Related Experiment Video
Updated: Sep 4, 2025
Investigating Mast Cell Secretory Granules; from Biosynthesis to Exocytosis
Published on: January 26, 2015
Spatiotemporal Patterns of Substance P-Bound MRGPRX2 Reveal a Novel Connection Between Macropinosome Resolution and
Pia Lazki-Hagenbach1, Elisabeth Kleeblatt1, Hydar Ali2
1Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Abstract:
MRGPRX2, the human member of the MAS-related G protein coupled receptors (Mrgprs), serves as the cellular target of human mast cells (MCs) for innate ligands, including neuropeptides and antimicrobial peptides. In addition, MRGPRX2 also functions as the receptor for multiple FDA-approved drugs. As such, MRGPRX2 is a mediator of MC responses in neurogenic inflammation, host defense and pseudoallergy. We analyzed the spatiotemporal patterns of MRGPRX2 following its binding of the neuropeptide substance P (SP). Herein, we show that MRGPRX2 internalizes via both endocytosis and macropinocytosis, followed by its distribution between a perinuclear region and the secretory granules (SGs). Further, we show that MRGPRX2-containing macropinosomes undergo resolution by a mechanism that involves dynamin and LC3, giving rise to the incorporation of both LC3 and MRGPRX2 into the SGs. SP then promotes the acidification of the LC3-associated SGs, presumably by stimulating their fusion with lysosomes. Taken together, our results reveal a unique mode of MRGPRX2 trafficking that complements endocytosis and involves macropinocytosis, autophagic machinery-assisted macropinosome resolution and receptor delivery to the SGs.
Insights
The study reveals how MRGPRX2 (MAS-related G protein coupled receptor X2) traffics within mast cells. It utilizes macropinocytosis and autophagy to deliver the receptor to secretory granules, impacting immune responses.
Area of Science:
- Immunology
- Cell Biology
- Pharmacology
Background:
- MRGPRX2 is a key receptor on human mast cells, mediating responses to innate ligands and drugs.
- It plays a role in neurogenic inflammation, host defense, and pseudoallergy.
Purpose of the Study:
- To investigate the spatiotemporal trafficking patterns of MRGPRX2 after binding to substance P (SP).
- To elucidate the mechanisms of MRGPRX2 internalization and delivery to secretory granules.
Main Methods:
- Analysis of MRGPRX2 localization and trafficking in response to SP.
- Investigation of endocytosis, macropinocytosis, and autophagic pathways involved in MRGPRX2 transport.
- Microscopy and biochemical assays to track receptor distribution and granule acidification.
Main Results:
- MRGPRX2 internalizes via both endocytosis and macropinocytosis.
- MRGPRX2 is distributed to perinuclear regions and secretory granules (SGs).
- Macropinosomes containing MRGPRX2 are resolved via dynamin and LC3, leading to MRGPRX2 and LC3 incorporation into SGs, followed by SP-induced acidification.
Conclusions:
- MRGPRX2 trafficking involves a novel pathway combining macropinocytosis and autophagic machinery.
- This unique mechanism facilitates receptor delivery to SGs, influencing mast cell responses.
- The findings provide insights into MRGPRX2-mediated pseudoallergy and drug reactions.
