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Current Biology : CB May 2021Cells of the innate immune system, notably macrophages, neutrophils and dendritic cells, perform essential antimicrobial and homeostatic functions. These functions rely... (Review)
Review
Cells of the innate immune system, notably macrophages, neutrophils and dendritic cells, perform essential antimicrobial and homeostatic functions. These functions rely on the dynamic surveillance of the environment supported by the formation of elaborate membrane protrusions. Such protrusions - pseudopodia, lamellipodia and filopodia - facilitate the sampling of the surrounding fluid by macropinocytosis, as well as the engulfment of particulates by phagocytosis. Both processes entail extreme plasma membrane deformations that require the coordinated rearrangement of cytoskeletal polymers, which exert protrusive force and drive membrane coalescence and scission. The resulting vacuolar compartments undergo pronounced remodeling and ultimate resolution by mechanisms that also involve the cytoskeleton. Here, we describe the regulation and functions of cytoskeletal assembly and remodeling during macropinocytosis and phagocytosis.
Topics: Animals; Cytoskeleton; Dendritic Cells; Humans; Macrophages; Neutrophils; Phagocytosis; Pinocytosis; Pseudopodia
PubMed: 34033794
DOI: 10.1016/j.cub.2021.01.036 -
Cancer Cell May 2021Many cancers, including pancreatic ductal adenocarcinoma (PDAC), depend on autophagy-mediated scavenging and recycling of intracellular macromolecules, suggesting that...
Many cancers, including pancreatic ductal adenocarcinoma (PDAC), depend on autophagy-mediated scavenging and recycling of intracellular macromolecules, suggesting that autophagy blockade should cause tumor starvation and regression. However, until now autophagy-inhibiting monotherapies have not demonstrated potent anti-cancer activity. We now show that autophagy blockade prompts established PDAC to upregulate and utilize an alternative nutrient procurement pathway: macropinocytosis (MP) that allows tumor cells to extract nutrients from extracellular sources and use them for energy generation. The autophagy to MP switch, which may be evolutionarily conserved and not cancer cell restricted, depends on activation of transcription factor NRF2 by the autophagy adaptor p62/SQSTM1. NRF2 activation by oncogenic mutations, hypoxia, and oxidative stress also results in MP upregulation. Inhibition of MP in autophagy-compromised PDAC elicits dramatic metabolic decline and regression of transplanted and autochthonous tumors, suggesting the therapeutic promise of combining autophagy and MP inhibitors in the clinic.
Topics: Animals; Autophagy; Carcinoma, Pancreatic Ductal; Mice; NF-E2-Related Factor 2; Oxidative Stress; Pancreatic Neoplasms; Pinocytosis; Sequestosome-1 Protein; Signal Transduction
PubMed: 33740421
DOI: 10.1016/j.ccell.2021.02.016 -
Cells & Development Dec 2021Macropinocytosis is a form of endocytosis performed by ruffles and cups of the plasma membrane. These close to entrap droplets of medium into micron-sized vesicles,... (Review)
Review
Macropinocytosis is a form of endocytosis performed by ruffles and cups of the plasma membrane. These close to entrap droplets of medium into micron-sized vesicles, which are trafficked through the endocytic system, their contents digested and useful products absorbed. Macropinocytosis is constitutive in certain immune cells and stimulated in many other cells by growth factors. It occurs across the animal kingdom and in amoebae, implying a deep evolutionary history. Its scientific history goes back 100 years, but increasingly work is focused on its medical importance in the immune system, cancer cell feeding, and as a backdoor into cells for viruses and drugs. Macropinocytosis is driven by the actin cytoskeleton whose dynamics can be appreciated with lattice light sheet microscopy: this reveals a surprising variety of routes for forming macropinosomes. In Dictyostelium amoebae, macropinocytic cups are organized around domains of PIP3 and active Ras and Rac in the plasma membrane. These attract activators of the Arp2/3 complex to their periphery, creating rings of actin polymerization that shape the cups. The size of PIP3 domains is controlled by RasGAPs, such as NF1, and the lipid phosphatase, PTEN. It is likely that domain dynamics determine the shape, evolution and closing of macropinocytic structures.
Topics: Actin Cytoskeleton; Amoeba; Animals; Biology; Dictyostelium; Endocytosis; Pinocytosis
PubMed: 34175511
DOI: 10.1016/j.cdev.2021.203713 -
British Journal of Cancer Jan 2021A potentially important aspect in the regulation of tumour metastasis is endocytosis. This process consists of internalisation of cell-surface receptors via pinocytosis,... (Review)
Review
A potentially important aspect in the regulation of tumour metastasis is endocytosis. This process consists of internalisation of cell-surface receptors via pinocytosis, phagocytosis or receptor-mediated endocytosis, the latter of which includes clathrin-, caveolae- and non-clathrin or caveolae-mediated mechanisms. Endocytosis then progresses through several intracellular compartments for sorting and routing of cargo, ending in lysosomal degradation, recycling back to the cell surface or secretion. Multiple endocytic proteins are dysregulated in cancer and regulate tumour metastasis, particularly migration and invasion. Importantly, four metastasis suppressor genes function in part by regulating endocytosis, namely, the NME, KAI, MTSS1 and KISS1 pathways. Data on metastasis suppressors identify a new point of dysregulation operative in tumour metastasis, alterations in signalling through endocytosis. This review will focus on the multicomponent process of endocytosis affecting different steps of metastasis and how metastatic-suppressor genes use endocytosis to suppress metastasis.
Topics: Cell Movement; Endocytosis; Humans; Neoplasm Invasiveness; Neoplasms
PubMed: 33262521
DOI: 10.1038/s41416-020-01179-8 -
Nature Communications Feb 2022Hepatocellular carcinoma (HCC) invariably exhibits inadequate O (hypoxia) and nutrient supply. Hypoxia-inducible factor (HIF) mediates cascades of molecular events that...
Hepatocellular carcinoma (HCC) invariably exhibits inadequate O (hypoxia) and nutrient supply. Hypoxia-inducible factor (HIF) mediates cascades of molecular events that enable cancer cells to adapt and propagate. Macropinocytosis is an endocytic process initiated by membrane ruffling, causing the engulfment of extracellular fluids (proteins), protein digestion and subsequent incorporation into the biomass. We show that macropinocytosis occurs universally in HCC under hypoxia. HIF-1 activates the transcription of a membrane ruffling protein, EH domain-containing protein 2 (EHD2), to initiate macropinocytosis. Knockout of HIF-1 or EHD2 represses hypoxia-induced macropinocytosis and prevents hypoxic HCC cells from scavenging protein that support cell growth. Germline or somatic deletion of Ehd2 suppresses macropinocytosis and HCC development in mice. Intriguingly, EHD2 is overexpressed in HCC. Consistently, HIF-1 or macropinocytosis inhibitor suppresses macropinocytosis and HCC development. Thus, we show that hypoxia induces macropinocytosis through the HIF/EHD2 pathway in HCC cells, harnessing extracellular protein as a nutrient to survive.
Topics: Animals; Carcinoma, Hepatocellular; Carrier Proteins; Cell Line, Tumor; Gene Expression Regulation, Neoplastic; Gene Knockdown Techniques; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Liver Neoplasms; Mice; Mice, Knockout; Pinocytosis; Proof of Concept Study; Tumor Hypoxia; Xenograft Model Antitumor Assays
PubMed: 35177645
DOI: 10.1038/s41467-022-28618-9 -
Proceedings of the National Academy of... Jul 2021AXL, a member of the TAM (TYRO3, AXL, MER) receptor tyrosine kinase family, and its ligand, GAS6, are implicated in oncogenesis and metastasis of many cancer types....
AXL, a member of the TAM (TYRO3, AXL, MER) receptor tyrosine kinase family, and its ligand, GAS6, are implicated in oncogenesis and metastasis of many cancer types. However, the exact cellular processes activated by GAS6-AXL remain largely unexplored. Here, we identified an interactome of AXL and revealed its associations with proteins regulating actin dynamics. Consistently, GAS6-mediated AXL activation triggered actin remodeling manifested by peripheral membrane ruffling and circular dorsal ruffles (CDRs). This further promoted macropinocytosis that mediated the internalization of GAS6-AXL complexes and sustained survival of glioblastoma cells grown under glutamine-deprived conditions. GAS6-induced CDRs contributed to focal adhesion turnover, cell spreading, and elongation. Consequently, AXL activation by GAS6 drove invasion of cancer cells in a spheroid model. All these processes required the kinase activity of AXL, but not TYRO3, and downstream activation of PI3K and RAC1. We propose that GAS6-AXL signaling induces multiple actin-driven cytoskeletal rearrangements that contribute to cancer-cell invasion.
Topics: Actin Cytoskeleton; Actins; Cell Line, Tumor; Cell Proliferation; Cell Surface Extensions; Enzyme Activation; Focal Adhesions; Glioblastoma; Glutamine; HEK293 Cells; Humans; Intercellular Signaling Peptides and Proteins; Models, Biological; Neoplasm Invasiveness; Neoplasms; Phosphatidylinositol 3-Kinases; Pinocytosis; Protein Binding; Proto-Oncogene Proteins; Receptor Protein-Tyrosine Kinases; Signal Transduction; rac1 GTP-Binding Protein; Axl Receptor Tyrosine Kinase
PubMed: 34244439
DOI: 10.1073/pnas.2024596118 -
Proceedings of the National Academy of... Jan 2021During pregnancy, the appropriate allocation of nutrients between the mother and the fetus is dominated by maternal-fetal interactions, which is primarily governed by...
During pregnancy, the appropriate allocation of nutrients between the mother and the fetus is dominated by maternal-fetal interactions, which is primarily governed by the placenta. The syncytiotrophoblast (STB) lining at the outer surface of the placental villi is directly bathed in maternal blood and controls feto-maternal exchange. The STB is the largest multinucleated cell type in the human body, and is formed through syncytialization of the mononucleated cytotrophoblast. However, the physiological advantage of forming such an extensively multinucleated cellular structure remains poorly understood. Here, we discover that the STB uniquely adapts to nutrient stress by inducing the macropinocytosis machinery through repression of mammalian target of rapamycin (mTOR) signaling. In primary human trophoblasts and in trophoblast cell lines, differentiation toward a syncytium triggers macropinocytosis, which is greatly enhanced during amino acid shortage, induced by inhibiting mTOR signaling. Moreover, inhibiting mTOR in pregnant mice markedly stimulates macropinocytosis in the syncytium. Blocking macropinocytosis worsens the phenotypes of fetal growth restriction caused by mTOR-inhibition. Consistently, placentas derived from fetal growth restriction patients display: 1) Repressed mTOR signaling, 2) increased syncytialization, and 3) enhanced macropinocytosis. Together, our findings suggest that the unique ability of STB to undergo macropinocytosis serves as an essential adaptation to the cellular nutrient status, and support fetal survival and growth under nutrient deprivation.
Topics: AMP-Activated Protein Kinases; Adaptation, Physiological; Amino Acids; Animals; Cell Line; Cell Nucleus; Chorionic Villi; Female; Fetal Growth Retardation; Gene Expression Regulation; Humans; Maternal-Fetal Exchange; Mice; Pinocytosis; Pregnancy; Pregnancy Proteins; Primary Cell Culture; Ribosomal Protein S6 Kinases, 70-kDa; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Trophoblasts
PubMed: 33402432
DOI: 10.1073/pnas.2017092118 -
Journal of Experimental & Clinical... Mar 2022Macropinocytosis, an important nutrient-scavenging pathway in certain cancer cells, allows cells to compensate for intracellular amino acid deficiency under...
BACKGROUND
Macropinocytosis, an important nutrient-scavenging pathway in certain cancer cells, allows cells to compensate for intracellular amino acid deficiency under nutrient-poor conditions. Ferroptosis caused by cysteine depletion plays a pivotal role in sorafenib responses during hepatocellular carcinoma (HCC) therapy. However, it is not known whether macropinocytosis functions as an alternative pathway to acquire cysteine in sorafenib-treated HCC, and whether it subsequently mitigates sorafenib-induced ferroptosis. This study aimed to investigate whether sorafenib drives macropinocytosis induction, and how macropinocytosis confers ferroptosis resistance on HCC cells.
METHODS
Macropinocytosis, both in HCC cells and HCC tissues, was evaluated by measuring TMR-dextran uptake or lysosomal degradation of DQ-BSA, and ferroptosis was evaluated via C11-BODIPY fluorescence and 4-HNE staining. Sorafenib-induced ferroptosis and macropinocytosis were validated in tumor tissues taken from HCC patients who underwent ultrasound-guided needle biopsy.
RESULTS
Sorafenib increased macropinocytosis in human HCC specimens and xenografted HCC tissues. Sorafenib-induced mitochondrial dysfunction was responsible for activation of PI3K-RAC1-PAK1 signaling, and amplified macropinocytosis in HCC. Importantly, macropinocytosis prevented sorafenib-induced ferroptosis by replenishing intracellular cysteine that was depleted by sorafenib treatment; this rendered HCC cells resistant to sorafenib. Finally, inhibition of macropinocytosis by amiloride markedly enhanced the anti-tumor effect of sorafenib, and sensitized resistant tumors to sorafenib.
CONCLUSION
In summary, sorafenib induced macropinocytosis, which conferred drug resistance by mitigating sorafenib-induced ferroptosis. Thus, targeting macropinocytosis is a promising therapeutic strategy to facilitate ferroptosis-based therapy for HCC.
Topics: Animals; Carcinoma, Hepatocellular; Cysteine; Female; Ferroptosis; Humans; Liver Neoplasms; Male; Mice; Pinocytosis; Protein Kinase Inhibitors; Sorafenib
PubMed: 35287706
DOI: 10.1186/s13046-022-02296-3 -
Cancer Discovery Jan 2020Allele-specific signaling by different KRAS alleles remains poorly understood. The mutation displays uneven prevalence among cancers that harbor the highest occurrence...
Allele-specific signaling by different KRAS alleles remains poorly understood. The mutation displays uneven prevalence among cancers that harbor the highest occurrence of mutations: It is rare (∼1%) in lung and colorectal cancers, yet relatively common (∼20%) in pancreatic ductal adenocarcinoma (PDAC), suggesting context-specific properties. We evaluated whether KRAS is functionally distinct from the more common KRAS- or KRAS-mutant proteins (KRAS). We found that KRAS but not KRAS drives macropinocytosis and that MYC is essential for macropinocytosis in KRAS- but not KRAS-mutant PDAC. Surprisingly, we found that KRAS is defective for interaction with a key effector, p110α PI3K (PI3Kα), due to structural perturbations in switch II. Instead, upregulated KRAS-independent PI3Kγ activity was able to support macropinocytosis in KRAS-mutant PDAC. Finally, we determined that KRAS-mutant PDAC displayed a distinct drug sensitivity profile compared with KRAS-mutant PDAC but is still responsive to the combined inhibition of ERK and autophagy. SIGNIFICANCE: We determined that KRAS is impaired in activating a key effector, p110α PI3K. As such, KRAS is impaired in driving macropinocytosis. However, overexpression of PI3Kγ in PDAC compensates for this deficiency, providing one basis for the prevalence of this otherwise rare KRAS mutant in pancreatic cancer but not other cancers...
Topics: Animals; Apoptosis; Biomarkers, Tumor; Carcinoma, Pancreatic Ductal; Cell Proliferation; Class I Phosphatidylinositol 3-Kinases; Female; Gene Expression Regulation, Neoplastic; Humans; Mice; Mice, Inbred NOD; Mice, SCID; Mutation; Pancreatic Neoplasms; Pinocytosis; Proto-Oncogene Proteins p21(ras); Tumor Cells, Cultured; Xenograft Model Antitumor Assays
PubMed: 31649109
DOI: 10.1158/2159-8290.CD-19-1006 -
Current Opinion in Virology Feb 2022Endocytosis is used by eukaryotic cells for ingesting external objects. Importantly, endocytosis is a major process that determines phage pharmacokinetics in vivo.... (Review)
Review
Endocytosis is used by eukaryotic cells for ingesting external objects. Importantly, endocytosis is a major process that determines phage pharmacokinetics in vivo. Either dissemination of phages throughout the system or phage clearance engages cellular uptake of phage particles. Here we discuss phage uptake by mammalian cells, focusing on mechanisms and pathways involved. Of note, cellular uptake of phage virions was first observed in professional phagocytes, such as macrophages or granulocytes. For this reason, it was historically referred to as 'phagocytosis'. The modern definition of phagocytosis, however, identifies this process as a type of endocytosis within a larger repertoire of endocytic pathways, such as macropinocytosis, clathrin-mediated endocytosis, and caveolar endocytosis, which have all been included in the scope of this review.
Topics: Animals; Bacteriophages; Caveolae; Endocytosis; Mammals; Phagocytosis; Pinocytosis
PubMed: 34968792
DOI: 10.1016/j.coviro.2021.12.009