# Mechanisms of Innate Immune Evasion by Mycobacterium Tuberculosis

> **NIH NIH R01** · WASHINGTON UNIVERSITY · 2020 · $544,535

## Abstract

PROJECT SUMMARY
Mycobacterium tuberculosis (Mtb) is the causative agent of the disease tuberculosis (TB) and the leading
cause of death worldwide from a bacterial infection. The success of Mtb stems from its ability to evade
degradation by macrophages. Recent studies have revealed that macrophages clear microorganisms through
two distinct lysosomal trafficking pathways that involve LC3-marked organelles (2, 3). Xenophagy is a process
by which LC3-marked, double-membrane organelles capture and degrade invading microbes. LC3-associated
phagocytosis (LAP) is similar to xenophagy, but does not involve a double membrane and requires NADPH
oxidase and reactive oxygen species (ROS), which are not necessary for xenophagy. These lysosomal
degradative pathways are activated by microbial ligands that stimulate pathogen recognition receptors (PRRs).
The reason why Mtb, which activates numerous PRRs, fails to provoke substantive LC3-associated
phagolysosomal trafficking is not understood. Our extensive preliminary data strongly suggest that CpsA, an
uncharacterized protein secreted by Mtb, specifically blocks LAP. We hypothesize that CpsA interferes with the
activation of NADPH oxidase, thereby blocking the generation of ROS and the LAP-mediated delivery of Mtb to
the lysosome. Consistent with our hypothesis, we found that Mtb strains lacking cpsA exhibit dramatically
enhanced colocalization with the LC3 marker of LAP and that they are highly attenuated in macrophages and
mice. Moreover, NADPH oxidase and the proteins specifically required for LAP are necessary for
macrophages to kill the cpsA mutant. CpsA contains a LytR-CpsA-Psr (LCP) domain, which is commonly
found in Gram-positive organisms. In Streptococcus pneumoniae and Bacillus subtilis, the LCP domain binds
phosphorylated polyisoprenoid lipids. We modeled the structure of Mtb CpsA using the crystal structures an S.
pneumoniae LCP protein and found that all of the lipid phosphate-binding residues are conserved in Mtb CpsA.
In addition, we found that CpsA can bind the human T-cell leukemia virus type I binding protein 1 (TAX1BP1),
and nuclear dot protein 52 kDa (NDP52). TAX1BP1 and NDP52 are paralogs that are involved in linking
bacterial cargo to the autophagy machinery. Thus, we hypothesize that the ability of CpsA to inhibit the
NADPH oxidase and LAP depends upon binding lipid phosphate and host proteins TAX1BP1 and NDP52. To
test our hypotheses, we will (1) study the pathway by which macrophages kill the cpsA mutant, (2)
characterize the mechanism of action of the CpsA protein, and (3) evaluate the importance of this innate
immune evasion mechanism in vivo. Combined, our studies will elucidate a novel mechanism of immune
evasion by one of the most formidable pathogens. By studying the molecular mechanisms Mtb utilizes to
sabotage host cellular functions, we will make fundamental observations that will aid in the development of
better therapeutics and vaccines for Mtb.

## Key facts

- **NIH application ID:** 9841342
- **Project number:** 5R01AI130454-04
- **Recipient organization:** WASHINGTON UNIVERSITY
- **Principal Investigator:** JENNIFER A PHILIPS
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $544,535
- **Award type:** 5
- **Project period:** 2017-01-01 → 2021-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9841342

## Citation

> US National Institutes of Health, RePORTER application 9841342, Mechanisms of Innate Immune Evasion by Mycobacterium Tuberculosis (5R01AI130454-04). Retrieved via AI Analytics 2026-05-21 from https://api.ai-analytics.org/grant/nih/9841342. Licensed CC0.

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