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Updated: Jun 23, 2025

Automated Imaging and Analysis for the Quantification of Fluorescently Labeled Macropinosomes
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Leep2A and Leep2B function as a RasGAP complex to regulate macropinosome formation

Xiaoting Chao1,2, Yihong Yang1, Weibin Gong1

  • 1Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.

The Journal of Cell Biology
|June 18, 2024
PubMed

Insights

Researchers discovered Leep2, a Ras GTPase-activating protein (GAP) complex, which is crucial for regulating macropinocytosis, a cellular process for bulk fluid uptake. Fine-tuning Ras activity via Leep2 is essential for proper macropinosome formation.

Area of Science:

  • Cell biology
  • Molecular signaling
  • Biochemistry

Background:

  • Macropinocytosis is a conserved cellular process for bulk fluid uptake, essential for nutrient acquisition and environmental sensing.
  • Ras GTPases are central regulators of macropinocytosis, but their upstream regulation and spatiotemporal control remain unclear.
  • Understanding the molecular mechanisms governing Ras signaling in macropinocytosis is critical for deciphering cellular uptake processes.

Purpose of the Study:

  • To identify novel regulators of macropinocytosis using a proteomics-based approach in the model organism Dictyostelium.
  • To elucidate the role of the identified complex in the spatiotemporal regulation of Ras GTPase activity during macropinosome formation.
  • To investigate how modulation of this complex and its target Ras GTPases affects macropinocytic activity.

Main Methods:

  • Proteomics-based screening in Dictyostelium to identify proteins involved in macropinocytosis regulation.
  • Biochemical assays to characterize the function of the identified Leep2 complex as a Ras GTPase-activating protein (GAP).
  • Genetic manipulation (deletion, overexpression) of Leep2 and target Ras GTPases to assess their impact on macropinocytosis.

Main Results:

  • Identification of Leep2 (composed of Leep2A and Leep2B) as a novel RasGAP complex crucial for macropinocytosis.
  • Localization of the Leep2 complex to forming macropinocytic cups and nascent macropinosomes.
  • Demonstration that Leep2 modulates the activity of three Ras family small GTPases, thereby regulating macropinosome formation.
  • Observed impairment of macropinocytosis upon deletion or overexpression of Leep2, or disruption/sustained activation of target Ras GTPases.

Conclusions:

  • The Leep2 complex plays a critical role in the spatiotemporal regulation of Ras signaling during macropinocytosis.
  • Fine-tuning Ras GTPase activity is essential for efficient and controlled macropinosome formation.
  • This study reveals a key regulatory mechanism governing cellular bulk fluid uptake.

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