ABSTRACT
Adenosine triphosphate-binding cassette transporter subfamily A member 7 (ABCA7) performs incompletely understood biochemical functions that affect pathogenesis of Alzheimer's disease. ABCA7 is most similar in primary structure to ABCA1, the protein that mediates cell lipid efflux and formation of high-density lipoprotein (HDL). Lipid metabolic labeling/tracer efflux assays were employed to investigate lipid efflux in BHK-ABCA7(low expression), BHK-ABCA7(high expression) and BHK-ABCA1 cells. Shotgun lipid mass spectrometry was used to determine lipid composition of HDL synthesized by BHK-ABCA7 and BHK-ABCA1 cells. BHK-ABCA7(low) cells exhibited significant efflux only of choline-phospholipid and phosphatidylinositol. BHK-ABCA7(high) cells had significant cholesterol and choline-phospholipid efflux to apolipoprotein (apo) A-I, apo E, the 18A peptide, HDL, plasma and cerebrospinal fluid and significant efflux of sphingosine-lipid, serine-lipid (which is composed of phosphatidylserine and phosphatidylethanolamine in BHK cells) and phosphatidylinositol to apo A-I. In efflux assays to apo A-I, after adjustment to choline-phospholipid, ABCA7-mediated efflux removed ~4 times more serine-lipid and phosphatidylinositol than ABCA1-mediated efflux, while ABCA1-mediated efflux removed ~3 times more cholesterol than ABCA7-mediated efflux. Shotgun lipidomic analysis revealed that ABCA7-HDL had ~20 mol% less phosphatidylcholine and 3-5 times more serine-lipid and phosphatidylinositol than ABCA1-HDL, while ABCA1-HDL contained only ~6 mol% (or ~1.1 times) more cholesterol than ABCA7-HDL. The discrepancy between the tracer efflux assays and shotgun lipidomics with respect to cholesterol may be explained by an underestimate of ABCA7-mediated cholesterol efflux in the former approach. Overall, these results suggest that ABCA7 lacks specificity for phosphatidylcholine and releases significantly but not dramatically less cholesterol in comparison with ABCA1.
Subject(s)
ATP-Binding Cassette Transporters , Apolipoprotein A-I , ATP-Binding Cassette Transporters/metabolism , Apolipoprotein A-I/metabolism , Cholesterol/metabolism , Choline , Lipoproteins, HDL/metabolism , Phosphatidylcholines/metabolism , Phosphatidylinositols , Phospholipids/metabolism , SerineABSTRACT
During antibody affinity maturation, germinal center (GC) B cells cycle between affinity-driven selection in the light zone (LZ) and proliferation and somatic hypermutation in the dark zone (DZ). Although selection of GC B cells is triggered by antigen-dependent signals delivered in the LZ, DZ proliferation occurs in the absence of such signals. We show that positive selection triggered by T cell help activates the mechanistic target of rapamycin complex 1 (mTORC1), which promotes the anabolic program that supports DZ proliferation. Blocking mTORC1 prior to growth prevented clonal expansion, whereas blockade after cells reached peak size had little to no effect. Conversely, constitutively active mTORC1 led to DZ enrichment but loss of competitiveness and impaired affinity maturation. Thus, mTORC1 activation is required for fueling B cells prior to DZ proliferation rather than for allowing cell-cycle progression itself and must be regulated dynamically during cyclic re-entry to ensure efficient affinity-based selection.
Subject(s)
B-Lymphocytes/physiology , Clonal Selection, Antigen-Mediated , Germinal Center/immunology , Multiprotein Complexes/metabolism , T-Lymphocytes, Helper-Inducer/immunology , TOR Serine-Threonine Kinases/metabolism , Animals , Antibody Affinity , Cell Cycle , Cell Proliferation , Cells, Cultured , Cytokines/metabolism , Mechanistic Target of Rapamycin Complex 1 , Mice , Mice, Inbred C57BL , Mice, Transgenic , Multiprotein Complexes/genetics , Receptors, Antigen, B-Cell/genetics , Sirolimus/pharmacology , Somatic Hypermutation, Immunoglobulin , TOR Serine-Threonine Kinases/geneticsABSTRACT
Extensive reprogramming of cellular energy metabolism is a hallmark of cancer. Despite its importance, the molecular mechanism controlling this tumour metabolic shift remains not fully understood. Here we show that 14-3-3σ regulates cancer metabolic reprogramming and protects cells from tumorigenic transformation. 14-3-3σ opposes tumour-promoting metabolic programmes by enhancing c-Myc poly-ubiquitination and subsequent degradation. 14-3-3σ demonstrates the suppressive impact on cancer glycolysis, glutaminolysis, mitochondrial biogenesis and other major metabolic processes of tumours. Importantly, 14-3-3σ expression levels predict overall and recurrence-free survival rates, tumour glucose uptake and metabolic gene expression in breast cancer patients. Thus, these results highlight that 14-3-3σ is an important regulator of tumour metabolism, and loss of 14-3-3σ expression is critical for cancer metabolic reprogramming. We anticipate that pharmacologically elevating the function of 14-3-3σ in tumours could be a promising direction for targeted anticancer metabolism therapy development in future.
Subject(s)
14-3-3 Proteins/genetics , Biomarkers, Tumor/genetics , Breast Neoplasms/genetics , Energy Metabolism/genetics , Exoribonucleases/genetics , Gene Expression Regulation, Neoplastic , Proto-Oncogene Proteins c-myc/metabolism , 14-3-3 Proteins/metabolism , Adult , Aged , Aged, 80 and over , Biomarkers, Tumor/metabolism , Breast Neoplasms/metabolism , Cell Line, Tumor , Disease-Free Survival , Exoribonucleases/metabolism , Female , Gene Knockout Techniques , Glutamine/metabolism , Glycolysis/genetics , HCT116 Cells , Humans , Middle Aged , Organelle Biogenesis , Prognosis , Proteolysis , Ubiquitination/genetics , Young AdultABSTRACT
Everolimus, an inhibitor of the mammalian target of rapamycin (mTOR), is effective in treating tumors harboring alterations in the mTOR pathway. Mechanisms of resistance to everolimus remain undefined. Resistance developed in a patient with metastatic anaplastic thyroid carcinoma after an extraordinary 18-month response. Whole-exome sequencing of pretreatment and drug-resistant tumors revealed a nonsense mutation in TSC2, a negative regulator of mTOR, suggesting a mechanism for exquisite sensitivity to everolimus. The resistant tumor also harbored a mutation in MTOR that confers resistance to allosteric mTOR inhibition. The mutation remains sensitive to mTOR kinase inhibitors.
Subject(s)
Antineoplastic Agents/therapeutic use , Drug Resistance, Neoplasm/genetics , Sirolimus/analogs & derivatives , TOR Serine-Threonine Kinases/genetics , Thyroid Neoplasms/therapy , Tumor Suppressor Proteins/genetics , Combined Modality Therapy , Everolimus , Female , Humans , Lymphatic Metastasis/pathology , Middle Aged , Mutation , Neoplasm Recurrence, Local/diagnostic imaging , Neoplasm Recurrence, Local/pathology , Protein Conformation , Radiography , Sirolimus/therapeutic use , TOR Serine-Threonine Kinases/chemistry , Thyroid Carcinoma, Anaplastic , Thyroid Neoplasms/diagnostic imaging , Thyroid Neoplasms/genetics , Thyroid Neoplasms/pathology , Tuberous Sclerosis Complex 2 ProteinABSTRACT
Understanding the genetic mechanisms of sensitivity to targeted anticancer therapies may improve patient selection, response to therapy, and rational treatment designs. One approach to increase this understanding involves detailed studies of exceptional responders: rare patients with unexpected exquisite sensitivity or durable responses to therapy. We identified an exceptional responder in a phase I study of pazopanib and everolimus in advanced solid tumors. Whole-exome sequencing of a patient with a 14-month complete response on this trial revealed two concurrent mutations in mTOR, the target of everolimus. In vitro experiments demonstrate that both mutations are activating, suggesting a biologic mechanism for exquisite sensitivity to everolimus in this patient. The use of precision (or "personalized") medicine approaches to screen patients with cancer for alterations in the mTOR pathway may help to identify subsets of patients who may benefit from targeted therapies directed against mTOR.
Subject(s)
Antineoplastic Agents/administration & dosage , Antineoplastic Combined Chemotherapy Protocols/administration & dosage , Carcinoma, Transitional Cell/drug therapy , Everolimus/administration & dosage , Pyrimidines/administration & dosage , Sulfonamides/administration & dosage , TOR Serine-Threonine Kinases/genetics , Urinary Bladder Neoplasms/drug therapy , Aged , Antineoplastic Agents/pharmacokinetics , Antineoplastic Agents/therapeutic use , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Carcinoma, Transitional Cell/genetics , Drug Administration Schedule , Everolimus/pharmacokinetics , Everolimus/therapeutic use , Female , High-Throughput Nucleotide Sequencing , Humans , Indazoles , Lymphatic Metastasis/diagnostic imaging , Lymphatic Metastasis/genetics , Male , Middle Aged , Mutation , Precision Medicine , Pyrimidines/pharmacokinetics , Pyrimidines/therapeutic use , Radionuclide Imaging , Sequence Analysis, DNA , Sulfonamides/pharmacokinetics , Sulfonamides/therapeutic use , TOR Serine-Threonine Kinases/antagonists & inhibitors , TOR Serine-Threonine Kinases/chemistry , Urinary Bladder Neoplasms/geneticsABSTRACT
Genes encoding components of the PI3K-AKT-mTOR signaling axis are frequently mutated in cancer, but few mutations have been characterized in MTOR, the gene encoding the mTOR kinase. Using publicly available tumor genome sequencing data, we generated a comprehensive catalog of mTOR pathway mutations in cancer, identifying 33 MTOR mutations that confer pathway hyperactivation. The mutations cluster in six distinct regions in the C-terminal half of mTOR and occur in multiple cancer types, with one cluster particularly prominent in kidney cancer. The activating mutations do not affect mTOR complex assembly, but a subset reduces binding to the mTOR inhibitor DEPTOR. mTOR complex 1 (mTORC1) signaling in cells expressing various activating mutations remains sensitive to pharmacologic mTOR inhibition, but is partially resistant to nutrient deprivation. Finally, cancer cell lines with hyperactivating MTOR mutations display heightened sensitivity to rapamycin both in culture and in vivo xenografts, suggesting that such mutations confer mTOR pathway dependency.
Subject(s)
Antibiotics, Antineoplastic/pharmacology , Mutation , Neoplasms/drug therapy , Sirolimus/pharmacology , TOR Serine-Threonine Kinases/genetics , Animals , Antibiotics, Antineoplastic/administration & dosage , Cell Line, Tumor , Databases, Factual , HEK293 Cells , HeLa Cells , Humans , MAP Kinase Signaling System/drug effects , MCF-7 Cells , Mechanistic Target of Rapamycin Complex 1 , Mechanistic Target of Rapamycin Complex 2 , Mice , Mice, Nude , Multiprotein Complexes/metabolism , Neoplasms/genetics , Neoplasms, Experimental , Protein Kinase Inhibitors/administration & dosage , Protein Kinase Inhibitors/pharmacology , Sirolimus/administration & dosage , TOR Serine-Threonine Kinases/antagonists & inhibitors , TOR Serine-Threonine Kinases/metabolism , Xenograft Model Antitumor AssaysABSTRACT
The mTOR complex 1 (mTORC1) pathway promotes cell growth in response to many cues, including amino acids, which act through the Rag guanosine triphosphatases (GTPases) to promote mTORC1 translocation to the lysosomal surface, its site of activation. Although progress has been made in identifying positive regulators of the Rags, it is unknown if negative factors also exist. Here, we identify GATOR as a complex that interacts with the Rags and is composed of two subcomplexes we call GATOR1 and -2. Inhibition of GATOR1 subunits (DEPDC5, Nprl2, and Nprl3) makes mTORC1 signaling resistant to amino acid deprivation. In contrast, inhibition of GATOR2 subunits (Mios, WDR24, WDR59, Seh1L, and Sec13) suppresses mTORC1 signaling, and epistasis analysis shows that GATOR2 negatively regulates DEPDC5. GATOR1 has GTPase-activating protein (GAP) activity for RagA and RagB, and its components are mutated in human cancer. In cancer cells with inactivating mutations in GATOR1, mTORC1 is hyperactive and insensitive to amino acid starvation, and such cells are hypersensitive to rapamycin, an mTORC1 inhibitor. Thus, we identify a key negative regulator of the Rag GTPases and reveal that, like other mTORC1 regulators, Rag function can be deregulated in cancer.
Subject(s)
Amino Acids/metabolism , Carrier Proteins/metabolism , Lysosomes/enzymology , Monomeric GTP-Binding Proteins/metabolism , Neoplasms/enzymology , Proteins/metabolism , Tumor Suppressor Proteins/metabolism , Carrier Proteins/antagonists & inhibitors , Carrier Proteins/genetics , Cell Line, Tumor , GTPase-Activating Proteins , HEK293 Cells , Humans , Mechanistic Target of Rapamycin Complex 1 , Multiprotein Complexes , Mutation , Neoplasms/genetics , Nuclear Proteins/antagonists & inhibitors , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , RNA, Small Interfering/genetics , TOR Serine-Threonine Kinases , Tumor Suppressor Proteins/antagonists & inhibitors , Tumor Suppressor Proteins/geneticsABSTRACT
EGF activates NF-κB, and constitutively activated NF-κB contributes to EGFR mutation-associated tumorigenesis, but it remains unclear precisely how EGFR signaling leads to NF-κB activation. Here we report that CARMA3, a caspase recruitment domain (CARD)-containing scaffold molecule, is required for EGF-induced NF-κB activation. CARMA3 deficiency impaired the activation of the IKK complex following EGF stimulation, resulting in a defect of EGF-induced IκBα phosphorylation and NF-κB activation. We found that CARMA3 and Bcl10 contributed to several characteristics of EGFR-associated malignancy, including proliferation, survival, migration, and invasion. Most importantly, CARMA3 contributed to tumor growth in vivo. Our findings elucidate a crucial link between EGFR-proximal signaling components and the downstream IKK complex, and they suggest a new therapeutic target for treatment of EGFR-driven cancers.
Subject(s)
Breast Neoplasms/metabolism , CARD Signaling Adaptor Proteins/metabolism , ErbB Receptors/metabolism , NF-kappa B/metabolism , Adaptor Proteins, Signal Transducing/genetics , Adaptor Proteins, Signal Transducing/metabolism , Animals , B-Cell CLL-Lymphoma 10 Protein , Breast Neoplasms/genetics , Breast Neoplasms/pathology , CARD Signaling Adaptor Proteins/genetics , Cell Cycle , Cell Line, Tumor , Cell Movement , Cell Proliferation , Cell Survival , Epidermal Growth Factor/pharmacology , ErbB Receptors/genetics , Female , Fibroblasts/cytology , Fibroblasts/drug effects , Fibroblasts/metabolism , Humans , I-kappa B Proteins/metabolism , Male , Mammary Neoplasms, Experimental/genetics , Mammary Neoplasms, Experimental/metabolism , Mammary Neoplasms, Experimental/pathology , Mice , Mice, Inbred BALB C , Mice, Knockout , Mice, Nude , NF-KappaB Inhibitor alpha , RNA Interference , Transplantation, Heterologous , Tumor BurdenABSTRACT
Akt signaling plays a central role in many biological functions, such as cell proliferation and apoptosis. Because Akt (also known as protein kinase B) resides primarily in the cytosol, it is not known how these signaling molecules are recruited to the plasma membrane and subsequently activated by growth factor stimuli. We found that the protein kinase Akt undergoes lysine-63 chain ubiquitination, which is important for Akt membrane localization and phosphorylation. TRAF6 was found to be a direct E3 ligase for Akt and was essential for Akt ubiquitination, membrane recruitment, and phosphorylation upon growth-factor stimulation. The human cancer-associated Akt mutant displayed an increase in Akt ubiquitination, in turn contributing to the enhancement of Akt membrane localization and phosphorylation. Thus, Akt ubiquitination is an important step for oncogenic Akt activation.
Subject(s)
Cell Membrane/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Signal Transduction , TNF Receptor-Associated Factor 6/metabolism , Ubiquitin-Protein Ligases/metabolism , Amino Acid Motifs , Animals , Apoptosis , Cell Line , Cell Line, Tumor , Humans , Insulin-Like Growth Factor I/pharmacology , Interleukin-1beta/pharmacology , Lipopolysaccharides/pharmacology , Mice , Neoplasm Transplantation , Neoplasms, Experimental/metabolism , Phosphatidylinositol Phosphates/metabolism , Phosphorylation , Proto-Oncogene Proteins c-akt/chemistry , TNF Receptor-Associated Factor 6/genetics , Transplantation, Heterologous , UbiquitinationABSTRACT
Lysophosphatidic acid (LPA) is a potent agonist that exerts various cellular functions on many cell types through binding to its cognate G protein-coupled receptors (GPCRs). Although LPA induces NF-kappaB activation by acting on its GPCR receptor, the molecular mechanism of LPA receptor-mediated NF-kappaB activation remains to be well defined. In the present study, by using MEKK3-, TAK1-, and IKKbeta-deficient murine embryonic fibroblasts (MEFs), we found that MEKK3 but not TAK1 deficiency impairs LPA and protein kinase C (PKC)-induced IkappaB kinase (IKK)-NF-kappaB activation, and IKKbeta is required for PKC-induced NF-kappaB activation. In addition, we demonstrate that LPA and PKC-induced IL-6 and MIP-2 production are abolished in the absence of MEKK3 but not TAK1. Together, our results provide the genetic evidence that MEKK3 but not TAK1 is required for LPA receptor-mediated IKK-NF-kappaB activation.
Subject(s)
Lysophospholipids/pharmacology , MAP Kinase Kinase Kinase 3/metabolism , NF-kappa B/metabolism , Animals , Chemokine CXCL2/metabolism , Fibroblasts/enzymology , Fibroblasts/metabolism , Gene Knockdown Techniques , I-kappa B Kinase/deficiency , I-kappa B Kinase/genetics , I-kappa B Kinase/metabolism , Interleukin-6/metabolism , MAP Kinase Kinase Kinase 3/deficiency , MAP Kinase Kinase Kinase 3/genetics , MAP Kinase Kinase Kinases/deficiency , MAP Kinase Kinase Kinases/genetics , MAP Kinase Kinase Kinases/metabolism , Mice , Protein Kinase C/metabolism , Receptors, G-Protein-Coupled/genetics , Receptors, G-Protein-Coupled/metabolism , Signal TransductionABSTRACT
G protein-coupled receptors (GPCRs) play pivotal roles in regulating various cellular functions. Although many GPCRs induce NF-kappaB activation, the molecular mechanism of GPCR-induced NF-kappaB activation remains largely unknown. CARMA3 (CARD and MAGUK domain-containing protein 3) is a scaffold molecule with unknown biological functions. By generating CARMA3 knockout mice using the gene targeting approach, here we show CARMA3 is required for GPCR-induced NF-kappaB activation. Mechanistically, we found that CARMA3 deficiency impairs GPCR-induced IkappaB kinase (IKK) activation, although it does not affect GPCR-induced IKKalpha/beta phosphorylation, indicating that inducible phosphorylation of IKKalpha/beta alone is not sufficient to induce its kinase activity. We also found that CARMA3 is physically associated with NEMO/IKKgamma, and induces polyubiquitination of an unknown protein(s) that associates with NEMO, likely by linking NEMO to TRAF6. Consistently, we found TRAF6 deficiency also abrogates GPCR-induced NF-kappaB activation. Together, our results provide the genetic evidence that CARMA3 is required for GPCR-induced NF-kappaB activation.
Subject(s)
Apoptosis Regulatory Proteins/metabolism , CARD Signaling Adaptor Proteins/metabolism , NF-kappa B/metabolism , Receptors, G-Protein-Coupled/metabolism , Adaptor Proteins, Signal Transducing/metabolism , Animals , Apoptosis Regulatory Proteins/genetics , B-Cell CLL-Lymphoma 10 Protein , CARD Signaling Adaptor Proteins/genetics , Embryo, Mammalian/cytology , Female , Fibroblasts , I-kappa B Kinase/metabolism , Lysophospholipids/metabolism , Mice , Mice, Knockout , Phosphorylation , Pregnancy , Signal Transduction , TNF Receptor-Associated Factor 6/metabolismABSTRACT
Type I insulin-like growth factor receptor (IGF-IR) can transform mouse fibroblasts; however, little is known about the transforming potential of IGF-IR in human fibroblasts or epithelial cells. We found that overexpression of a constitutively activated IGF-IR (CD8-IGF-IR) was sufficient to cause transformation of immortalized human mammary epithelial cells and growth in immunocompromised mice. Furthermore, CD8-IGF-IR caused cells to undergo an epithelial-to-mesenchymal transition (EMT) which was associated with dramatically increased migration and invasion. The EMT was mediated by the induction of the transcriptional repressor Snail and downregulation of E-cadherin. NF-kappaB was highly active in CD8-IGF-IR-MCF10A cells, and both increased levels of Snail and the EMT were partially reversed by blocking NF-kappaB or IGF-IR activity. This study places IGF-IR among a small group of oncogenes that, when overexpressed alone, can confer in vivo tumorigenic growth of MCF10A cells and indicates the hierarchy in the mechanism of IGF-IR-induced EMT.
Subject(s)
Cell Transformation, Neoplastic , Epithelial Cells/cytology , Mammary Glands, Human/cytology , Mesoderm/cytology , NF-kappa B/metabolism , Receptor, IGF Type 1/metabolism , Transcription Factors/metabolism , Animals , Benzimidazoles/pharmacology , CD8 Antigens/metabolism , Cadherins/genetics , Cell Transformation, Neoplastic/drug effects , Collagen/drug effects , Down-Regulation/drug effects , Drug Combinations , Epithelial Cells/drug effects , Genes, Regulator , Humans , Laminin/drug effects , Mammary Glands, Human/drug effects , Mammary Glands, Human/growth & development , Mice , Models, Biological , Morphogenesis/drug effects , Proteoglycans/drug effects , Pyridones/pharmacology , Receptor, IGF Type 1/antagonists & inhibitors , Recombinant Fusion Proteins/metabolism , Snail Family Transcription Factors , Transplantation, HeterologousABSTRACT
The Ets family members Spi-1 and Spi-B have been implicated in the regulation of genes important for B cell antigen receptor (BCR) signaling. Mice deficient in Spi-B exhibit reduced B cell proliferation in response to BCR cross-linking and impaired T cell-dependent immune responses. This defect is exacerbated in the presence of Spi-1 haplo-insufficiency (Spi1+/- SpiB-/-). Tyrosine phosphorylation and calcium mobilization induced by BCR engagement is diminished in Spi1+/- SpiB-/- B lymphocytes, although many key BCR signaling proteins are expressed, suggesting that Spi-1 and Spi-B regulate expression of additional, unidentified signaling molecules. We now demonstrate that expression of the adaptor protein Grap2 is impaired in Spi1+/- SpiB+/- and Spi1+/- SpiB-/- B lymphocytes. Analysis of two alternate murine Grap2 promoters revealed a functionally important Spi-1 and Spi-B DNA binding element located in the downstream promoter. Ectopic expression of Grap2 in Grap2-deficient B cells reduced the recruitment of BLNK to Igalpha and the phosphorylation of specific substrates. Regulation of BLNK recruitment was dependent upon the Grap2 proline-rich domain, while modulation of phosphorylation was dependent upon both the proline-rich and SH2 domains. These data indicate that Spi-1 and Spi-B directly regulate the expression of Grap2 and that Grap2 functions to modulate BCR signaling, but that reduced Grap2 expression is unlikely to account for the BCR signaling defects observed in Spi1+/- SpiB-/- B cells.