automated-imaging-analysis-for-quantification-fluorescently-labeled

Automated Imaging and Analysis for the Quantification of Fluorescently Labeled Macropinosomes

Macropinocytosis is a non-specific fluid-phase uptake pathway that allows cells to internalize large extracellular cargo, such as proteins, pathogens, and ...

NCI-designated Cancer Center

Macropinocytosis has emerged as an important nutrient supply pathway that sustains cell growth of cancer cells within the nutrient-poor tumor microenvironment. By internalizing extracellular fluid through this bulk endocytic pathway, albumin is supplied to the cancer cells, which, after degradation, serves as an amino acid source to meet the high nutrient demands of these highly proliferating cells. Here, we describe a streamlined protocol for visualization and quantitation of macropinosomes in adherent cancer cells grown in vitro. The determination of the "macropinocytic index" provides a tool for measuring the extent to which this internalization pathway is utilized within the cancer cells and allows for comparison between different cell lines and treatments. The protocol provided herein has been optimized for reproducibility and is readily adaptable to multiple conditions and settings.

Quantitation of Macropinocytosis in Cancer Cells.

Cancer cells reprogram their metabolism to meet elevated energy demands and favor glycolysis for energy production. This boost in glycolytic flux supports proliferation, but also generates acid in the form of hydrogen ions that must be eliminated from the cytoplasm to maintain the alkaline intracellular pH (pHi) associated with transformation. To cope with acid production, tumor cells employ ion transport systems, including the family of sodium-hydrogen exchangers (NHE). Here, we identify NHE7 as a novel regulator of pHi in pancreatic ductal adenocarcinoma (PDAC). We determine that NHE7 suppression causes alkalinization of the Golgi, leading to a buildup of cytosolic acid that diminishes tumor cell fitness mainly through the dysregulation of actin. Importantly, NHE7 knockdown  leads to the abrogation of tumor growth. These results identify Golgi acidification as a mechanism to control pHi and point to the regulation of pHi as a possible therapeutic vulnerability in PDAC. SIGNIFICANCE: NHE7 regulates cytosolic pH through Golgi acidification, which points to the Golgi as a "proton sink" for metabolic acid. Disruption of cytosolic pH homeostasis via NHE7 suppression compromises PDAC cell viability and tumor growth...

Golgi Acidification by NHE7 Regulates Cytosolic pH Homeostasis in Pancreatic Cancer Cells.

Although pancreatic ductal adenocarcinoma (PDAC) cells are exposed to a nutrient-depleted tumor microenvironment, they can acquire nutrients via macropinocytosis, an endocytic form of protein scavenging that functions to support cancer metabolism. Here, we provide evidence that macropinocytosis is also operational in the pancreatic tumor stroma. We find that glutamine deficiency triggers macropinocytic uptake in pancreatic cancer-associated fibroblasts (CAF). Mechanistically, we decipher that stromal macropinocytosis is potentiated via the enhancement of cytosolic Ca and dependent on ARHGEF2 and CaMKK2-AMPK signaling. We elucidate that macropinocytosis has a dual function in CAFs-it serves as a source of intracellular amino acids that sustain CAF cell fitness and function, and it provides secreted amino acids that promote tumor cell survival. Importantly, we demonstrate that stromal macropinocytosis supports PDAC tumor growth. These results highlight the functional role of macropinocytosis in the tumor stroma and provide a mechanistic understanding of how nutrient deficiency can control stromal protein scavenging. SIGNIFICANCE: Glutamine deprivation drives stromal macropinocytosis to support CAF cell fitness and provide amino acids that sustain PDAC cell survival. Selective disruption of macropinocytosis in CAFs suppresses PDAC tumor growth..

Macropinocytosis in Cancer-Associated Fibroblasts Is Dependent on CaMKK2/ARHGEF2 Signaling and Functions to Support Tumor and Stromal Cell Fitness.

Cancer cells exhibit increased glycolytic flux and adenosine triphosphate (ATP) hydrolysis. These processes increase the acidic burden on the cells through the production of lactate and protons. Nonetheless, cancer cells can maintain an alkaline intracellular pH (pHi) relative to untransformed cells, which sets the stage for optimal functioning of glycolytic enzymes, evasion of cell death, and increased proliferation and motility. Upregulation of plasma membrane transporters allows for H and lactate efflux; however, recent evidence suggests that the acidification of organelles can contribute to maintenance of an alkaline cytosol in cancer cells by siphoning off protons, thereby supporting tumor growth. The Golgi is such an acidic organelle, with resting pH ranging from 6.0 to 6.7. Here, we posit that the Golgi represents a "proton sink" in cancer and delineate the proton channels involved in Golgi acidification and the ion channels that influence this process. Furthermore, we discuss ion channel regulators that can affect Golgi pH and Golgi-dependent processes that may contribute to pHi homeostasis in cancer.

Article	Year
Quantitation of Macropinocytosis in Cancer Cells. Methods in molecular biology (Clifton, N.J.)\| PubMed ID: 30725454	2019
Golgi Acidification by NHE7 Regulates Cytosolic pH Homeostasis in Pancreatic Cancer Cells. Cancer discovery\| PubMed ID: 32200349	2020
Macropinocytosis in Cancer-Associated Fibroblasts Is Dependent on CaMKK2/ARHGEF2 Signaling and Functions to Support Tumor and Stromal Cell Fitness. Cancer discovery\| PubMed ID: 33653692	2021
The Golgi as a "Proton Sink" in Cancer. Frontiers in cell and developmental biology\| PubMed ID: 34055797	2021

Koen M. O. Galenkamp

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