CD6 modulates thymocyte selection and peripheral T cell homeostasis

The CD6 glycoprotein is a lymphocyte surface receptor putatively involved in T cell development and activation. CD6 facilitates adhesion between T cells and antigen-presenting cells through its interaction with CD166/ALCAM (activated leukocyte cell adhesion molecule), and physically associates with the T cell receptor (TCR) at the center of the immunological synapse. However, its precise role during thymocyte development and peripheral T cell immune responses remains to be defined. Here, we analyze the in vivo consequences of CD6 deficiency. CD6(-/-) thymi showed a reduction in both CD4(+) and CD8(+) single-positive subsets, and double-positive thymocytes exhibited increased Ca(2+) mobilization to TCR cross-linking in vitro. Bone marrow chimera experiments revealed a T cell-autonomous selective disadvantage of CD6(-/-) T cells during development. The analysis of TCR-transgenic mice (OT-I and Marilyn) confirmed that abnormal T cell selection events occur in the absence of CD6. CD6(-/-) mice displayed increased frequencies of antigen-experienced peripheral T cells generated under certain levels of TCR signal strength or co-stimulation, such as effector/memory (CD4(+)TEM and CD8(+)TCM) and regulatory (T reg) T cells. The suppressive activity of CD6(-/-) T reg cells was diminished, and CD6(-/-) mice presented an exacerbated autoimmune response to collagen. Collectively, these data indicate that CD6 modulates the threshold for thymocyte selection and the generation and/or function of several peripheral T cell subpopulations, including T reg cells

Modulation of T lymphocite activation by ORMDL3

Genome wide association studies (GWAS) have pointed out ORMDL3 gene as a risk factor for several proinflammatory and autoimmune diseases. The protein encoded by this gene belongs to a family of transmembrane proteins of the endoplasmic reticulum involved in calcium homeostasis and cellular lipid metabolism. The driving force behind this work was the compelling idea of finding out a precise mechanism for the pathological association of this protein. This thesis explores the potential role of ORMDL3 in T lymphocytes focusing on the activation process. Thus, we have demonstrated that calcium signaling and activation of T cells are influenced by the expression levels of ORMDL3. Besides, we have shown that inherited components of our genome modify ORMDL3 expression levels and lymphocyte physiology. Finally, we have characterized the molecular complex formed by ORMDL proteins. Altogether, this work allows a better understanding of the pathophysiology associated to ORMDL3 and its linkage with the immune system.Estudis d’associació genètica ample han apuntat cap al gen ORMDL3 com a factor de risc per diverses malalties pro-inflamatòries i autoimmunes. La proteïna codificada per aquest gen pertany a una família de proteïnes transmembrana del reticle endoplàsmic involucrada en l’homeòstasi de calci i en el metabolisme lipidic cel•lular. El motiu que ens va impulsar a dur a terme aquest treball era la idea de trobar el mecanisme darrere les associacions a patologia per aquesta proteïna. Aquesta tesis explora el rol potencial d’ORMDL3 en limfòcits T, amb èmfasi al procés d’activació. Així doncs hem demostrat que la senyalització de calci i la activació de cèl•lules T es veu influenciada pels nivells d’expressió d’ORMDL3. A més hem demostrat que components del nostre genoma modifiquen els nivells d’expressió d’ORMDL3 i la fisiologia limfocitària. Per acabar hem caracteritzat el complex molecular de les proteïnes ORMDL. En conjunt, aquest treball permet una millor comprensió de la fisiopatologia associada a ORMDL3 i la seva relació amb el sistema immun

Enforced tethering elongates the cortical endoplasmic reticulum and limits store-operated calcium entry

Recruitment of STIM proteins to cortical ER (cER) domains forming membrane contact sites (MCS) mediate the store-operated Ca2+ entry (SOCE) pathway essential for human immunity. The cER is dynamically regulated by STIM and tethering proteins during SOCE, but the ultrastructural rearrangement and functional consequences of cER remodelling are unknown. Here, we express natural (E-Syt1/2) and artificial (MAPPER-S/L) protein tethers in HEK-293T cells and correlate the changes in cER length and gap distance measured by electron microscopy with ionic fluxes. Native cER cisternae extended during store depletion and remained elongated at constant ER-PM gap distance during subsequent Ca2+ elevations. Tethering proteins enhanced store-dependent cER expansion, anchoring the enlarged cER at tether-specific gap distances of 12-15nm (E-Syts) and 5-9nm (MAPPERs). Cells with artificially extended cER had reduced SOCE and reduced agonist-induced Ca2+ release. SOCE remained modulated by calmodulin and exhibited enhanced Ca2+-dependent inhibition. We propose that cER expansion mediated by ER-PM tethering at a close distance negatively regulates SOCE by confining STIM-ORAI complexes to the periphery of enlarged cER sheets, a process that might participate in the termination of store-operated Ca2+ entry

The Unfolded Protein Response: At the Intersection between Endoplasmic Reticulum Function and Mitochondrial Bioenergetics

Endoplasmic reticulum (ER) to mitochondria communication has emerged in recent years as a signaling hub regulating cellular physiology with a relevant contribution to diseases including cancer and neurodegeneration. This functional integration is exerted through discrete interorganelle structures known as mitochondria-associated membranes (MAMs). At these domains, ER/mitochondria physically associate to dynamically adjust metabolic demands and the response to stress stimuli. Here, we provide a focused overview of how the ER shapes the function of the mitochondria, giving a special emphasis to the significance of local signaling of the unfolded protein response at MAMs. The implications to cell fate control and the progression of cancer are also discussed

Extending the contacts breaks the flow

In this news and views, we discuss our recent publication where we described how ER-PM membrane contact sites (MCS) are modulated during store operated calcium entry (SOCE). We also examine why enforcing ER-PM MCS by tethering proteins does not not enhance, but rather inhibits SOCE

SARS-CoV-2 infection alkalinizes the ERGIC and lysosomes through the viroporin activity of the viral envelope protein

The coronavirus SARS-CoV-2, the agent of the deadly COVID-19 pandemic, is an enveloped virus propagating within the endocytic and secretory organelles of host mammalian cells. Enveloped viruses modify the ionic homeostasis of organelles to render their intra-luminal milieu permissive for viral entry, replication, and egress. Here, we show that infection of Vero E6 cells with the delta variant of the SARS-CoV-2 alkalinizes the endoplasmic reticulum-Golgi intermediate compartment (ERGIC) as well as lysosomes, mimicking the effect of inhibitors of vacuolar proton ATPases. We further show the envelope protein of SARS-CoV-2 accumulates in the ERGIC when expressed in mammalian cells and selectively dissipates the ERGIC pH. This viroporin is prevented by mutations of Val25 but not Asn15 within the channel pore of E. We conclude that the envelope protein acts as a proton channel in the ERGIC to mitigate the acidity of this intermediate compartment. The altered pH homeostasis of the ERGIC likely contributes to the virus fitness and pathogenicity, making the E channel an attractive drug target for the treatment of COVID-19

Calcium signaling at the endoplasmic reticulum: fine-tuning stress responses

Endoplasmic reticulum (ER) calcium signaling is implicated in a myriad of coordinated cellular processes. The ER calcium content is tightly regulated as it allows a favorable environment for protein folding, in addition to operate as a major reservoir for fast and specific release of calcium. Altered ER homeostasis impacts protein folding, activating the unfolded protein response (UPR) as a rescue mechanism to restore proteostasis. ER calcium release impacts mitochondrial metabolism and also fine-tunes the threshold to undergo apoptosis under chronic stress. The global coordination between UPR signaling and energetic demands takes place at mitochondrial associated membranes (MAMs), specialized subdomains mediating interorganelle communication. Here we discuss current models explaining the functional relationship between ER homeostasis and various cellular responses to coordinate proteostasis and metabolic maintenance.FONDECYT 1140549 3150113 FONDAP program 15150012 Millennium Institute P09-015-F European Commission R D, MSCA-RISE 734749 ALS Therapy Alliance 2014-F-059 Muscular Dystrophy Association 382453 Michael J Fox Foundation for Parkinson Research-Target Validation grant 9277 CONICYT-Brazil 441921/2016-7 US Office of Naval Research-Global (ONR-G) N62909-16-1-2003 U.S. Air Force Office of Scientific Research FA9550-16-1-0384 FONDEF 16I10223 D11E1007 ALSRP Therapeutic Idea Award AL15011

BCL-2 family: integrating stress responses at the ER to control cell demise

In the last decade, the endoplasmic reticulum (ER) has emerged as a central organelle regulating the core mitochondrial apoptosis pathway. At the ER membrane, a variety of stress signals are integrated toward determining cell fate, involving a complex cross talk between key homeostatic pathways including the unfolded protein response, autophagy, calcium signaling and mitochondrial bioenergetics. In this context, key regulators of cell death of the BCL-2 and TMBIM/BI-1 family of proteins have relevant functions as stress rheostats mediated by the formation of distinct protein complexes that regulate the switch between adaptive and proapoptotic phases under stress. Here, we overview recent advances on our molecular understanding of how the apoptotic machinery integrates stress signals toward cell fate decisions upstream of the mitochondrial gateway of death.FONDECYT 3150113 1140549 FONDAP program 15150012 Millennium Institute P09-015-F European Commission RD MSCA-RISE 734749 Michael J Fox Foundation for Parkinson's Research - Target Validation grant 9277 FONDEF ID16I10223 D11E1007 US Office of Naval Research-Global (ONR-G) N62909-16-1-2003 U.S. Air Force Office of Scientific Research FA9550-16-1-0384 ALSRP Therapeutic Idea Award AL150111 Muscular Dystrophy Association 382453 CONICYT-Brazil 441921/2016-7 CONICYT fellowshi

Non-canonical function of IRE1α determines mitochondria-associated endoplasmic reticulum composition to control calcium transfer and bioenergetics

Mitochondria-associated membranes (MAMs) are central microdomains that fine-tune bioenergetics by the local transfer of calcium from the endoplasmic reticulum to the mitochondrial matrix. Here, we report an unexpected function of the endoplasmic reticulum stress transducer IRE1α as a structural determinant of MAMs that controls mitochondrial calcium uptake. IRE1α deficiency resulted in marked alterations in mitochondrial physiology and energy metabolism under resting conditions. IRE1α determined the distribution of inositol-1,4,5-trisphosphate receptors at MAMs by operating as a scaffold. Using mutagenesis analysis, we separated the housekeeping activity of IRE1α at MAMs from its canonical role in the unfolded protein response. These observations were validated in vivo in the liver of IRE1α conditional knockout mice, revealing broad implications for cellular metabolism. Our results support an alternative function of IRE1α in orchestrating the communication between the endoplasmic reticulum and mitochondria to sustain bioenergetics.This work was funded by FONDECYT 1140549, FONDAP program 15150012, the Millennium Institute P09-015-F and the European Commission R&D MSCA-RISE 734749 (to C.H.); the Michael J. Fox Foundation for Parkinson’s Research target validation grant number 9277, FONDEF ID16I10223, FONDEF D11E1007, US Office of Naval Research-Global N62909-16-1-2003, US Air Force Office of Scientific Research FA9550-16-1-0384, ALSRP Therapeutic Idea Award AL150111, Muscular Dystrophy Association 382453, Seed grant Leading House for the Latin American Region, Switzerland and CONICYT-Brazil 441921/2016-7 (to C.H.), FONDECYT 1160332 and FONDAP15150012 (to J.C.C.); the Spanish Ministry of Economy and Competitiveness SAF2014-52228-R, Unidad de Excelencia María de Maeztu, funded by the MINECO (ref: MDM-2014-0370) and Fundació la Marató de TV3 20134030 (to R.V.); NIH NS095892 (to R.L.W.); FONDECYT 11180825 (to H.U.); FONDECYT 3150113 and EMBO ASTF 385-2016 (to A.C.-S.); FONDECYT 3140355 (to E.R.-F.); FONDECYT 3140458 and 11170291 (to F.J.); FONDECYT 3180427 (to Y.H.); FONDECYT 3190738 (to A.S.-C.); FONDECYT 11170546 and CONICYT PAI 77170091 (to C.T.-R.); R01DK113171, R01CA198103 and R01DK103185 (to R.J.K.); FONDECYT 1150766 (to F.A.C.); the Research Council KU Leuven grant OT14/101 (to G.B.); the Research Foundation – Flanders (FWO) G.0C91.14N, G.0A34.16N and the FWO Scientific Research Community “Ca2+ signaling in health, disease and therapy” W0.019.17 (to G.B.); FWO (G049817N, G076617N) and KU Leuven (C16/15/073) (to P.A.); a FWO doctorate fellowship (to M.K.); the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant 675448 (to M.L.S.); CONICYT fellowship PCHA/Doctorado Nacional/2016-21160232 (to M.G.-Q.); the George E. Hewitt Foundation for a postdoctoral fellowship (to D.E.M.); Ligue contre le Cancer (équipe labellisée); Agence National de la Recherche – Projets blancs; under the frame of E-Rare-2, the ERA-Net for Research on Rare Diseases; Association pour la recherche sur le cancer; Cancéropôle Ile-de-France; Chancelerie des universités de Paris (Legs Poix), Fondation pour la Recherche Médicale; a donation from Elior; the European Research Area Network on Cardiovascular Diseases (MINOTAUR), Gustave Roussy Odyssea, the European Union Horizon 2020 Project Oncobiome; Fondation Carrefour; High-end Foreign Expert Program in China (GDW20171100085); Institut National du Cancer; Inserm (HTE); Institut Universitaire de France; LeDucq Foundation; the LabEx Immuno-Oncology; the RHU Torino Lumière; the Seerave Foundation; the SIRIC Stratified Oncology Cell DNA Repair and Tumor Immune Elimination; and the SIRIC Cancer Research and Personalized Medicine (to G.K.)