COPDGene
cohorts implicate FoxP1 as an important predictor of airflow limitation. However, a role for FoxP1 in the
pathogenesis of COPD remains unexamined.
Preliminary work suggests that FoxP1 protein is reduced while FoxP1 mRNA is increased in the lungs of
humans and mice with COPD compared with controls. Specifically, we find that exposure to cigarette smoke
causes the E3 ligase FBXO24 to ubiquitinate FoxP1, resulting in its proteasomal degradation in lung epithelial
cells in vitro. The resulting loss of FoxP1 protein increases FoxP1 mRNA because FoxP1 is known to repress
its own promoter. Unexpectedly, loss of FoxP1 protein increases activity of the unfolded protein response (UPR)
as well as levels of the UPR’s apoptosis inducer C/EBP-homologous protein (CHOP) in lung epithelial cells.
Analyses of publicly available FoxP1 ChIP-seq data demonstrates significant enrichment for FoxP1 binding sites
in the promoters of key UPR genes and CHOP in human embryonic stem cells and HepG2 cells. Further,
computational studies identify high probability binding sites for FoxP1 in the DNA sequence of UPR and CHOP
promoters. In vivo, deletion of CHOP reduces apoptosis and emphysema in the lung. Finally, inducible deletion
of FoxP1 by intranasal administration of Cre expressing adenovirus to floxed FoxP1 mice increased cigarette
smoke induced emphysema. Therefore, we hypothesize that cigarette smoke causes FBXO24 to ubiquitinate
and degrade FoxP1 protein in the lung epithelium thereby increasing promotor activity for key UPR genes and
CHOP and inducing apoptosis and emphysema.
During this award, we will: (1) Test the hypothesis that FoxP1 binds to and suppresses the promoters of
key UPR genes and CHOP in lung epithelial cells by CUT&RUN and luciferase reporter assays, as well as map
FoxP1 binding sites via promoter mutagenesis studies; (2) Test the hypothesis that deleting the FoxP1 gene in
the lung epithelium will increase cigarette smoke induced UPR activity, CHOP, and apoptosis in the lung
epithelium, and increase emphysema; and (3) Test the hypothesis that deleting the FBXO24 gene will prevent
cigarette smoke induced degradation of FoxP1 protein and reduce cigarette smoke induced UPR activity, CHOP
and apoptosis in the lung epithelium, and decrease emphysema. This proposal will investigate the mechanism
for a novel link between FoxP1 and the UPR, demonstrate the functional impact of this mechanism in vivo, and
test the efficacy of counteracting FBXO24 as a therapeutic strategy for COPD in preclinical models. This proposal
reflects our long-term objective of developing new mechanism-based therapies that may have unprecedented
disease modifying ability in COPD.

Grant Number: 5R01HL153400-05
NIH Institute/Center: NIH
Principal Investigator: Divay Chandra