UBA6 and NDFIP1 regulate the degradation of ferroportin

Hepcidin regulates iron homeostasis by controlling the level of ferroportin, the only membrane channel that facilitates export of iron from within cells. Binding of hepcidin to ferroportin induces the ubiquitination of ferroportin at multiple lysine residues and subsequently causes the internalization and degradation of the ligand-channel complex within lysosomes. The objective of this study was to identify components of the ubiquitin system that are involved in ferroportin degradation. A HepG2 cell line, which inducibly expresses ferroportin-GFP (FPN-GFP), was established to test the ability of siRNAs directed against components of the ubiquitin system to prevent BMP6- and exogenous hepcidin-induced ferroportin degradation. Of the 88 siRNAs directed against components of the ubiquitin pathway that were tested, siRNAmediated depletion of the alternative E1 enzyme UBA6 as well as the adaptor protein NDFIP1 prevented BMP6- and hepcidin- induced degradation of ferroportin in vitro. A third component of the ubiquitin pathway, ARIH1, indirectly inhibited ferroportin degradation by impairing BMP6 mediated induction of hepcidin. In mice, the AAVmediated silencing of Ndfip1 in the murine liver increased the level of hepatic ferroportin and increased circulating iron. The results suggest that the E1 enzyme UBA6 and the adaptor protein NDFIP1 are involved in iron homeostasis by regulating the degradation of ferroportin. These specific components of the ubiquitin system may be promising targets for the treatment of iron related diseases, including iron overload and anemia of inflammation.

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The E3 Ubiquitin Ligase TBK1 Mediates the Degradation of Multiple Picornavirus VP3 Proteins by Phosphorylation and Ubiquitination

Journal of Virology ◽

10.1128/jvi.01438-19 ◽

2019 ◽

Vol 93 (23) ◽

Cited By ~ 4

Author(s):

Dan Li ◽

Wenping Yang ◽

Jingjing Ren ◽

Yi Ru ◽

Keshan Zhang ◽

...

Keyword(s):

Ubiquitin Ligase ◽

Molecular Mechanisms ◽

E3 Ubiquitin Ligase ◽

Adaptor Protein ◽

Ubiquitin Ligase Activity ◽

Lysine Residues ◽

Innate Antiviral Immunity

ABSTRACT TANK-binding kinase 1 (TBK1) is essential for interferon beta (IFN-β) production and innate antiviral immunity. However, other, additional functions of TBK1 have remained elusive. Here, we showed that TBK1 is an E3 ubiquitin ligase that undergoes self-ubiquitylation in vitro in the presence of the E2 enzyme UbcH5c. Further evidence showed that TBK1 could also be self-ubiquitylated in vivo. Importantly, multiple picornavirus VP3 proteins were degraded by TBK1 through its kinase and E3 ubiquitin ligase activity. Mechanistically, TBK1 phosphorylated multiple picornavirus VP3 proteins at serine residues and ubiquitinated them via K63-linked ubiquitination at lysine residues. In addition, the C426 and C605 residues of TBK1 were not essential for TBK1 innate immunity activity; however, these residues were required for degradation of multiple picornavirus VP3 proteins and for its E3 ubiquitin ligase activity. Hence, our findings identified a novel role of TBK1 in regulating the virus life cycle and provided new insights into the molecular mechanisms of TBK1-mediated antiviral response. IMPORTANCE TBK1 is an important adaptor protein required for innate immune response to viruses, but its other functions were unknown. In this study, we found that TBK1 is an E3 ubiquitin ligase that undergoes self-ubiquitylation in vitro in the presence of the E2 enzyme UbcH5c. In addition, multiple picornavirus VP3 proteins were degraded by TBK1 through its kinase and E3 ubiquitin ligase activity. Our report provides evidence that TBK1 plays a role in viral protein degradation.

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Loss of ferroportin induces memory impairment by promoting ferroptosis in Alzheimer’s disease

Cell Death and Differentiation ◽

10.1038/s41418-020-00685-9 ◽

2021 ◽

Author(s):

Wen-Dai Bao ◽

Pei Pang ◽

Xiao-Ting Zhou ◽

Fan Hu ◽

Wan Xiong ◽

...

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Memory Impairment ◽

Iron Homeostasis ◽

Critical Role ◽

Gene Set Enrichment Analysis ◽

Molecular Characteristics ◽

Intracellular Iron

AbstractIron homeostasis disturbance has been implicated in Alzheimer’s disease (AD), and excess iron exacerbates oxidative damage and cognitive defects. Ferroptosis is a nonapoptotic form of cell death dependent upon intracellular iron. However, the involvement of ferroptosis in the pathogenesis of AD remains elusive. Here, we report that ferroportin1 (Fpn), the only identified mammalian nonheme iron exporter, was downregulated in the brains of APPswe/PS1dE9 mice as an Alzheimer’s mouse model and Alzheimer’s patients. Genetic deletion of Fpn in principal neurons of the neocortex and hippocampus by breeding Fpnfl/fl mice with NEX-Cre mice led to AD-like hippocampal atrophy and memory deficits. Interestingly, the canonical morphological and molecular characteristics of ferroptosis were observed in both Fpnfl/fl/NEXcre and AD mice. Gene set enrichment analysis (GSEA) of ferroptosis-related RNA-seq data showed that the differentially expressed genes were highly enriched in gene sets associated with AD. Furthermore, administration of specific inhibitors of ferroptosis effectively reduced the neuronal death and memory impairments induced by Aβ aggregation in vitro and in vivo. In addition, restoring Fpn ameliorated ferroptosis and memory impairment in APPswe/PS1dE9 mice. Our study demonstrates the critical role of Fpn and ferroptosis in the progression of AD, thus provides promising therapeutic approaches for this disease.

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Lysine acetyltransferase Tip60 acetylates the APP adaptor Fe65 to increase its transcriptional activity

Biological Chemistry ◽

10.1515/hsz-2020-0279 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Sabine Probst ◽

Florian Riese ◽

Larissa Kägi ◽

Maik Krüger ◽

Natalie Russi ◽

...

Keyword(s):

Transcriptional Activity ◽

Target Genes ◽

Adaptor Protein ◽

Proteolytic Processing ◽

Class Iii ◽

Lysine Deacetylase ◽

Lysine Residues ◽

Lysine Acetyltransferase ◽

Complex Forms ◽

Spot Formation

AbstractProteolytic processing of the amyloid precursor protein (APP) releases the APP intracellular domain (AICD) from the membrane. Bound to the APP adaptor protein Fe65 and the lysine acetyltransferase (KAT) Tip60, AICD translocates to the nucleus. Here, the complex forms spherical condensates at sites of endogenous target genes, termed AFT spots (AICD-Fe65-Tip60). We show that loss of Tip60 KAT activity prevents autoacetylation, reduces binding of Fe65 and abolishes Fe65-mediated stabilization of Tip60. Autoacetylation is a prerequisite for AFT spot formation, with KAT-deficient Tip60 retained together with Fe65 in speckles. We identify lysine residues 204 and 701 of Fe65 as acetylation targets of Tip60. We do not detect acetylation of AICD. Mutation of Fe65 K204 and K701 to glutamine, mimicking acetylation-induced charge neutralization, increases the transcriptional activity of Fe65 whereas Tip60 inhibition reduces it. The lysine deacetylase (KDAC) class III Sirt1 deacetylates Fe65 and pharmacological modulation of Sirt1 activity regulates Fe65 transcriptional activity. A second acetylation/deacetylation cycle, conducted by CBP and class I/II KDACs at different lysine residues, regulates stability of Fe65. This is the first report describing a role for acetylation in the regulation of Fe65 transcriptional activity, with Tip60 being the only KAT tested that supports AFT spot formation.

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Lipopolysaccharide induces neuroinflammation in microglia by activating the MTOR pathway and downregulating Vps34 to inhibit autophagosome formation

Journal of Neuroinflammation ◽

10.1186/s12974-019-1644-8 ◽

2020 ◽

Vol 17 (1) ◽

Cited By ~ 8

Author(s):

Xiaoxia Ye ◽

Mingming Zhu ◽

Xiaohang Che ◽

Huiyang Wang ◽

Xing-Jie Liang ◽

...

Keyword(s):

Inflammatory Response ◽

Microglial Activation ◽

Adaptor Protein ◽

Mtor Pathway ◽

Microglial Cells ◽

Inflammatory Factors ◽

Intraventricular Injection ◽

Enzyme Linked Immunosorbent Assay ◽

Autophagic Flux

Abstract Background Microglial activation is a prominent feature of neuroinflammation, which is present in almost all neurodegenerative diseases. While an initial inflammatory response mediated by microglia is considered to be protective, excessive pro-inflammatory response of microglia contributes to the pathogenesis of neurodegeneration. Although autophagy is involved in the suppression of inflammation, its role and mechanism in microglia are unclear. Methods In the present study, we studied the mechanism by which lipopolysaccharide (LPS) affects microglial autophagy and the effects of autophagy on the production of pro-inflammatory factors in microglial cells by western blotting, immunocytochemistry, transfection, transmission electron microscopy (TEM), and real-time PCR. In a mouse model of neuroinflammation, generated by intraventricular injection of LPS (5 μg/animal), we induced autophagy by rapamycin injection and investigated the effects of enhanced autophagy on microglial activation by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry. Results We found that autophagic flux was suppressed in LPS-stimulated N9 microglial cells, as evidenced by decreased expression of the autophagy marker LC3-II (lipidated form of MAP1LC3), as well as increased levels of the autophagy adaptor protein SQSTM1. LPS significantly decreased Vps34 expression in N9 microglial cells by activating the PI3KI/AKT/MTOR pathway without affecting the levels of lysosome-associated proteins and enzymes. More importantly, overexpression of Vps34 significantly enhanced the autophagic flux and decreased the accumulation of SQSTM1 in LPS-stimulated N9 microglial cells. Moreover, our results revealed that an LPS-induced reduction in the level of Vps34 prevented the maturation of omegasomes to phagophores. Furthermore, LPS-induced neuroinflammation was significantly ameliorated by treatment with the autophagy inducer rapamycin both in vitro and in vivo. Conclusions These data reveal that LPS-induced neuroinflammation in N9 microglial cells is associated with the inhibition of autophagic flux through the activation of the PI3KI/AKT/MTOR pathway, while enhanced microglial autophagy downregulates LPS-induced neuroinflammation. Thus, this study suggests that promoting the early stages of autophagy might be a potential therapeutic approach for neuroinflammation-associated diseases.

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Lysyl oxidase activity and elastin/glycosaminoglycan interactions in growing chick and rat aortas.

The Journal of Cell Biology ◽

10.1083/jcb.105.3.1463 ◽

1987 ◽

Vol 105 (3) ◽

pp. 1463-1469 ◽

Cited By ~ 60

Author(s):

C Fornieri ◽

M Baccarani-Contri ◽

D Quaglino ◽

I Pasquali-Ronchetti

Keyword(s):

Hydrophobic Interactions ◽

Isonicotinic Acid ◽

Lysyl Oxidase ◽

Acid Hydrazide ◽

Elastic Fibers ◽

Amino Groups ◽

Lysine Residues ◽

Oxidase Inhibition

Hydrophobic tropoelastin molecules aggregate in vitro in physiological conditions and form fibers very similar to natural ones (Bressan, G. M., I. Pasquali Ronchetti, C. Fornieri, F. Mattioli, I. Castellani, and D. Volpin, 1986, J. Ultrastruct. Molec. Struct. Res., 94:209-216). Similar hydrophobic interactions might be operative in in vivo fibrogenesis. Data are presented suggesting that matrix glycosaminoglycans (GAGs) prevent spontaneous tropoelastin aggregation in vivo, at least up to the deamination of lysine residues on tropoelastin by matrix lysyl oxidase. Lysyl oxidase inhibitors beta-aminopropionitrile, aminoacetonitrile, semicarbazide, and isonicotinic acid hydrazide were given to newborn chicks, to chick embryos, and to newborn rats, and the ultrastructural alterations of the aortic elastic fibers were analyzed and compared with the extent of the enzyme inhibition. When inhibition was greater than 65% all chemicals induced alterations of elastic fibers in the form of lateral aggregates of elastin, which were always permeated by cytochemically and immunologically recognizable GAGs. The number and size of the abnormal elastin/GAGs aggregates were proportional to the extent of lysyl oxidase inhibition. The phenomenon was independent of the animal species. All data suggest that, upon inhibition of lysyl oxidase, matrix GAGs remain among elastin molecules during fibrogenesis by binding to positively charged amino groups on elastin. Newly synthesized and secreted tropoelastin has the highest number of free epsilon amino groups, and, therefore, the highest capability of binding to GAGs. These polyanions, by virtue of their great hydration and dispersing power, could prevent random spontaneous aggregation of hydrophobic tropoelastin in the extracellular space.

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Absence of the Adaptor Protein PEA-15 Is Associated with Altered Pattern of Th Cytokines Production by Activated CD4+ T Lymphocytes In Vitro, and Defective Red Blood Cell Alloimmune Response In Vivo

PLoS ONE ◽

10.1371/journal.pone.0136885 ◽

2015 ◽

Vol 10 (8) ◽

pp. e0136885 ◽

Cited By ~ 6

Author(s):

Stéphane Kerbrat ◽

Benoit Vingert ◽

Marie-Pierre Junier ◽

Flavia Castellano ◽

François Renault-Mihara ◽

...

Keyword(s):

T Lymphocytes ◽

Blood Cell ◽

Red Blood Cell ◽

Adaptor Protein

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A Novel Human Ada2 Homologue Functions with Gcn5 or Brg1 To Coactivate Transcription

Molecular and Cellular Biology ◽

10.1128/mcb.23.19.6944-6957.2003 ◽

2003 ◽

Vol 23 (19) ◽

pp. 6944-6957 ◽

Cited By ~ 46

Author(s):

Nickolai A. Barlev ◽

Alexander V. Emelyanov ◽

Paola Castagnino ◽

Philip Zegerman ◽

Andrew J. Bannister ◽

...

Keyword(s):

Histone Acetylation ◽

Chromatin Remodeling ◽

Adaptor Protein ◽

Saga Complex ◽

Yeast Two Hybrid ◽

Functional Assays ◽

Two Hybrid ◽

Histone Acetyltransferase Activity

ABSTRACT In yeast, the transcriptional adaptor yeast Ada2 (yAda2) is a part of the multicomponent SAGA complex, which possesses histone acetyltransferase activity through action of the yGcn5 catalytic enzyme. yAda2, among several SAGA proteins, serves to recruit SAGA to genes via interactions with promoter-bound transcription factors. Here we report identification of a new human Ada2 homologue, hAda2β. Ada2β differs both biochemically and functionally from the previously characterized hAda2α, which is a stable component of the human PCAF (human Gcn5 homologue) acetylase complex. Ada2β, relative to Ada2α, interacted selectively, although not stably, with the Gcn5-containing histone acetylation complex TFTC/STAGA. In addition, Ada2β interacted with Baf57 (a component of the human Swi/Snf complex) in a yeast two-hybrid screen and associated with human Swi/Snf in vitro. In functional assays, hAda2β (but not Ada2α), working in concert with Gcn5 (but not PCAF) or Brg1 (the catalytic component of hSwi/Snf complex), increased transcription via the B-cell-specific transcription factor Pax5/BSAP. These findings support the view that Gcn5 and PCAF have distinct roles in vivo and suggest a new mechanism of coactivator function, in which a single adaptor protein (Ada2β) can coordinate targeting of both histone acetylation and chromatin remodeling activities.

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The Ubiquitously Expressed Csk Adaptor Protein Cbp Is Dispensable for Embryogenesis and T-Cell Development and Function

Molecular and Cellular Biology ◽

10.1128/mcb.25.23.10533-10542.2005 ◽

2005 ◽

Vol 25 (23) ◽

pp. 10533-10542 ◽

Cited By ~ 59

Author(s):

Marc-Werner Dobenecker ◽

Christian Schmedt ◽

Masato Okada ◽

Alexander Tarakhovsky

Keyword(s):

T Cell ◽

Adaptor Protein ◽

Regulatory Function ◽

Loss Of Function ◽

Thymic Development ◽

Cell Functions ◽

Carboxy Terminal ◽

And Function

ABSTRACT Regulation of Src family kinase (SFK) activity is indispensable for a functional immune system and embryogenesis. The activity of SFKs is inhibited by the presence of the carboxy-terminal Src kinase (Csk) at the cell membrane. Thus, recruitment of cytosolic Csk to the membrane-associated SFKs is crucial for its regulatory function. Previous studies utilizing in vitro and transgenic models suggested that the Csk-binding protein (Cbp), also known as phosphoprotein associated with glycosphingolipid microdomains (PAG), is the membrane adaptor for Csk. However, loss-of-function genetic evidence to support this notion was lacking. Herein, we demonstrate that the targeted disruption of the cbp gene in mice has no effect on embryogenesis, thymic development, or T-cell functions in vivo. Moreover, recruitment of Csk to the specialized membrane compartment of “lipid rafts” is not impaired by Cbp deficiency. Our results indicate that Cbp is dispensable for the recruitment of Csk to the membrane and that another Csk adaptor, yet to be discovered, compensates for the loss of Cbp.

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Expression level and differential JAK2-V617F–binding of the adaptor protein Lnk regulates JAK2-mediated signals in myeloproliferative neoplasms

Blood ◽

10.1182/blood-2009-12-256768 ◽

2010 ◽

Vol 116 (26) ◽

pp. 5961-5971 ◽

Cited By ~ 33

Author(s):

Fanny Baran-Marszak ◽

Hajer Magdoud ◽

Christophe Desterke ◽

Anabell Alvarado ◽

Claudine Roger ◽

...

Keyword(s):

Myeloproliferative Neoplasms ◽

Adaptor Protein ◽

Jak2 V617f ◽

Negative Control ◽

Sh2 Domain ◽

Expression Level ◽

Activating Mutations ◽

Thrombopoietin Receptor ◽

Dependent Cell

Abstract Activating mutations in signaling molecules, such as JAK2-V617F, have been associated with myeloproliferative neoplasms (MPNs). Mice lacking the inhibitory adaptor protein Lnk display deregulation of thrombopoietin/thrombopoietin receptor signaling pathways and exhibit similar myeloproliferative characteristics to those found in MPN patients, suggesting a role for Lnk in the molecular pathogenesis of these diseases. Here, we showed that LNK levels are up-regulated and correlate with an increase in the JAK2-V617F mutant allele burden in MPN patients. Using megakaryocytic cells, we demonstrated that Lnk expression is regulated by the TPO-signaling pathway, thus indicating an important negative control loop in these cells. Analysis of platelets derived from MPN patients and megakaryocytic cell lines showed that Lnk can interact with JAK2-WT and V617F through its SH2 domain, but also through an unrevealed JAK2-binding site within its N-terminal region. In addition, the presence of the V617F mutation causes a tighter association with Lnk. Finally, we found that the expression level of the Lnk protein can modulate JAK2-V617F–dependent cell proliferation and that its different domains contribute to the inhibition of multilineage and megakaryocytic progenitor cell growth in vitro. Together, our results indicate that changes in Lnk expression and JAK2-V617F–binding regulate JAK2-mediated signals in MPNs.

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5HT1A Serotonin Receptor Agonists Inhibit Plasmodium falciparum by Blocking a Membrane Channel

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.47.12.3806-3809.2003 ◽

2003 ◽

Vol 47 (12) ◽

pp. 3806-3809 ◽

Cited By ~ 8

Author(s):

Christopher P. Locher ◽

Peter C. Ruben ◽

Jiri Gut ◽

Philip J. Rosenthal

Keyword(s):

Serotonin Receptor ◽

Surface Membrane ◽

Resistant Isolate ◽

Neurological Involvement ◽

Membrane Channel ◽

Transport Pathway ◽

Human Lung Fibroblast ◽

Receptor Agonists ◽

Serotonin Receptor Agonists

ABSTRACT Toidentify new leads for the treatment of Plasmodium falciparum malaria, we screened a panel of serotonin (5-hydroxytryptamine [5HT]) receptor agonists and antagonists and determined their effects on parasite growth. The 5HT1A receptor agonists 8-hydroxy-N-(di-n-propyl)-aminotetralin (8-OH-DPAT), 2,5-dimethoxy-4-iodoamphetamine, and 2,5-dimethoxy-4-bromophenylethylamine inhibited the growth of P. falciparum in vitro (50% inhibitory concentrations, 0.4, 0.7, and 1.5 μM, respectively). In further characterizing the antiparasitic effects of 8-OH-DPAT, we found that this serotonin receptor agonist did not affect the growth of Leishmania infantum, Trypanosoma cruzi, Trypanosoma brucei brucei, or Trichostrongylus colubriformis in vitro and did not demonstrate cytotoxicity against the human lung fibroblast cell line MRC-5. 8-OH-DPAT had similar levels of growth inhibition against several different P. falciparum isolates having distinct chemotherapeutic resistance phenotypes, and its antimalarial effect was additive when it was used in combination with chloroquine against a chloroquine-resistant isolate. In a patch clamp assay, 8-OH-DPAT blocked a P. falciparum surface membrane channel, suggesting that serotonin receptor agonists are a novel class of antimalarials that target a nutrient transport pathway. Since there may be neurological involvement with the use of 8-OH-DPAT and other serotonin receptor agonists in the treatment of falciparum malaria, new lead compounds derived from 8-OH-DPAT will need to be modified to prevent potential neurological side effects. Nevertheless, these results suggest that 8-OH-DPAT is a new lead compound with which to derive novel antimalarial agents and is a useful tool with which to characterize P. falciparum membrane channels.

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