type: paper
title: Depletion of the apical endosome in response to viruses and bacterial toxins provides cell-autonomous host defense at mucosal surfaces
year: 2022
authors:
- Maeda, Keiko
- Zachos, Nicholas C.
- Orzalli, Megan H.
- Schmieder, Stefanie S.
- Chang, Denis
- Bugda Gwilt, Katlynn
- Doucet, Michele
- Baetz, Nicholas W.
- Lee, Sun
- Crawford, Sue E.
- Estes, Mary K.
- Kagan, Jonathan C.
- Turner, Jerrold R.
- Lencer, Wayne I.
journal: Cell Host & Microbe
doi: 10.1016/j.chom.2021.12.011
url: https://linkinghub.elsevier.com/retrieve/pii/S1931312821005825
project:
- Rotation_03
system:
- intestinal_epithelium
- polarized_epithelial_cells
- apical_endosome
- mucosal_barrier
- apical_membrane
disease:
- viral_gastroenteritis
- secretory_diarrhea
- mucosal_infection
genes:
- pard6b
- prkci
- cdc42
processes:
- apical_endocytosis
- endosome_recycling
- epithelial_polarity
- proteasome_degradation
- cell_autonomous_immunity
- pathogen_entry
methods:
- human_intestinal_enteroids
- polarized_monolayer_culture
- receptor_mediated_transcytosis_assay
- shRNA_knockdown
- CRISPR_knockout
- proteomics_mass_spectrometry
- cdc42_activation_assay
key_findings:
- pard6b_degradation
- apkc_degradation
- apical_endosome_suppression
- inhibition_of_apical_pathogen_entry
- glycosphingolipid_sensing
limitations:
- upstream_sensor_unknown
- cdc42_activation_mechanism_unclear
- in_vivo_validation_limited
- pathogen_specificity_unresolved
relevance:
- innate_epithelial_defense_mechanism
- apical_endosome_as_therapeutic_target
- polarity_signaling_in_immunity
concepts:
- apical_endosome_defense_switch
- polarity_complex_regulated_trafficking
- glycosphingolipid_danger_sensing
- cell_autonomous_epithelial_immunity
tags:
- gi
- epithelial_polarity
- endocytosis
- innate_immunity
- trafficking
Polarized epithelial cells form the essential barrier against infection at mucosal surfaces. Many pathogens breach this barrier to cause disease, often by co-opting cellular endocytosis mechanisms to enter the cell through the lumenal (apical) cell surface. We recently discovered that loss of the cell polarity gene PARD6B selectively diminishes apical endosome function. Here, we find that in response to epithelial cell entry of certain viruses and bacterial toxins via the apical membrane, PARD6B and aPKC, two components of the PARD6B-aPKC-Cdc42 apical polarity complex undergo rapid proteasome-dependent degradation. Perturbation of apical membrane glycosphingolipids by toxin or virus binding signals to induce the degradation of PARD6B. The loss of PARD6B causes depletion of apical endosome function and renders the cell resistant to further infection from the lumenal cell surface - thus enabling a form of cell-autonomous host defense.
Apical exposure to viruses or glycosphingolipid-binding toxins induces rapid proteasome-dependent degradation of PARD6B and aPKC
Loss of PARD6B is necessary and sufficient to suppress apical endosome recycling and transcytosis
Basolateral endosome pathways remain intact, preserving epithelial barrier function
Cdc42 activation is required for PARD6B degradation, but not sufficient alone
Apical endosome suppression blocks subsequent viral and toxin entry, conferring cell-autonomous protection
Human intestinal enteroid monolayers to model physiologic epithelial polarity
FcRn-based quantitative transcytosis and recycling assays as a global readout of polarized endosome function
Proteasome inhibition to establish post-translational control
CRISPR and isoform-specific rescue to define PARD6B specificity
Reframes epithelial polarity machinery as an active innate immune sensor
Establishes the apical endosome as a regulated defense node, not a passive trafficking compartment
Demonstrates that epithelial defense can occur without cytokines or immune cells
Suggests membrane lipid organization as an upstream danger-sensing layer
Links diarrheal pathophysiology to deliberate suppression of apical transport
Figure 1: Selective loss of apical protein sorting and apical endosome function during viral exposure
Figure 2–3: Proteasome-dependent degradation of PARD6B and aPKC from apical signaling
Figure 4–5: Glycosphingolipid-binding toxins phenocopy viral effects without replication
Figure 6: Cdc42 activation required for polarity complex degradation
Figure 7: Functional protection against secondary infection via apical route
## Limitations
Molecular sensor linking glycosphingolipid perturbation to Cdc42 activation is undefined
Mechanism coupling Cdc42 activation to proteasomal targeting of PARD6B remains unclear
Limited in vivo validation beyond ex vivo human tissue
Specificity for which pathogens trigger this pathway is incompletely defined