RESUMO
Aspergillus fumigatus is the predominant mould pathogen for humans. Adaption to host-imposed iron limitation has previously been demonstrated to be essential for its virulence. [2Fe-2S] clusters are crucial as cofactors of several metabolic pathways and mediate cytosolic/nuclear iron sensing in fungi including A. fumigatus. [2Fe-2S] cluster trafficking has been shown to involve BolA family proteins in both mitochondria and the cytosol/nucleus. Interestingly, both A. fumigatus homologues, termed Bol1 and Bol3, possess mitochondrial targeting sequences, suggesting the lack of cytosolic/nuclear versions. Here, we show by the combination of mutational, proteomic and fluorescence microscopic analyses that expression of the Bol3 encoding gene leads to dual localization of gene products to mitochondria and the cytosol/nucleus via alternative translation initiation downstream of the mitochondrial targeting sequence, which appears to be highly conserved in various Aspergillus species. Lack of either mitochondrial Bol1 or Bol3 was phenotypically inconspicuous while lack of cytosolic/nuclear Bol3 impaired growth during iron limitation but not iron sensing which indicates a particular importance of [2Fe-2S] cluster trafficking during iron limitation. Remarkably, cytosolic/nuclear Bol3 differs from the mitochondrial version only by N-terminal acetylation, a finding that was only possible by mutational hypothesis testing.
Assuntos
Aspergillus fumigatus , Citosol , Proteínas Fúngicas , Ferro , Mitocôndrias , Aspergillus fumigatus/metabolismo , Aspergillus fumigatus/genética , Proteínas Fúngicas/metabolismo , Proteínas Fúngicas/genética , Citosol/metabolismo , Mitocôndrias/metabolismo , Ferro/metabolismo , Adaptação Fisiológica , Núcleo Celular/metabolismo , Transporte Proteico , Proteômica/métodos , Proteínas Ferro-Enxofre/metabolismo , Proteínas Ferro-Enxofre/genética , Regulação Fúngica da Expressão Gênica , AcetilaçãoRESUMO
The neurodevelopmental disorders Prader-Willi syndrome (PWS) and Schaaf-Yang syndrome (SYS) both arise from genomic alterations within human chromosome 15q11-q13. A deletion of the SNORD116 cluster, encoding small nucleolar RNAs, or frameshift mutations within MAGEL2 result in closely related phenotypes in individuals with PWS or SYS, respectively. By investigation of their subcellular localization, we observed that in contrast to a predominant cytoplasmic localization of wild-type (WT) MAGEL2, a truncated MAGEL2 mutant was evenly distributed between the cytoplasm and the nucleus. To elucidate regulatory pathways that may underlie both diseases, we identified protein interaction partners for WT or mutant MAGEL2, in particular the survival motor neuron protein (SMN), involved in spinal muscular atrophy, and the fragile-X-messenger ribonucleoprotein (FMRP), involved in autism spectrum disorders. The interactome of the non-coding RNA SNORD116 was also investigated by RNA-CoIP. We show that WT and truncated MAGEL2 were both involved in RNA metabolism, while regulation of transcription was mainly observed for WT MAGEL2. Hence, we investigated the influence of MAGEL2 mutations on the expression of genes from the PWS locus, including the SNORD116 cluster. Thereby, we provide evidence for MAGEL2 mutants decreasing the expression of SNORD116, SNORD115, and SNORD109A, as well as protein-coding genes MKRN3 and SNRPN, thus bridging the gap between PWS and SYS.
Assuntos
Peptídeos e Proteínas de Sinalização Intracelular , Proteínas Intrinsicamente Desordenadas , Síndrome de Prader-Willi , Humanos , Cromossomos Humanos Par 15/genética , Citoplasma/metabolismo , Células HEK293 , Mutação , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Síndrome de Prader-Willi/genética , Proteínas/genética , Proteínas/metabolismo , RNA Nucleolar Pequeno/genéticaRESUMO
Alzheimer's disease (AD) pathology is characterized by amyloid beta (Aß) plaques and dysfunctional autophagy. Aß is generated by sequential proteolytic cleavage of amyloid precursor protein (APP), and the site of intracellular APP processing is highly debated, which may include autophagosomes. Here, we investigated the involvement of autophagy, including the role of ATG9 in APP intracellular trafficking and processing by applying the RUSH system, which allows studying the transport of fluorescently labeled mCherry-APP-EGFP in a systematic way, starting from the endoplasmic reticulum. HeLa cells, expressing the RUSH mCherry-APP-EGFP system, were investigated by live cell imaging, immunofluorescence, and Western blot. We found that mCherry-APP-EGFP passed through the Golgi faster in ATG9 knockout cells. Furthermore, ATG9 deletion shifted mCherry-APP-EGFP from early endosomes and lysosomes toward the plasma membrane concomitant with reduced endocytosis. Importantly, this alteration in mCherry-APP-EGFP transport resulted in increased secreted mCherry-soluble APP and C-terminal fragment-EGFP. These effects were also phenocopied by pharmacological inhibition of ULK1, indicating that autophagy is regulating the intracellular trafficking and processing of APP. These findings contribute to the understanding of the role of autophagy in APP metabolism and could potentially have implications for new therapeutic approaches for AD.
Assuntos
Doença de Alzheimer , Precursor de Proteína beta-Amiloide , Humanos , Peptídeos beta-Amiloides , Células HeLa , Transporte Biológico , AutofagiaRESUMO
TransitID is a new methodology based on proximity labeling allowing for the study of protein trafficking a the proteome scale.
Assuntos
Proteoma , Proteômica , Proteoma/metabolismo , Proteômica/métodos , Transporte ProteicoRESUMO
Mechanobiology studies the mechanisms by which cells sense and respond to physical forces, and the role of these forces in shaping cells and tissues themselves. Mechanosensing can occur at the plasma membrane, which is directly exposed to external forces, but also in the cell's interior, for example, through deformation of the nucleus. Less is known on how the function and morphology of organelles are influenced by alterations in their own mechanical properties, or by external forces. Here, we discuss recent advances on the mechanosensing and mechanotransduction of organelles, including the endoplasmic reticulum (ER), the Golgi apparatus, the endo-lysosmal system, and the mitochondria. We highlight open questions that need to be addressed to gain a broader understanding of the role of organelle mechanobiology.
Assuntos
Mecanotransdução Celular , Organelas , Humanos , Organelas/metabolismo , Complexo de Golgi/metabolismo , Retículo Endoplasmático/metabolismo , Mitocôndrias/metabolismo , Membrana Celular/metabolismoRESUMO
Our understanding of how speed and persistence of cell migration affects the growth rate and size of tumors remains incomplete. To address this, we developed a mathematical model wherein cells migrate in two-dimensional space, divide, die or intravasate into the vasculature. Exploring a wide range of speed and persistence combinations, we find that tumor growth positively correlates with increasing speed and higher persistence. As a biologically relevant example, we focused on Golgi fragmentation, a phenomenon often linked to alterations of cell migration. Golgi fragmentation was induced by depletion of Giantin, a Golgi matrix protein, the downregulation of which correlates with poor patient survival. Applying the experimentally obtained migration and invasion traits of Giantin depleted breast cancer cells to our mathematical model, we predict that loss of Giantin increases the number of intravasating cells. This prediction was validated, by showing that circulating tumor cells express significantly less Giantin than primary tumor cells. Altogether, our computational model identifies cell migration traits that regulate tumor progression and uncovers a role of Giantin in breast cancer progression.
Assuntos
Neoplasias da Mama , Proteínas de Membrana , Humanos , Feminino , Proteínas de Membrana/metabolismo , Proteínas da Matriz do Complexo de Golgi/metabolismo , Neoplasias da Mama/metabolismo , Complexo de Golgi/metabolismo , Complexo de Golgi/patologiaRESUMO
Osteogenesis imperfecta (OI) is a genetically and clinically heterogeneous disorder characterized by bone fragility and reduced bone mass generally caused by defects in type I collagen structure or defects in proteins interacting with collagen processing. We identified a homozygous missense mutation in SEC16B in a child with vertebral fractures, leg bowing, short stature, muscular hypotonia, and bone densitometric and histomorphometric features in keeping with OI with distinct ultrastructural features. In line with the putative function of SEC16B as a regulator of trafficking between the ER and the Golgi complex, we showed that patient fibroblasts accumulated type I procollagen in the ER and exhibited a general trafficking defect at the level of the ER. Consequently, patient fibroblasts exhibited ER stress, enhanced autophagosome formation, and higher levels of apoptosis. Transfection of wild-type SEC16B into patient cells rescued the collagen trafficking. Mechanistically, we show that the defect is a consequence of reduced SEC16B expression, rather than due to alterations in protein function. These data suggest SEC16B as a recessive candidate gene for OI.
Assuntos
Colágeno Tipo I , Osteogênese Imperfeita , Criança , Humanos , Colágeno/genética , Colágeno Tipo I/genética , Colágeno Tipo I/química , Colágeno Tipo I/metabolismo , Mutação , Osteogênese Imperfeita/genética , Osteogênese Imperfeita/metabolismo , Estresse do Retículo EndoplasmáticoRESUMO
Cells are constantly exposed to various chemical and physical stimuli. While much has been learned about the biochemical factors that regulate secretory trafficking from the endoplasmic reticulum (ER), much less is known about whether and how this trafficking is subject to regulation by mechanical signals. Here, we show that subjecting cells to mechanical strain both induces the formation of ER exit sites (ERES) and accelerates ER-to-Golgi trafficking. We found that cells with impaired ERES function were less capable of expanding their surface area when placed under mechanical stress and were more prone to develop plasma membrane defects when subjected to stretching. Thus, coupling of ERES function to mechanotransduction appears to confer resistance of cells to mechanical stress. Furthermore, we show that the coupling of mechanotransduction to ERES formation was mediated via a previously unappreciated ER-localized pool of the small GTPase Rac1. Mechanistically, we show that Rac1 interacts with the small GTPase Sar1 to drive budding of COPII carriers and stimulates ER-to-Golgi transport. This interaction therefore represents an unprecedented link between mechanical strain and export from the ER.
Assuntos
Mecanotransdução Celular , Proteínas Monoméricas de Ligação ao GTP , Transporte Biológico , Vesículas Revestidas pelo Complexo de Proteína do Envoltório/metabolismo , Retículo Endoplasmático/metabolismo , Complexo de Golgi/metabolismo , Proteínas Monoméricas de Ligação ao GTP/metabolismo , Transporte Proteico/fisiologiaRESUMO
BACKGROUND AND AIMS: Netrin-1 displays protumoral properties, though the pathological contexts and processes involved in its induction remain understudied. The liver is a major model of inflammation-associated cancer development, leading to HCC. APPROACH AND RESULTS: A panel of cell biology and biochemistry approaches (reverse transcription quantitative polymerase chain reaction, reporter assays, run-on, polysome fractionation, cross linking immunoprecipitation, filter binding assay, subcellular fractionation, western blotting, immunoprecipitation, stable isotope labeling by amino acids in cell culture) on in vitro-grown primary hepatocytes, human liver cell lines, mouse samples and clinical samples was used. We identify netrin-1 as a hepatic inflammation-inducible factor and decipher its mode of activation through an exhaustive eliminative approach. We show that netrin-1 up-regulation relies on a hitherto unknown mode of induction, namely its exclusive translational activation. This process includes the transfer of NTN1 (netrin-1) mRNA to the endoplasmic reticulum and the direct interaction between the Staufen-1 protein and this transcript as well as netrin-1 mobilization from its cell-bound form. Finally, we explore the impact of a phase 2 clinical trial-tested humanized anti-netrin-1 antibody (NP137) in two distinct, toll-like receptor (TLR) 2/TLR3/TLR6-dependent, hepatic inflammatory mouse settings. We observe a clear anti-inflammatory activity indicating the proinflammatory impact of netrin-1 on several chemokines and Ly6C+ macrophages. CONCLUSIONS: These results identify netrin-1 as an inflammation-inducible factor in the liver through an atypical mechanism as well as its contribution to hepatic inflammation.
Assuntos
Carcinoma Hepatocelular , Neoplasias Hepáticas , Camundongos , Humanos , Animais , Receptor 2 Toll-Like , Fatores de Crescimento Neural/metabolismo , Receptor 3 Toll-Like , Receptor 6 Toll-Like , Proteínas Supressoras de Tumor/metabolismo , Inflamação/metabolismo , Anti-Inflamatórios , RNA Mensageiro , Aminoácidos , Receptores de NetrinaRESUMO
Despite the strong evidence linking the aggregation of the Huntingtin protein (Htt) to the pathogenesis of Huntington's disease (HD), the mechanisms underlying Htt aggregation and neurodegeneration remain poorly understood. Herein, we investigated the ultrastructural properties and protein composition of Htt cytoplasmic and nuclear inclusions in mammalian cells and primary neurons overexpressing mutant exon1 of the Htt protein. Our findings provide unique insight into the ultrastructural properties of cytoplasmic and nuclear Htt inclusions and their mechanisms of formation. We show that Htt inclusion formation and maturation are complex processes that, although initially driven by polyQ-dependent Htt aggregation, also involve the polyQ and PRD domain-dependent sequestration of lipids and cytoplasmic and cytoskeletal proteins related to HD dysregulated pathways; the recruitment and accumulation of remodeled or dysfunctional membranous organelles, and the impairment of the protein quality control and degradation machinery. We also show that nuclear and cytoplasmic Htt inclusions exhibit distinct biochemical compositions and ultrastructural properties, suggesting different mechanisms of aggregation and toxicity.
Assuntos
Núcleo Celular/metabolismo , Citoplasma/metabolismo , Proteína Huntingtina/química , Proteína Huntingtina/metabolismo , Neurônios/metabolismo , Animais , Células HEK293 , Humanos , Proteína Huntingtina/genética , Proteína Huntingtina/ultraestrutura , Doença de Huntington/metabolismo , Corpos de Inclusão Intranuclear/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Peptídeos/química , Agregação Patológica de Proteínas , ProteomaRESUMO
In this article we discuss implications of the recent discovery of glycoRNAs found to be present at the cell surface of mammalian cells which was reported by Flynn et al. Cell 2021.
Assuntos
Polissacarídeos , RNA , Animais , Membrana Celular/metabolismo , Mamíferos/metabolismo , Polissacarídeos/metabolismoRESUMO
The HIV-protease inhibitor nelfinavir has shown broad anticancer activity in various preclinical and clinical contexts. In patients with advanced, proteasome inhibitor (PI)-refractory multiple myeloma, nelfinavir-based therapy resulted in 65% partial response or better, suggesting that this may be a highly active chemotherapeutic option in this setting. The broad anticancer mechanism of action of nelfinavir implies that it interferes with fundamental aspects of cancer cell biology. We combined proteome-wide affinity-purification of nelfinavir-interacting proteins with genome-wide CRISPR/Cas9-based screening to identify protein partners that interact with nelfinavir in an activity-dependent manner alongside candidate genetic contributors affecting nelfinavir cytotoxicity. Nelfinavir had multiple activity-specific binding partners embedded in lipid bilayers of mitochondria and the endoplasmic reticulum. Nelfinavir affected the fluidity and composition of lipid-rich membranes, disrupted mitochondrial respiration, blocked vesicular transport, and affected the function of membrane-embedded drug efflux transporter ABCB1, triggering the integrated stress response. Sensitivity to nelfinavir was dependent on ADIPOR2, which maintains membrane fluidity by promoting fatty acid desaturation and incorporation into phospholipids. Supplementation with fatty acids prevented the nelfinavir-induced effect on mitochondrial metabolism, drug-efflux transporters, and stress-response activation. Conversely, depletion of fatty acids/cholesterol pools by the FDA-approved drug ezetimibe showed a synergistic anticancer activity with nelfinavir in vitro. These results identify the modification of lipid-rich membranes by nelfinavir as a novel mechanism of action to achieve broad anticancer activity, which may be suitable for the treatment of PI-refractory multiple myeloma. SIGNIFICANCE: Nelfinavir induces lipid bilayer stress in cellular organelles that disrupts mitochondrial respiration and transmembrane protein transport, resulting in broad anticancer activity via metabolic rewiring and activation of the unfolded protein response.
Assuntos
Inibidores da Protease de HIV/farmacologia , Lipídeos de Membrana , Mieloma Múltiplo/tratamento farmacológico , Mieloma Múltiplo/metabolismo , Nelfinavir/farmacologia , Subfamília B de Transportador de Cassetes de Ligação de ATP/metabolismo , Antineoplásicos/farmacologia , Sistemas CRISPR-Cas , Linhagem Celular Tumoral , Retículo Endoplasmático/metabolismo , Genoma , Glucose/metabolismo , Complexo de Golgi/metabolismo , Células HEK293 , Humanos , Lipidômica , Lipídeos/química , Fosfolipídeos/química , Fosforilação , Receptores de Adiponectina/metabolismo , Transdução de SinaisRESUMO
Export from the ER is COPII-dependent. However, there is disagreement on the nature of the cargo-containing carriers that exit the ER. Two new studies from Shomron et al. (2021. J. Cell Biol.https://doi.org/10.1083/jcb.201907224) and Weigel et al. (2021. Cell. https://doi.org/10.1016/j.cell.2021.03.035) present a new model, where COPII helps to select secretory cargo but does not coat the carriers leaving the ER.
Assuntos
Vesículas Revestidas pelo Complexo de Proteína do Envoltório , Retículo Endoplasmático , Transporte Biológico , Vesículas Revestidas pelo Complexo de Proteína do Envoltório/metabolismo , Retículo Endoplasmático/metabolismo , Transporte ProteicoRESUMO
Cell migration is a fundamental biological process of key importance in health and disease. Advances in imaging techniques have paved the way to monitor cell motility. An ever-growing collection of computational tools to track cells has improved our ability to analyze moving cells. One renowned goal in the field is to provide tools that track cell movement as comprehensively and automatically as possible. However, fully automated tracking over long intervals of time is challenged by dividing cells, thus calling for a combination of automated and supervised tracking. Furthermore, after the emergence of various experimental tools to monitor cell-cycle phases, it is of relevance to integrate the monitoring of cell-cycle phases and motility. We developed CellMAPtracer, a multiplatform tracking system that achieves that goal. It can be operated as a conventional, automated tracking tool of single cells in numerous imaging applications. However, CellMAPtracer also allows adjusting tracked cells in a semiautomated supervised fashion, thereby improving the accuracy and facilitating the long-term tracking of migratory and dividing cells. CellMAPtracer is available with a user-friendly graphical interface and does not require any coding or programming skills. CellMAPtracer is compatible with two- and three-color fluorescent ubiquitination-based cell-cycle indicator (FUCCI) systems and allows the user to accurately monitor various migration parameters throughout the cell cycle, thus having great potential to facilitate new discoveries in cell biology.
Assuntos
Rastreamento de Células/métodos , Movimento Celular , Proliferação de Células , HumanosRESUMO
The growing attention toward the benefits of single-cell RNA sequencing (scRNA-seq) is leading to a myriad of computational packages for the analysis of different aspects of scRNA-seq data. For researchers without advanced programing skills, it is very challenging to combine several packages in order to perform the desired analysis in a simple and reproducible way. Here we present DIscBIO, an open-source, multi-algorithmic pipeline for easy, efficient and reproducible analysis of cellular sub-populations at the transcriptomic level. The pipeline integrates multiple scRNA-seq packages and allows biomarker discovery with decision trees and gene enrichment analysis in a network context using single-cell sequencing read counts through clustering and differential analysis. DIscBIO is freely available as an R package. It can be run either in command-line mode or through a user-friendly computational pipeline using Jupyter notebooks. We showcase all pipeline features using two scRNA-seq datasets. The first dataset consists of circulating tumor cells from patients with breast cancer. The second one is a cell cycle regulation dataset in myxoid liposarcoma. All analyses are available as notebooks that integrate in a sequential narrative R code with explanatory text and output data and images. R users can use the notebooks to understand the different steps of the pipeline and will guide them to explore their scRNA-seq data. We also provide a cloud version using Binder that allows the execution of the pipeline without the need of downloading R, Jupyter or any of the packages used by the pipeline. The cloud version can serve as a tutorial for training purposes, especially for those that are not R users or have limited programing skills. However, in order to do meaningful scRNA-seq analyses, all users will need to understand the implemented methods and their possible options and limitations.
Assuntos
Biomarcadores/análise , Biologia Computacional/métodos , RNA-Seq/métodos , Análise de Célula Única/métodos , Animais , Neoplasias da Mama/sangue , Neoplasias da Mama/diagnóstico , Neoplasias da Mama/genética , Ciclo Celular/genética , Conjuntos de Dados como Assunto , Feminino , Redes Reguladoras de Genes , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Lipossarcoma Mixoide/diagnóstico , Lipossarcoma Mixoide/genética , Camundongos , Células Neoplásicas Circulantes/patologia , Software , Peixe-ZebraRESUMO
While studies of the autophagy-related (ATG) genes in knockout models have led to an explosion of knowledge about the functions of autophagy components, the exact roles of LC3 and GABARAP family proteins (human ATG8 equivalents) are still poorly understood. A major drawback in understanding their roles is that the available interactome data has largely been acquired using overexpression systems. To overcome these limitations, we employed CRISPR/Cas9-based genome-editing to generate a panel of cells in which human ATG8 genes were tagged at their natural chromosomal locations with an N-terminal affinity epitope. This cellular resource was employed to map endogenous GABARAPL2 protein complexes using interaction proteomics. This approach identified the ER-associated protein and lipid droplet (LD) biogenesis factor ACSL3 as a stabilizing GABARAPL2-binding partner. GABARAPL2 bound ACSL3 in a manner dependent on its LC3-interacting regions, whose binding site in GABARAPL2 was required to recruit the latter to the ER. Through this interaction, the UFM1-activating enzyme UBA5 became anchored at the ER. Furthermore, ACSL3 depletion and LD induction affected the abundance of several ufmylation components and ER-phagy. Together these data allow us to define ACSL3 as a novel regulator of the enigmatic UFM1 conjugation pathway.
Assuntos
Gotículas Lipídicas , Proteínas , Autofagia , Família da Proteína 8 Relacionada à Autofagia , Humanos , Enzimas Ativadoras de UbiquitinaRESUMO
Phosphatases are a diverse family of enzymes, comprising at least 10 distinct protein folds. Like most other enzyme families, many have sequence variations that predict an impairment or loss of catalytic activity classifying them as pseudophosphatases. Research on pseudoenzymes is an emerging area of interest, with new biological functions repurposed from catalytically active relatives. Here, we provide an overview of the pseudophosphatases identified to date in all major phosphatase families. We will highlight the degeneration of the various catalytic sequence motifs and discuss the challenges associated with the experimental determination of catalytic inactivity. We will also summarize the role of pseudophosphatases in various diseases and discuss the major challenges and future directions in this field.
Assuntos
Monoéster Fosfórico Hidrolases , Proteínas/metabolismo , Animais , HumanosRESUMO
It is becoming increasingly evident that reactive oxygen species (ROS) have critical roles as "second messengers" in cell signaling. In B cells, ROS can be generated either as a byproduct of mitochondrial respiration, as a result of the endoplasmic reticulum stress response induced by high production of Igs, or by the activation of NADPH oxidase (NOX) complexes. Having previously shown that costimulation of B cells via TLR 9 and the TLR-related receptor RP105 drives maturation of human peripheral blood B cells into Ig-producing cells, we aimed to study the role of ROS generated during this vital process. To this end, the ROS levels were either reduced by the NOX inhibitor VAS2870 or by the ROS scavenger N-acetyl cysteine (NAC). We revealed that TLR9/RP105-mediated stimulation of human B cells involved a rapid activation of NOX. Moreover, VAS2870 blocked the TLR9/RP105-induced B cell activation and thereby all Ig production. Importantly, we showed that ROS targeted by NAC was selectively required for IgG but not for IgM production. The endoplasmic reticulum stress response in the TLR9/RP105-stimulated cells was higher in IgG+ than in IgG- cells and was reduced by NAC in IgG+ cells only. Of note, we revealed that substantially higher levels of IgG than IgM were produced per cell and that IgG+ cells produced significantly higher ROS levels than IgG- cells. Taken together, our results imply that NAC-targeted ROS may be particularly important for sustaining the high Ig production in IgG+ B cells.
Assuntos
Linfócitos B/imunologia , Imunoglobulina G/imunologia , Imunoglobulina M/imunologia , Espécies Reativas de Oxigênio/metabolismo , Receptores Toll-Like/imunologia , Acetilcisteína/farmacologia , Benzoxazóis/farmacologia , Humanos , Espécies Reativas de Oxigênio/antagonistas & inibidores , Triazóis/farmacologiaRESUMO
Tyrosine kinases are signaling molecules that are common to all metazoans and are involved in the regulation of many cellular processes such as proliferation and survival. While most attention has been devoted to tyrosine kinases signaling at the plasma membrane and the cytosol, very little attention has been dedicated to signaling at endomembranes. In this review, I will discuss recent evidence that we obtained on signaling of tyrosine kinases at the surface of the endoplasmic reticulum (ER), as well as in the lumen of this organelle. I will discuss how tyrosine kinase signaling might regulate ER proteostasis and the implication thereof to general cell physiology.