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Abstract

Biology

Quantitative Assessment of Macropinocytosis in mTORC1-Hyperactive Cells using Flow Cytometry

Published: August 2nd, 2021

DOI:

10.3791/62793

1Pulmonary and Critical Care Medicine, Brigham and Women’s Hospital, Harvard Medical School, 2Metcalf Science Center, Chemistry Department, Boston University

Abstract

Macropinocytosis is a highly conserved, actin-dependent endocytic process that allows the uptake of extracellular material, including proteins and lipids. In proliferating cells, macropinocytosis can deliver extracellular nutrients to the lysosome, processed into critical macromolecule building blocks. Recent studies have highlighted the dependence of multiple cancers on macropinocytosis, including breast, colorectal and pancreatic cancer. Ras mutations are thought to be the driver events behind macropinocytosis initiation, leading to the activation of cellular anabolic processes via the mTORC1 signaling pathway. Interestingly, mTORC1 can also be activated by macropinocytosis independently of Ras. Therefore, macropinocytosis represents a metabolic vulnerability that can be leveraged to target macropinocytic tumors by limiting their access to nutrients therapeutically.

In Tuberous Sclerosis Complex (TSC) and Lymphangioleiomyomatosis (LAM), mTORC1-hyperactivation leads to enhanced macropinocytosis and metabolic reprogramming. Here, we describe a flow cytometry-based protocol to assess macropinocytosis in mammalian cells quantitatively. TSC2-deficient MEFs are employed, which exhibit aberrant activation of mTORC1 and have been shown to have increased macropinocytosis compared to TSC2-expressing cells. Cells treated with pharmacologic inhibitors of macropinocytosis are incubated with fluorescently labeled, lysine-fixable, 70 kDa dextran, or fluorescently labeled bovine serum albumin (BSA) assayed by flow cytometry. To date, robust image-based techniques have been developed to quantitatively assess macropinocytosis in tumor cells in vitro and in vivo. This analysis provides a quantitative assessment of macropinocytosis in multiple experimental conditions and complements existing image-based techniques.

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Keywords Macropinocytosis

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