Golgi pH elevation due to loss of V-ATPase subunit V0a2 function correlates with tissue-specific glycosylation changes and globozoospermia.

Loss-of-function variants in ATP6V0A2, encoding the trans Golgi V-ATPase subunit V0a2, cause wrinkly skin syndrome (WSS), a connective tissue disorder with glycosylation defects and aberrant cortical neuron migration. We used knock-out (Atp6v0a2) and knock-in (Atp6v0a2) mice harboring the R755Q missense mutation selectively abolishing V0a2-mediated proton transport to investigate the WSS pathomechanism. Homozygous mutants from both strains displayed a reduction of growth, dermis thickness, and elastic fiber formation compatible with WSS.

Nutrient Levels and Nutrient Sources in Pancreatic Tumors.

It has been known that poor tumor perfusion and dysregulated cancer cell metabolism give rise to tumor microenvironments with unphysiologic nutrient levels, but the precise alterations in metabolite abundance are not well defined. In a 2015 study in Cancer Research, Kamphorst and colleagues published a detailed comparison of the metabolome from human pancreatic tumors and benign tissues. Tumors were depleted in glucose and various nonessential amino acids but, surprisingly, enriched in essential amino acids.

P53-dependent hypusination of eIF5A affects mitochondrial translation and senescence immune surveillance.

Cellular senescence is characterized by a permanent growth arrest and is associated with tissue aging and cancer. Senescent cells secrete a number of different cytokines referred to as the senescence-associated secretory phenotype (SASP), which impacts the surrounding tissue and immune response. Here, we find that senescent cells exhibit higher rates of protein synthesis compared to proliferating cells and identify eIF5A as a crucial regulator of this process.

Lysosomal enzyme trafficking: from molecular mechanisms to human diseases.

Lysosomes degrade and recycle macromolecules that are delivered through the biosynthetic, endocytic, and autophagic routes. Hydrolysis of the different classes of macromolecules is catalyzed by about 70 soluble enzymes that are transported from the Golgi apparatus to lysosomes in a mannose 6-phosphate (M6P)-dependent process. The molecular machinery that generates M6P tags for receptor-mediated targeting of lysosomal enzymes was thought to be understood in detail.

An mTORC1 to HRI signaling axis promotes cytotoxicity of proteasome inhibitors in multiple myeloma.

Multiple myeloma (MM) causes approximately 20% of deaths from blood cancers. Notwithstanding significant therapeutic progress, such as with proteasome inhibitors (PIs), MM remains incurable due to the development of resistance. mTORC1 is a key metabolic regulator, which frequently becomes dysregulated in cancer.

Lysosomal enzyme trafficking factor LYSET enables nutritional usage of extracellular proteins.

Mammalian cells can generate amino acids through macropinocytosis and lysosomal breakdown of extracellular proteins, which is exploited by cancer cells to grow in nutrient-poor tumors. Through genetic screens in defined nutrient conditions, we characterized LYSET, a transmembrane protein (TMEM251) selectively required when cells consume extracellular proteins. LYSET was found to associate in the Golgi with GlcNAc-1-phosphotransferase, which targets catabolic enzymes to lysosomes through mannose-6-phosphate modification.

Direct control of lysosomal catabolic activity by mTORC1 through regulation of V-ATPase assembly.

Mammalian cells can acquire exogenous amino acids through endocytosis and lysosomal catabolism of extracellular proteins. In amino acid-replete environments, nutritional utilization of extracellular proteins is suppressed by the amino acid sensor mechanistic target of rapamycin complex 1 (mTORC1) through an unknown process. Here, we show that mTORC1 blocks lysosomal degradation of extracellular proteins by suppressing V-ATPase-mediated acidification of lysosomes.

Activating mTOR Mutations Are Detrimental in Nutrient-Poor Conditions.

Unlabelled: The mTOR is a key regulator of cell growth that integrates growth factor signaling and nutrient availability and is a downstream effector of oncogenic receptor tyrosine kinases (RTK) and PI3K/Akt signaling. Thus, activating mTOR mutations would be expected to enhance growth in many tumor types. However, tumor sequencing data have shown that mTOR mutations are enriched only in renal clear cell carcinoma, a clinically hypervascular tumor unlikely to be constrained by nutrient availability.

Signaling Pathways that Regulate Macropinocytosis in Mammalian Cells.

Macropinocytosis is an evolutionarily conserved endocytic pathway that mediates non-selective uptake of extracellular fluid in bulk. Macropinocytosis is initiated by localized polymerization of the actin cytoskeleton, which generates plasma membrane protrusions that enclose part of the environment into large endocytic vesicles. From amoebae to mammalian cells, the actin dynamics that drive macropinosome formation are regulated by a conserved set of intracellular signaling proteins including Ras superfamily GTPases and PI3-kinases.

GOLPH3 tunes up glycosphingolipid biosynthesis for cell growth.

Glycosphingolipids are a structurally diverse class of lipids that regulate plasma membrane protein function. Rizzo et al (2021) now show that GOLPH3 promotes intra-Golgi transport of several enzymes that function at branching points of sphingolipid biosynthesis. By regulating the cellular sphingolipidome, GOLPH3 promotes growth factor signaling and cell proliferation, which may explain its oncogenic properties.

G3BPs tether the TSC complex to lysosomes and suppress mTORC1 signaling.

Ras GTPase-activating protein-binding proteins 1 and 2 (G3BP1 and G3BP2, respectively) are widely recognized as core components of stress granules (SGs). We report that G3BPs reside at the cytoplasmic surface of lysosomes. They act in a non-redundant manner to anchor the tuberous sclerosis complex (TSC) protein complex to lysosomes and suppress activation of the metabolic master regulator mechanistic target of rapamycin complex 1 (mTORC1) by amino acids and insulin.

Understanding the role of lipids and lipoproteins in development.

Lipids exert diverse functions in living organisms. They form cellular membranes, store and transport energy and play signalling roles. Some lipid species function in all of these processes, making them ideal candidates to coordinate metabolism with cellular homeostasis and animal development.

Yap/Taz promote the scavenging of extracellular nutrients through macropinocytosis.

The uptake of macromolecules and cellular debris through macropinocytosis has emerged as an important nutrient acquisition strategy of cancer cells. Genetic alterations commonly found in human cancers (e.g.

CDK1 couples proliferation with protein synthesis.

Cell proliferation exerts a high demand on protein synthesis, yet the mechanisms coupling the two processes are not fully understood. A kinase and phosphatase screen for activators of translation, based on the formation of stress granules in human cells, revealed cell cycle-associated kinases as major candidates. CDK1 was identified as a positive regulator of global translation, and cell synchronization experiments showed that this is an extramitotic function of CDK1.

Metabolic functions of macropinocytosis.

Macropinocytosis is an evolutionarily conserved form of endocytosis that mediates non-selective uptake of extracellular fluid and the solutes contained therein. In mammalian cells, macropinocytosis is initiated by growth factor-mediated activation of the Ras and PI3-kinase signalling pathways. In malignant cells, oncogenic activation of growth factor signalling sustains macropinocytosis cell autonomously.

The Canonical Wnt Pathway Drives Macropinocytosis in Cancer.

Macropinocytosis has emerged as an important pathway of protein acquisition in cancer cells, particularly in tumors with activated Ras such as pancreatic and colon cancer. Macropinocytosis is also the route of entry of Bacillus Calmette-Guerin (BCG) and other microbial therapies of cancer. Despite this important role in tumor biology and therapy, the full mechanisms by which cancer cells can activate macropinocytosis remain incompletely defined.

Nutrient acquisition strategies of mammalian cells.

Mammalian cells are surrounded by diverse nutrients, such as glucose, amino acids, various macromolecules and micronutrients, which they can import through transmembrane transporters and endolysosomal pathways. By using different nutrient sources, cells gain metabolic flexibility to survive periods of starvation. Quiescent cells take up sufficient nutrients to sustain homeostasis.

Reexamining How Cancer Cells Exploit the Body's Metabolic Resources.

A key feature of multicellular life is the sharing of nutritional resources by all cells of the organism. In animals, the allocation of nutrients to individual cells is not determined in a cell-autonomous fashion. Instead, growth factor and hormonal signaling pathways have evolved to regulate cellular nutrient uptake, which prevents individual cells from parasitizing the organism's metabolic reserves.

PIKfyve Regulates Vacuole Maturation and Nutrient Recovery following Engulfment.

The scavenging of extracellular macromolecules by engulfment can sustain cell growth in a nutrient-depleted environment. Engulfed macromolecules are contained within vacuoles that are targeted for lysosome fusion to initiate degradation and nutrient export. We have shown that vacuoles containing engulfed material undergo mTORC1-dependent fission that redistributes degraded cargo back into the endosomal network.

NRF2 Promotes Tumor Maintenance by Modulating mRNA Translation in Pancreatic Cancer.

Pancreatic cancer is a deadly malignancy that lacks effective therapeutics. We previously reported that oncogenic Kras induced the redox master regulator Nfe2l2/Nrf2 to stimulate pancreatic and lung cancer initiation. Here, we show that NRF2 is necessary to maintain pancreatic cancer proliferation by regulating mRNA translation.

GCN2 sustains mTORC1 suppression upon amino acid deprivation by inducing Sestrin2.

Mammalian cells possess two amino acid-sensing kinases: general control nonderepressible 2 (GCN2) and mechanistic target of rapamycin complex 1 (mTORC1). Their combined effects orchestrate cellular adaptation to amino acid levels, but how their activities are coordinated remains poorly understood. Here, we demonstrate an important link between GCN2 and mTORC1 signaling.

The Utilization of Extracellular Proteins as Nutrients Is Suppressed by mTORC1.

Despite being surrounded by diverse nutrients, mammalian cells preferentially metabolize glucose and free amino acids. Recently, Ras-induced macropinocytosis of extracellular proteins was shown to reduce a transformed cell's dependence on extracellular glutamine. Here, we demonstrate that protein macropinocytosis can also serve as an essential amino acid source.