RESUMO
SignificanceMethanobactins (Mbns), copper-binding peptidic compounds produced by some bacteria, are candidate therapeutics for human diseases of copper overload. The paired oxazolone-thioamide bidentate ligands of methanobactins are generated from cysteine residues in a precursor peptide, MbnA, by the MbnBC enzyme complex. MbnBC activity depends on the presence of iron and oxygen, but the catalytically active form has not been identified. Here, we provide evidence that a dinuclear Fe(II)Fe(III) center in MbnB, which is the only representative of a >13,000-member protein family to be characterized, is responsible for this reaction. These findings expand the known roles of diiron enzymes in biology and set the stage for mechanistic understanding, and ultimately engineering, of the MbnBC biosynthetic complex.
Assuntos
Cisteína , Oxazolona , Cobre/metabolismo , Compostos Férricos/química , Humanos , Imidazóis , Oligopeptídeos , Oxigênio/metabolismo , TioamidasRESUMO
Hyperactivation of Ras-ERK1/2 signaling is critical to the development of many human malignancies, but little is known regarding the specific contribution of ERK1 or ERK2 to oncogenic processes. We demonstrate that ERK2 but not ERK1 signaling is necessary for Ras-induced epithelial-to-mesenchymal transformation (EMT). Further, ERK2 but not ERK1 overexpression is sufficient to induce EMT. Many ERK1/2-interacting proteins contain amino acid motifs, e.g., DEF or D-motifs, which regulate docking with ERK1/2. Remarkably, ERK2 signaling to DEF motif-containing targets is required to induce EMT and correlates with increased migration, invasion, and survival. Importantly, the late-response gene product Fra1 is necessary for Ras- and ERK2-induced EMT through upregulation of ZEB1/2 proteins. Thus, an apparent critical role for ERK2 DEF motif signaling during tumorigenesis is the regulation of Fra1 and the subsequent induction of ZEB1/2, suggesting a potential therapeutic target for Ras-regulated tumorigenesis.
Assuntos
Motivos de Aminoácidos , Diferenciação Celular/fisiologia , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Transdução de Sinais/fisiologia , Biomarcadores/metabolismo , Linhagem Celular Tumoral , Movimento Celular/fisiologia , Células Epiteliais/citologia , Células Epiteliais/fisiologia , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Humanos , Proteína Quinase 1 Ativada por Mitógeno/genética , Proteína Quinase 3 Ativada por Mitógeno/genética , Mutação , Proteínas Proto-Oncogênicas c-fos/genética , Proteínas Proto-Oncogênicas c-fos/metabolismo , Interferência de RNA , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Homeobox 2 de Ligação a E-box com Dedos de Zinco , Homeobox 1 de Ligação a E-box em Dedo de Zinco , Proteínas ras/genética , Proteínas ras/metabolismoRESUMO
Nearly every ciliated organism possesses three B9 domain-containing proteins: MKS1, B9D1, and B9D2. Mutations in human MKS1 cause Meckel syndrome (MKS), a severe ciliopathy characterized by occipital encephalocele, liver ductal plate malformations, polydactyly, and kidney cysts. Mouse mutations in either Mks1 or B9d2 compromise ciliogenesis and result in phenotypes similar to those of MKS. Given the importance of these two B9 proteins to ciliogenesis, we examined the role of the third B9 protein, B9d1. Mice lacking B9d1 displayed polydactyly, kidney cysts, ductal plate malformations, and abnormal patterning of the neural tube, concomitant with compromised ciliogenesis, ciliary protein localization, and Hedgehog (Hh) signal transduction. These data prompted us to screen MKS patients for mutations in B9D1 and B9D2. We identified a homozygous c.301A>C (p.Ser101Arg) B9D2 mutation that segregates with MKS, affects an evolutionarily conserved residue, and is absent from controls. Unlike wild-type B9D2 mRNA, the p.Ser101Arg mutation failed to rescue zebrafish phenotypes induced by the suppression of b9d2. With coimmunoprecipitation and mass spectrometric analyses, we found that Mks1, B9d1, and B9d2 interact physically, but that the p.Ser101Arg mutation abrogates the ability of B9d2 to interact with Mks1, further suggesting that the mutation compromises B9d2 function. Our data indicate that B9d1 is required for normal Hh signaling, ciliogenesis, and ciliary protein localization and that B9d1 and B9d2 are essential components of a B9 protein complex, disruption of which causes MKS.
Assuntos
Transtornos da Motilidade Ciliar/genética , Encefalocele/genética , Doenças Renais Policísticas/genética , Proteínas/genética , Sequência de Aminoácidos , Animais , Análise Mutacional de DNA , Ligação Genética , Homozigoto , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Dados de Sequência Molecular , Mutação , Células NIH 3T3 , Tubo Neural/anormalidades , Fenótipo , Polidactilia/genética , Transporte Proteico/genética , Proteínas/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Retinose Pigmentar , Transdução de Sinais , Peixe-Zebra/genéticaRESUMO
Skin and hair follicle morphogenesis and homeostasis require the integration of multiple signaling pathways, including Hedgehog (Hh) and Wingless (Wnt), and oriented cell divisions, all of which have been associated with primary cilia. Although studies have shown that disrupting dermal cilia causes follicular arrest and attenuated Hh signaling, little is known about the role of epidermal cilia. Here, epidermal cilia function was analyzed using conditional alleles of the ciliogenic genes Ift88 and Kif3a. At birth, epidermal cilia mutants appeared normal, but developed basaloid hyperplasia and ingrowths into the dermis of the ventrum with age. In addition, follicles in the tail were disorganized and had excess sebaceous gland lobules. Epidermal cilia mutants displayed fewer long-term label-retaining cells, suggesting altered stem cell homeostasis. Abnormal proliferation and differentiation were evident from lineage-tracing studies and showed an expansion of follicular cells into the interfollicular epidermis, as is seen during wound repair. These phenotypes were not associated with changes in canonical Wnt activity or oriented cell division. However, nuclear accumulation of the ΔNp63 transcription factor, which is involved in stratification, keratinocyte differentiation and wound repair, was increased, whereas the Hh pathway was repressed. Intriguingly, the phenotypes were not typical of those associated with loss of Hh signaling but exhibited similarities with those of mice in which ΔNp63 is overexpressed in the epidermis. Collectively, these data indicate that epidermal primary cilia may function in stress responses and epidermal homeostasis involving pathways other than those typically associated with primary cilia.
Assuntos
Cílios/fisiologia , Células Epidérmicas , Folículo Piloso/fisiologia , Homeostase/fisiologia , Fenômenos Fisiológicos da Pele , Animais , Animais Recém-Nascidos , Cílios/genética , Cílios/metabolismo , Epiderme/metabolismo , Epiderme/fisiologia , Regulação da Expressão Gênica no Desenvolvimento , Folículo Piloso/citologia , Folículo Piloso/metabolismo , Homeostase/genética , Integrases/genética , Integrases/metabolismo , Cinesinas/genética , Cinesinas/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Fenótipo , Fenômenos Fisiológicos da Pele/genética , Transgenes/genética , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismoRESUMO
Genetic engineering of allogeneic cell therapeutics that fully prevents rejection by a recipient's immune system would abolish the requirement for immunosuppressive drugs or encapsulation and support large-scale manufacturing of off-the-shelf cell products. Previously, we generated mouse and human hypoimmune pluripotent (HIP) stem cells by depleting HLA class I and II molecules and overexpressing CD47 (B2M-/-CIITA-/-CD47+). To determine whether this strategy is successful in non-human primates, we engineered rhesus macaque HIP cells and transplanted them intramuscularly into four allogeneic rhesus macaques. The HIP cells survived unrestricted for 16 weeks in fully immunocompetent allogeneic recipients and differentiated into several lineages, whereas allogeneic wild-type cells were vigorously rejected. We also differentiated human HIP cells into endocrinologically active pancreatic islet cells and showed that they survived in immunocompetent, allogeneic diabetic humanized mice for 4 weeks and ameliorated diabetes. HIP-edited primary rhesus macaque islets survived for 40 weeks in an allogeneic rhesus macaque recipient without immunosuppression, whereas unedited islets were quickly rejected.
Assuntos
Transplante de Células-Tronco Hematopoéticas , Células-Tronco Pluripotentes Induzidas , Transplante das Ilhotas Pancreáticas , Camundongos , Animais , Macaca mulatta , Antígeno CD47 , Rejeição de EnxertoRESUMO
Eukaryotic translation initiation factor 2B (eIF2B) is a key component of the integrated stress response (ISR), which regulates protein synthesis and stress granule formation in response to cellular insult. Modulation of the ISR has been proposed as a therapeutic strategy for treatment of neurodegenerative diseases such as vanishing white matter (VWM) disease and amyotrophic lateral sclerosis (ALS) based on its ability to improve cellular homeostasis and prevent neuronal degeneration. Herein, we report the small-molecule discovery campaign that identified potent, selective, and CNS-penetrant eIF2B activators using both structure- and ligand-based drug design. These discovery efforts culminated in the identification of DNL343, which demonstrated a desirable preclinical drug profile, including a long half-life and high oral bioavailability across preclinical species. DNL343 was progressed into clinical studies and is currently undergoing evaluation in late-stage clinical trials for ALS.
Assuntos
Esclerose Lateral Amiotrófica , Leucoencefalopatias , Doenças Neurodegenerativas , Humanos , Doenças Neurodegenerativas/tratamento farmacológico , Doenças Neurodegenerativas/metabolismo , Esclerose Lateral Amiotrófica/tratamento farmacológico , Esclerose Lateral Amiotrófica/metabolismo , Mutação , Fator de Iniciação 2B em Eucariotos/genética , Fator de Iniciação 2B em Eucariotos/metabolismo , Encéfalo/metabolismo , Leucoencefalopatias/metabolismoRESUMO
The role of primary cilia in the gastrointestinal tract has not been examined. Here we report the presence of primary cilia on gastric endocrine cells producing gastrin, ghrelin, and somatostatin (Sst), hormones regulated by food intake. During eating, cilia in the gastric antrum decreased, whereas gastric acid and circulating gastrin increased. Mice fed high-fat chow showed a delayed decrease in antral cilia, increased plasma gastrin, and gastric acidity. Mice fed high-fat chow for 3 wk showed lower cilia numbers and acid but higher gastrin levels than mice fed a standard diet, suggesting that fat affects gastric physiology. Ex vivo experiments showed that cilia in the corpus responded to acid and distension, whereas cilia in the antrum responded to food. To analyze the role of gastric cilia, we conditionally deleted the intraflagellar transport protein Ift88 (Ift88(-/fl)). In fed Ift88(-/fl) mice, gastrin levels were higher, and gastric acidity was lower. Moreover, gastrin and Sst gene expression did not change in response to food as in controls. At 8 mo, Ift88(-/fl) mice developed foveolar hyperplasia, hypergastrinemia, and hypochlorhydria associated with endocrine dysfunction. Our results show that components of food (fat) are sensed by antral cilia on endocrine cells, which modulates gastrin secretion and gastric acidity.
Assuntos
Cílios/fisiologia , Ácido Gástrico/metabolismo , Mucosa Gástrica/metabolismo , Gastrinas/fisiologia , Animais , Dieta Hiperlipídica , Feminino , Alimentos , Grelina/biossíntese , Hiperplasia/genética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Antro Pilórico , Estômago/patologia , Estômago/ultraestrutura , Proteínas Supressoras de Tumor/deficiênciaRESUMO
Manufacturing autologous chimeric antigen receptor (CAR) T cell therapeutics is complex, and many patients experience treatment delays or cannot be treated at all. Although current allogeneic CAR products have the potential to overcome manufacturing bottlenecks, they are subject to immune rejection and failure to persist in the host, and thus do not provide the same level of efficacy as their autologous counterparts. Here, we aimed to develop universal allogeneic CAR T cells that evade the immune system and produce a durable response. We generated human hypoimmune (HIP) T cells with disrupted B2M, CIITA, and TRAC genes using CRISPR-Cas9 editing. In addition, CD47 and anti-CD19 CAR were expressed using lentiviral transduction. These allogeneic HIP CD19 CAR T cells were compared to allogeneic CD19 CAR T cells that only expressed the anti-CD19 CAR (allo CAR T). In vitro assays for cancer killing and exhaustion revealed no differences between allo CAR T and HIP CAR T cells, confirming that the HIP edits did not negatively affect T cell performance. Clearance of CD19+ tumors by HIP CAR T cells in immunodeficient NSG mice was comparable to that of allo CAR T cells. In fully immunocompetent humanized mice, HIP CAR T cells significantly outperformed allo CAR T cells, showed improved persistence and expansion, and provided lasting cancer clearance. Furthermore, CD47-targeting safety strategies reliably and specifically eliminated HIP CAR T cells. These findings suggest that universal allogeneic HIP CAR T cell-based therapeutics might overcome the limitations associated with poor persistence of allogeneic CAR T cells and exert durable anti-tumor responses.
Assuntos
Transplante de Células-Tronco Hematopoéticas , Neoplasias , Receptores de Antígenos Quiméricos , Humanos , Camundongos , Animais , Receptores de Antígenos Quiméricos/genética , Antígeno CD47 , Linfócitos T , Receptores de Antígenos de Linfócitos T/genéticaRESUMO
Transplantation of allogeneic pancreatic donor islets has successfully been performed in selected patients with difficult-to-control insulin-dependent diabetes and impaired awareness of hypoglycemia (IAH). However, the required systemic immunosuppression associated with this procedure prevents this cell replacement therapy from more widespread adoption in larger patient populations. We report the editing of primary human islet cells to the hypoimmune HLA class I- and class II-negative and CD47-overexpressing phenotype and their reaggregation into human HIP pseudoislets (p-islets). Human HIP p-islets were shown to survive, engraft, and ameliorate diabetes in immunocompetent, allogeneic, diabetic humanized mice. HIP p-islet cells were further shown to avoid autoimmune killing in autologous, diabetic humanized autoimmune mice. The survival and endocrine function of HIP p-islet cells were not impaired by contamination of unedited or partially edited cells within the p-islets. HIP p-islet cells were eliminated quickly and reliably in this model using a CD47-targeting antibody, thus providing a safety strategy in case HIP cells exert toxicity in a future clinical setting. Transplantation of human HIP p-islets for which no immunosuppression is required has the potential to lead to wider adoption of this therapy and help more diabetes patients with IAH and history of severe hypoglycemic events to achieve insulin independence.
Assuntos
Diabetes Mellitus Tipo 1 , Transplante de Células-Tronco Hematopoéticas , Transplante das Ilhotas Pancreáticas , Ilhotas Pancreáticas , Humanos , Animais , Camundongos , Antígeno CD47 , Transplante das Ilhotas Pancreáticas/métodos , Autoimunidade , Diabetes Mellitus Tipo 1/terapia , InsulinaRESUMO
SUPT4H1 is a transcription elongation factor that makes up part of the RNA polymerase II complex. Recent studies propose a selective role for SUPT4H1 in the transcription of repeat-containing DNA, the translated products of which contribute to neurodegenerative disorders such as C9orf72-amyotrophic lateral sclerosis. To investigate the potential of SUPT4H1 as a therapeutic target in repeat-associated neurodegeneration, we depleted SUPT4H1 by RNA interference to inhibit the function of the SUPT4H1/SUPT5H transcription elongation complex. Depletion of SUPT4H1 leads to a global reduction in all cellular RNA, highlighting the significant challenges that are associated with targeting this molecule for the treatment of human disease. Any requirement of SUPT4H1 for transcription of specific transcripts should be interpreted in the context of global modulatory effects on the transcriptome.
Assuntos
RNA/metabolismo , Proteínas Repressoras/deficiência , Células A549 , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/metabolismo , Técnicas de Silenciamento de Genes , Células HEK293 , Células HeLa , Humanos , RNA/biossíntese , RNA/genética , Interferência de RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Ribossomos/genética , Ribossomos/metabolismo , Fatores de Elongação da Transcrição/genética , Fatores de Elongação da Transcrição/metabolismoRESUMO
Stress granules (SGs) form during cellular stress and are implicated in neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). To yield insights into the role of SGs in pathophysiology, we performed a high-content screen to identify small molecules that alter SG properties in proliferative cells and human iPSC-derived motor neurons (iPS-MNs). One major class of active molecules contained extended planar aromatic moieties, suggesting a potential to intercalate in nucleic acids. Accordingly, we show that several hit compounds can prevent the RNA-dependent recruitment of the ALS-associated RNA-binding proteins (RBPs) TDP-43, FUS, and HNRNPA2B1 into SGs. We further demonstrate that transient SG formation contributes to persistent accumulation of TDP-43 into cytoplasmic puncta and that our hit compounds can reduce this accumulation in iPS-MNs from ALS patients. We propose that compounds with planar moieties represent a promising starting point to develop small-molecule therapeutics for treating ALS/FTD.
Assuntos
Esclerose Lateral Amiotrófica/metabolismo , Grânulos Citoplasmáticos/efeitos dos fármacos , Proteínas de Ligação a DNA/efeitos dos fármacos , Demência Frontotemporal/metabolismo , Neurônios Motores/efeitos dos fármacos , Agregação Patológica de Proteínas/metabolismo , Bibliotecas de Moléculas Pequenas/farmacologia , Estresse Fisiológico/efeitos dos fármacos , Linhagem Celular , Grânulos Citoplasmáticos/metabolismo , DNA Helicases/genética , Proteínas de Ligação a DNA/metabolismo , Células HEK293 , Ribonucleoproteínas Nucleares Heterogêneas Grupo A-B/metabolismo , Ensaios de Triagem em Larga Escala , Humanos , Células-Tronco Pluripotentes Induzidas , Proteínas Intrinsicamente Desordenadas , Neurônios Motores/metabolismo , Células-Tronco Neurais/efeitos dos fármacos , Células-Tronco Neurais/metabolismo , Proteínas de Ligação a Poli-ADP-Ribose/genética , RNA Helicases/genética , Proteínas com Motivo de Reconhecimento de RNA/genética , Proteína FUS de Ligação a RNA/metabolismoRESUMO
Inhibitors of the oncogenic Ras-MAPK pathway have been intensely pursued as therapeutics. Targeting this pathway, however, presents challenges due to the essential role of MAPK in homeostatic functions. The phosphorylation and activation of MAPK substrates is regulated by protein-protein interactions with MAPK docking sites. Active ERK1/2 (extracellular signal-regulated kinase 1/2)-MAPKs localize to effectors containing DEF (docking site for ERK, (F)/(Y) -X-(F)/(Y) -P)- or D-domain (docking domain) motifs. We have examined the in vivo activity of ERK2 mutants with impaired ability to signal via either docking site. Mutations in the DEF-domain binding pocket prevent activation of DEF-domain-containing effectors but not RSK (90 kDa ribosomal S6 kinase), which contains a D domain. Conversely, mutation of the ERK2 CD domain, which interacts with D domains, prevents RSK activation but not DEF-domain signaling. Uncoupling docking interactions does not compromise ERK2 phosphotransferase activity. ERK2 DEF mutants undergo regulated nuclear translocation but are defective for Elk-1/TCF transactivation and target gene induction. Thus, downstream branches of ERK2 signaling can be selectively inhibited without blocking total pathway activity. Significantly, several protooncogenes contain DEF domains and are regulated by ERK1/2. Therefore, disrupting ERK-DEF domain interactions could be an alternative to inhibiting oncogenic Ras-MAPK signaling.
Assuntos
Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Modelos Moleculares , Transdução de Sinais/fisiologia , Animais , Sequência de Bases , Western Blotting , Imunofluorescência , Células HeLa , Humanos , Camundongos , Proteína Quinase 1 Ativada por Mitógeno/genética , Mutagênese Sítio-Dirigida , Mutação/genética , Células NIH 3T3 , Ligação Proteica , Proteínas Quinases/metabolismo , Estrutura Terciária de Proteína , RNA Interferente Pequeno/genética , Proteínas Quinases S6 RibossômicasRESUMO
Iron is vital for many homeostatic processes, and its liberation from ferritin nanocages occurs in the lysosome. Studies indicate that ferritin and its binding partner nuclear receptor coactivator-4 (NCOA4) are targeted to lysosomes by a form of selective autophagy. By using genome-scale functional screening, we identify an alternative lysosomal transport pathway for ferritin that requires FIP200, ATG9A, VPS34, and TAX1BP1 but lacks involvement of the ATG8 lipidation machinery that constitutes classical macroautophagy. TAX1BP1 binds directly to NCOA4 and is required for lysosomal trafficking of ferritin under basal and iron-depleted conditions. Under basal conditions ULK1/2-FIP200 controls ferritin turnover, but its deletion leads to TAX1BP1-dependent activation of TBK1 that regulates redistribution of ATG9A to the Golgi enabling continued trafficking of ferritin. Cells expressing an amyotrophic lateral sclerosis (ALS)-associated TBK1 allele are incapable of degrading ferritin suggesting a molecular mechanism that explains the presence of iron deposits in patient brain biopsies.
Assuntos
Proteína Homóloga à Proteína-1 Relacionada à Autofagia/metabolismo , Proteínas Relacionadas à Autofagia/metabolismo , Autofagia/fisiologia , DNA Complementar/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Lisossomos/metabolismo , Proteínas de Membrana/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Tirosina Quinases/metabolismo , Proteínas de Transporte Vesicular/metabolismo , Autofagia/genética , Proteína Homóloga à Proteína-1 Relacionada à Autofagia/genética , Proteínas Relacionadas à Autofagia/genética , Linhagem Celular , Linhagem Celular Tumoral , Ferritinas/genética , Ferritinas/metabolismo , Células HEK293 , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/genética , Proteínas de Membrana/genética , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Proteínas Serina-Treonina Quinases/genética , Proteínas Tirosina Quinases/genética , Proteínas de Transporte Vesicular/genéticaRESUMO
Autophagy is a dynamic process that regulates lysosomal-dependent degradation of cellular components. Until recently the study of autophagy has been hampered by the lack of reliable pharmacological tools, but selective inhibitors are now available to modulate the PI 3-kinase VPS34, which is required for autophagy. Here we describe the discovery of potent and selective VPS34 inhibitors, their pharmacokinetic (PK) properties, and ability to inhibit autophagy in cellular and mouse models.
RESUMO
The Meckel syndrome (MKS) complex functions at the transition zone, located between the basal body and axoneme, to regulate the localization of ciliary membrane proteins. We investigated the role of Tmem231, a two-pass transmembrane protein, in MKS complex formation and function. Consistent with a role in transition zone function, mutation of mouse Tmem231 disrupts the localization of proteins including Arl13b and Inpp5e to cilia, resulting in phenotypes characteristic of MKS such as polydactyly and kidney cysts. Tmem231 and B9d1 are essential for each other and other complex components such as Mks1 to localize to the transition zone. As in mouse, the Caenorhabditis elegans orthologue of Tmem231 localizes to and controls transition zone formation and function, suggesting an evolutionarily conserved role for Tmem231. We identified TMEM231 mutations in orofaciodigital syndrome type 3 (OFD3) and MKS patients that compromise transition zone function. Thus, Tmem231 is critical for organizing the MKS complex and controlling ciliary composition, defects in which cause OFD3 and MKS.
Assuntos
Cílios/metabolismo , Transtornos da Motilidade Ciliar/genética , Encefalocele/genética , Proteínas de Membrana/genética , Síndromes Orofaciodigitais/genética , Doenças Renais Policísticas/genética , Animais , Células COS , Caenorhabditis elegans , Chlorocebus aethiops , Cílios/patologia , Proteínas do Citoesqueleto , Células HEK293 , Humanos , Proteínas de Membrana/fisiologia , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Mutação de Sentido Incorreto , Proteínas/metabolismo , Retinose PigmentarRESUMO
Cells rely on autophagy to clear misfolded proteins and damaged organelles to maintain cellular homeostasis. In this study we use the new autophagy inhibitor PIK-III to screen for autophagy substrates. PIK-III is a selective inhibitor of VPS34 that binds a unique hydrophobic pocket not present in related kinases such as PI(3)Kα. PIK-III acutely inhibits autophagy and de novo lipidation of LC3, and leads to the stabilization of autophagy substrates. By performing ubiquitin-affinity proteomics on PIK-III-treated cells we identified substrates including NCOA4, which accumulates in ATG7-deficient cells and co-localizes with autolysosomes. NCOA4 directly binds ferritin heavy chain-1 (FTH1) to target the iron-binding ferritin complex with a relative molecular mass of 450,000 to autolysosomes following starvation or iron depletion. Interestingly, Ncoa4(-/-) mice exhibit a profound accumulation of iron in splenic macrophages, which are critical for the reutilization of iron from engulfed red blood cells. Taken together, the results of this study provide a new mechanism for selective autophagy of ferritin and reveal a previously unappreciated role for autophagy and NCOA4 in the control of iron homeostasis in vivo.
Assuntos
Autofagia/fisiologia , Classe III de Fosfatidilinositol 3-Quinases/antagonistas & inibidores , Ferritinas/metabolismo , Homeostase/fisiologia , Ferro/metabolismo , Coativadores de Receptor Nuclear/metabolismo , Animais , Autofagia/efeitos dos fármacos , Células Cultivadas , Humanos , Lisossomos/metabolismo , Camundongos , Fagossomos/metabolismo , Ligação ProteicaRESUMO
Primary cilia are microtubule-based organelles involved in signal transduction and project from the surface of most vertebrate cells. Proteins that can localize to the cilium, for example, Inversin and Bardet-Biedl syndrome (BBS) proteins, are implicated in both beta-catenin-dependent and -independent Wnt signalling. Given that Inversin and BBS proteins are found both at the cilium and elsewhere in the cell, the role of the cilium itself in Wnt signalling is not clear. Using three separate mutations that disrupt ciliogenesis (affecting Kif3a, Ift88 and Ofd1), we show in this study that the primary cilium restricts the activity of the canonical Wnt pathway in mouse embryos, primary fibroblasts, and embryonic stem cells. Interestingly, unciliated cells activate transcription only in response to Wnt stimulation, but do so much more robustly than ciliated cells. Loss of Kif3a, but not other ciliogenic genes, causes constitutive phosphorylation of Dishevelled (Dvl). Blocking the activity of casein kinase I (CKI) reverses this constitutive Dvl phosphorylation and abrogates pathway hyper-responsiveness. These results suggest that Kif3a restrains canonical Wnt signalling both by restricting the CKI-dependent phosphorylation of Dvl and through a separate ciliary mechanism. More generally, these findings reveal that, in contrast to its role in promoting Hedgehog (Hh) signalling, the cilium restrains canonical Wnt signalling.