# Endocytic Trafficking and Cell Signaling in Models of ARC Syndrome

> **NIH NIH R01** · UT SOUTHWESTERN MEDICAL CENTER · 2020 · $332,100

## Abstract

Arthrogryposis-renal dysfunction-cholestasis syndrome (ARC) is an autosomal recessive inherited disorder that
leads to developmental defects in multiple organs systems. Symptoms include stiffness of joints,
developmental defects in kidney and liver, scaly skin, agranular platelets, CNS anomalies and persistent
infections and typically result in fatality within the first year after birth. ARC is caused by mutations in one of
two genes, VPS33B or VPS16B/VIPAS39. The two ARC-linked proteins encoded by these genes are
homologs of two of the six subunits of the HOPS complex, which is critical for the fusion of endosomes with
lysosomes. This suggests that ARC is primarily a defect in membrane fusion events of endocytic pathways. To
dissect the mechanisms that link these endocytic trafficking defects with their physiological consequences in
ARC syndrome, Drosophila models of ARC were generated by mutating Vps33B and Vps16B. Surprisingly,
both mutant lines were homozygous viable and fertile without any obvious developmental defects. However,
both models of ARC syndrome revealed defects after infections: an inability to clear bacteria and severe
hypersensitivity to infections despite an increased synthesis of anti-microbial peptides. This hypersensitivity of
ARC models to infections was reversed by loss of function of the innate immune receptor PGRP-LC, indicating
that the reason of lethality is an out-of-control host innate immune response. Importantly, the requirement of
ARC proteins for the regulation of innate immune signaling is conserved in mammals, as knockdown of
VPS33B caused equivalent defects in mammalian macrophages, including dramatically enhanced pro-
inflammatory responses. Furthermore, we find that activated immune receptors in both fly tissues and
mammalian macrophages get stranded in internal vesicles and possibly serve as the source for the elevated
immune signaling we observe. Together, these findings raise the possibility that despite a primary defect in
membrane trafficking, many of the symptoms of ARC patients may reflect exaggerated signaling. This proposal
aims to investigate the mechanisms by which VPS33B-mediated endosomal maturation influences signaling
and how, in turn, signaling alters endosomal trafficking and triggers shortened life span. Drosophila mutants
eliminating different elements of the IMD pathway downstream of the PGRP-LC receptor will be tested in the
context of Vps33B and Vps16B null alleles. Their effect on reduced life span, elevated immune signaling and
altered endocytic trafficking in ARC mutants will be tested. These genetic experiments will be supplemented by
pharmacological approaches blocking different kinases in the IMD pathway with the goal to suppress the
hypersensitivity we observe in ARC models. Together, these experiments will provide a better understanding of
the molecular mechanisms causing at least some of the symptoms in ARC syndrome and thus have the
potential to significantly change the think...

## Key facts

- **NIH application ID:** 9895825
- **Project number:** 5R01GM120196-04
- **Recipient organization:** UT SOUTHWESTERN MEDICAL CENTER
- **Principal Investigator:** Helmut J Kramer
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $332,100
- **Award type:** 5
- **Project period:** 2017-04-01 → 2021-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9895825

## Citation

> US National Institutes of Health, RePORTER application 9895825, Endocytic Trafficking and Cell Signaling in Models of ARC Syndrome (5R01GM120196-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9895825. Licensed CC0.

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