FKBP52 is involved in the regulation of SOCE channels in the human platelets and MEG 01 cells

AbstractImmunophilins are FK506-binding proteins that have been involved in the regulation of calcium homeostasis, either by modulating Ca2+ channels located in the plasma membrane or in the rough endoplasmic reticulum (RE). We have investigated whether immunophilins would participate in the regulation of stored-operated Ca2+ entry (SOCE) in human platelets and MEG 01. Both cell types were loaded with fura-2 for determining cytosolic calcium concentration changes ([Ca2+]c), or stimulated and fixed to evaluate the protein interaction profile by performing immunoprecipitation and western blotting. We have found that incubation of platelets with FK506 increases Ca2+ mobilization. Thapsigargin (TG)-evoked, Thr-evoked SOCE and TG-evoked Mn2+ entry resulted in significant reduction by treatment of platelets with immunophilin antagonists. We confirmed by immunoprecipitation that immunophilins interact with transient receptor potential channel 1 (TRPC1) and Orai1 in human platelets. FK506 and rapamycin reduced the association between TRPC1 and Orai1 with FK506 binding protein (52) (FKBP52) in human platelets, and between TRPC1 and the type II IP3R, which association is known to be crucial for the maintenance of SOCE in human platelets. FKBP52 role in SOCE activation was confirmed by silencing FKBP52 using SiRNA FKBP52 in MEG 01 as demonstrated by single cell configuration imaging technique. TRPC1 silencing and depletion of cell of TRPC1 and FKBP52 simultaneously, impair activation of SOCE evoked by TG in MEG 01. Finally, in MEG 01 incubated with FK506 we observed a reduction in TRPC1/FKBP52 coupling, and similarly, FKBP52 silencing reduced the association between IP3R type II and TRPC1 during SOCE. All together, these results demonstrate that immunophilins participate in the regulation of SOCE in human platelets

Two-pore channel 2 (TPC2) modulates store-operated Ca2+ entry

AbstractTwo-pore channels (TPCs) are NAADP-sensitive receptor channels that conduct Ca2+ efflux from the intracellular stores. Discharge of the internal Ca2+ pools results in the activation of store-operated Ca2+ entry (SOCE); however, the role of TPCs in the modulation of SOCE remains unexplored. Mammalian cells express three TPCs: TPC1, TPC2 and TPC3, a pseudogene in humans. Here we report that MEG01 and HEK293 cells endogenously express TPC1 and TPC2. Silencing TPC2 expression results in attenuation of the rate and extent of thapsigargin (TG)-evoked SOCE both in MEG01 and HEK293 cells, without having any effect on the ability of cells to accumulate Ca2+ into the TG-sensitive stores. Similarly, silencing of native TPC2 expression reduced thrombin-induced Ca2+ entry in MEG01 cells. In contrast, silencing of TPC1 expression was without effect either on TG or thrombin-stimulated Ca2+ entry both in MEG01 and HEK293 cells. Biotinylation analysis revealed that TPC1 and TPC2 are expressed in internal membranes. Finally, co-immunoprecipitation experiments indicated that endogenously expressed TPC2, but not TPC1, associates with STIM1 and Orai1, but not with TRPC1, in MEG01 cells with depleted intracellular Ca2+ stores, but not in resting cells. These results provide strong evidence for the modulation of SOCE by TPC2 involving de novo association between TPC2 and STIM1, as well as Orai1, in human cells

EFHB is a Novel Cytosolic Ca2+ Sensor That Modulates STIM1-SARAF Interaction

Background/aims: STIM1 and Orai1 are the key components of store-operated Ca2+ entry (SOCE). Among the proteins involved in the regulation of SOCE, SARAF prevents spontaneous activation of SOCE and modulates STIM1 function. Methods: Cytosolic Ca2+ mobilization was estimated in fura-2-loaded cells using an epifluorescence inverted microscope. STIM1 interaction with Orai1, EFHB (EF-hand domain family member B, also known as CFAP21) and SARAF was detected by immunoprecipitation followed by Western blotting using specific antibodies. The involvement of EFHB in the translocation of NFAT to the nucleus was detected by confocal microscopy. Results: Here, we report the identification of EFHB as a new SOCE regulator. EFHB interacts with STIM1 upon store depletion and dissociates through a Ca2+-dependent mechanism. RNAi-mediated silencing as well as overexpression studies revealed that EFHB plays a relevant role in the interaction of STIM1 and Orai1 upon store depletion, the activation of SOCE and NFAT translocation from the cytosol to the nucleus. Silencing EFHB expression abolished the dissociation of SARAF from STIM1, which indicates that EFHB might play an important role in the dynamic interaction between both proteins, which is relevant for the activation of Orai1 channels upon Ca2+ store depletion and their subsequent modulation via slow Ca2+-dependent inactivation. Conclusion: Our results indicate that EFHB is a new SOCE regulator that modulates STIM1-SARAF interaction.MINECO BFU2013-45564-C2-1-P/2-P, BFU2016-74932-C2-1-P/2-P, BFU2016-74932-C2-1-PJunta de Extremadura-FEDER (Fondo Europeo de Desarrollo Regional Grants) IB16046, GR18061Junta de Extremadura-FEDER European Union (EU) IB16046Ministerio Economía y Competitividad, España IJCI-2015-25665MINECO Grant BFU2016-74932-C2-1-

Dynamic interaction of SARAF with STIM1 and orai1 to modulate store-operated calcium entry

El flujo de Ca2+ por almacenado por canales de Ca2+ es un mecanismo importante para la homeostasis intracelular de Ca2+ y la función celular. Aquí presentamos la evidencia de la interacción dinámica entre el factor regulador asociado SOCE (SARAF), STIM1 y Orai1. La expresión atenuada SARAF y la interacción SOCE STIM1-Orai1 en células expresan endógenamente a STIM1 y Orai1 mientras RNAi está condicionada por silenciamiento de SARAF induciendo efectos opuestos. SARAF menoscaba la asociación entre Orai1 y la activación de Orai1 del pequeño fragmento de STIM1 expresada en la STIM1-L115-401NG deficiente de células. En tratamiento de la celda con agonistas o thapsigargin fisiológico resulta en asociación directa de SARAF con Orai1. La interacción de ESTIMI1 independiente de SARAF con Orai1 conduce a la activación de este canal. Las células expresan endógenamente STIM1 y el agotamiento del almacenado de Orai1, Ca2+ conduce a la disociación de SARAF de STIM1 a los 30 segundos después del tratamiento con thapsigargin, paralelo al aumento de SARAF en la interacción con Orai1, seguido por reinteracción con STIM1 y la disociación desde Orai1. La expresión de SARAF y Orai1 o la supresión de diversos N-terminal de mutantes de Orai1 no altera la interacción de SARAF-Orai1; sin embargo, la expresión de eliminación de C-terminal y los mutantes de Orai1 bloquean la C-terminal de Orai1 y menoscaban la interacción con SARAF. Estas observaciones sugieren que SARAF ejerce un papel positivo inicial en la activación de SOCE seguida por la facilitación del SCDI de Orai1.Ca2+ influx by store-operated Ca2+ channels is a major mechanism for intracellular Ca2+ homeostasis and cellular function. Here we present evidence for the dynamic interaction between the SOCE associated regulatory factor (SARAF), STIM1 and Orai1. SARAF overexpression attenuated SOCE and the STIM1-Orai1 interaction in cells endogenously expressing STIM1 and Orai1 while RNAi-mediated SARAF silencing induced opposite effects. SARAF impaired the association between Orai1 and the Orai1-activating small fragment of STIM1 co-expressed in the STIM1-deficient NG115-401L cells. Cell treatment with thapsigargin or physiological agonists results in direct association of SARAF with Orai1. STIM1-independent interaction of SARAF with Orai1 leads to activation of this channel. In cells endogenously expressing STIM1 and Orai1, Ca2+ store depletion leads to dissociation of SARAF withSTIM1 approximately 30s after treatment with thapsigargin, which paralleled the increase in SARAFOrai1 interaction, followed by reinteraction with STIM1 and dissociation from Orai1. Co-expression of SARAF and either Orai1 or various N-terminal deletion Orai1 mutants did not alter SARAF-Orai1 interaction; however, expression of C-terminal deletion Orai1 mutants or blockade of the C-terminus of Orai1 impair the interaction with SARAF. These observations suggest that SARAF exerts an initial positive role in the activation of SOCE followed by the facilitation of SCDI of Orai1.• Ministerio de Economía y Competitividad. Becas BFU2013-45564-C2-1-P, BFU2013-45564-C2-2-P, BFU2011-24365 and RD12-0043-0016 (RETICEF) • Ministerio de Economía y Competitividad. Programa Juan de la Cierva para José Javier López Barba • Ministerio de Economía y Competitividad. Beca BES-2011-043356 para Letizia Albarrán Alonso • Junta de Extremadura y Fondos FEDERpeerReviewe

Store-Operated Calcium Entry in Breast Cancer Cells Is Insensitive to Orai1 and STIM1 N-Linked Glycosylation.

N-linked glycosylation is a post-translational modification that affects protein function, structure, and interaction with other proteins. The store-operated Ca2+ entry (SOCE) core proteins, Orai1 and STIM1, exhibit N-glycosylation consensus motifs. Abnormal SOCE has been associated to a number of disorders, including cancer, and alterations in Orai1 glycosylation have been related to cancer invasiveness and metastasis. Here we show that treatment of non-tumoral breast epithelial cells with tunicamycin attenuates SOCE. Meanwhile, tunicamycin was without effect on SOCE in luminal MCF7 and triple negative breast cancer (TNBC) MDA-MB-231 cells. Ca2+ imaging experiments revealed that expression of the glycosylation-deficient Orai1 mutant (Orai1N223A) did not alter SOCE in MCF10A, MCF7 and MDA-MB-231 cells. However, expression of the non-glycosylable STIM1 mutant (STIM1N131/171Q) significantly attenuated SOCE in MCF10A cells but was without effect in SOCE in MCF7 and MDA-MB-231 cells. In non-tumoral cells impairment of STIM1 N-linked glycosylation attenuated thapsigargin (TG)-induced caspase-3 activation while in breast cancer cells, which exhibit a smaller caspase-3 activity in response to TG, expression of the non-glycosylable STIM1 mutant (STIM1N131/171Q) was without effect on TG-evoked caspase-3 activation. Summarizing, STIM1 N-linked glycosylation is essential for full SOCE activation in non-tumoral breast epithelial cells; by contrast, SOCE in breast cancer MCF7 and MDA-MB-231 cells is insensitive to Orai1 and STIM1 N-linked glycosylation, and this event might participate in the development of apoptosis resistance

EFHB is a novel cytosolic Ca²+ sensor that modulates STIM1-SARAF interaction

FUNDAMENTOS/OBJETIVOS: STIM1 y Orai1 son los componentes clave de la entrada de Ca2+ en la tienda (SOCE). Entre las proteínas que participan en la regulación de la SOCE, la SARAF previene la activación espontánea de la SOCE y modula la función de STIM1. MÉTODOS: Se estimó la movilización de Ca2+ citosólico en células cargadas de fura-2 usando un microscopio invertido de epifluorescencia. La interacción de STIM1 con Orai1, EFHB (miembro de la familia B del dominio de la mano EF, también conocido como CFAP21) y SARAF se detectó mediante inmunoprecipitación seguida de Western blotting utilizando anticuerpos específicos. La participación de EFHB en la translocación de NFAT al núcleo se detectó mediante microscopía confocal. RESULTADOS: Aquí reportamos la identificación del EFHB como un nuevo regulador SOCE. El EFHB interactúa con el STIM1 al agotarse el almacenamiento y se disocia a través de un mecanismo dependiente de Ca2+-. El silenciamiento mediado por el ARNi así como los estudios de sobreexpresión revelaron que el EFHB juega un papel relevante en la interacción de STIM1 y Orai1 al agotarse las reservas, la activación de la translocación de SOCE y NFAT del citosol al núcleo. El silenciamiento de la expresión de la EFHB suprimió la disociación de la SARAF de la STIM1, lo que indica que la EFHB podría desempeñar un papel importante en la interacción dinámica entre ambas proteínas, lo que es pertinente para la activación de los canales de Orai1 al agotarse el almacenamiento de Ca2+ y su posterior modulación mediante la inactivación lenta dependiente del Ca2+. CONCLUSIÓN: Nuestros resultados indican que el EFHB es un nuevo regulador SOCE que modula la interacción STIM1-SARAF.BACKGROUND/AIMS: STIM1 and Orai1 are the key components of store-operated Ca2+ entry (SOCE). Among the proteins involved in the regulation of SOCE, SARAF prevents spontaneous activation of SOCE and modulates STIM1 function. METHODS: Cytosolic Ca2+ mobilization was estimated in fura-2-loaded cells using an epifluorescence inverted microscope. STIM1 interaction with Orai1, EFHB (EF-hand domain family member B, also known as CFAP21) and SARAF was detected by immunoprecipitation followed by Western blotting using specific antibodies. The involvement of EFHB in the translocation of NFAT to the nucleus was detected by confocal microscopy. RESULTS: Here, we report the identification of EFHB as a new SOCE regulator. EFHB interacts with STIM1 upon store depletion and dissociates through a Ca2+- dependent mechanism. RNAi-mediated silencing as well as overexpression studies revealed that EFHB plays a relevant role in the interaction of STIM1 and Orai1 upon store depletion, the activation of SOCE and NFAT translocation from the cytosol to the nucleus. Silencing EFHB expression abolished the dissociation of SARAF from STIM1, which indicates that EFHB might play an important role in the dynamic interaction between both proteins, which is relevant for the activation of Orai1 channels upon Ca2+ store depletion and their subsequent modulation via slow Ca2+-dependent inactivation. CONCLUSION: Our results indicate that EFHB is a new SOCE regulator that modulates STIM1-SARAF interaction.• Ministerio de Economía y Competitividad. Contrato Juan de la Cierva IJCI-2015-25665, para Isaac Jardín Polo • Junta de Extremadura y Fondos FEDER. Contrato IB16046, para José Javier López Barba • Ministerio de Economía y Competitividad. Subvención BFU2016-74932-C2-1-P, para Letizia Albarrán Alonso • Ministerio de Economía y Competitividad. Subvenciones Subvenciones BFU2013-45564-C2-1-P/2-P y BFU2016-74932-C2-1-P/2-P • Junta de Extremadura y Fondos FEDER. Subvenciones IB16046 y GR18061peerReviewe

EFHB is a Novel Cytosolic Ca2+ Sensor That Modulates STIM1-SARAF Interaction

Background/Aims: STIM1 and Orai1 are the key components of store-operated Ca2+ entry (SOCE). Among the proteins involved in the regulation of SOCE, SARAF prevents spontaneous activation of SOCE and modulates STIM1 function. Methods: Cytosolic Ca2+ mobilization was estimated in fura-2-loaded cells using an epifluorescence inverted microscope. STIM1 interaction with Orai1, EFHB (EF-hand domain family member B, also known as CFAP21) and SARAF was detected by immunoprecipitation followed by Western blotting using specific antibodies. The involvement of EFHB in the translocation of NFAT to the nucleus was detected by confocal microscopy. Results: Here, we report the identification of EFHB as a new SOCE regulator. EFHB interacts with STIM1 upon store depletion and dissociates through a Ca2+-dependent mechanism. RNAi-mediated silencing as well as overexpression studies revealed that EFHB plays a relevant role in the interaction of STIM1 and Orai1 upon store depletion, the activation of SOCE and NFAT translocation from the cytosol to the nucleus. Silencing EFHB expression abolished the dissociation of SARAF from STIM1, which indicates that EFHB might play an important role in the dynamic interaction between both proteins, which is relevant for the activation of Orai1 channels upon Ca2+ store depletion and their subsequent modulation via slow Ca2+-dependent inactivation. Conclusion: Our results indicate that EFHB is a new SOCE regulator that modulates STIM1-SARAF interaction

Generierung und Charakterisierung von Stromal Interaction Molecule 2 (STIM2)-defizienten Mäusen

An increase in cytosolic Ca2+ levels ([Ca2+]i) is a key event that occurs downstream of many signaling cascades in response to an external stimulus and regulates a wide range of cellular processes, including platelet activation. Eukaryotic cells increase their basal [Ca2+]i allowing extracellular Ca2+ influx into the cell, which involves different mechanisms. Store-operated Ca2+ entry (SOCE) is considered the main mechanism of extracellular Ca2+ influx in electrically non-excitable cells and platelets, and comprises an initial Ca2+ depletion from intracellular Ca2+ stores prior to activation of extracellular Ca2+ influx. Although the close relation between Ca2+ release from intracellular stores and extracellular Ca2+ influx was clear, the nature of the signal that linked both events remained elusive until 2005, when Stromal Interaction Molecule 1 (STIM1) was identified as an endoplasmic reticulum (ER) Ca2+ sensor essential for inositol (1,4,5)-trisphosphate (IP3)-mediated SOCE in vitro. However, the function of its homologue STIM2 in Ca2+ homeostasis was in general unknown. Therefore, mice lacking STIM2 (Stim2-/-) were generated in this work to study initially STIM2 function in platelets and in cells of the immune system. Stim2-/- mice developed normally in size and weight to adulthood and were fertile. However, for unknown reasons, they started to die spontaneously at the age of 8 weeks. Unexpectedly, Stim2-/- mice did not show relevant differences in platelets, revealing that STIM2 function is not essential in these cells. However, STIM2 seems to be involved in mammary gland development during pregnancy and is essential for mammary gland function during lactation. CD4+ T cells lacking STIM2 showed decreased SOCE. Our data suggest that STIM2 has a very specific function in the immune system and is involved in Experimental Autoimmune Encephalomyelitis (EAE) at early stages of the disease progression. Stim2-/- neurons were also defective in SOCE. Surprisingly, our results evidenced that STIM2 participates in mechanisms of neuronal damage after ischemic events in brain. This is the first time that the involvement of SOCE in ischemic neuronal damage has been reported. This finding may serve as a basis for the development of novel neuroprotective agents for the treatment of ischemic stroke, and possibly other neurodegenerative disorders in which disturbances in cellular Ca2+ homeostasis are considered a major pathophysiological component.Der Anstieg des cytosolischen Ca2+-Spiegels ([Ca2+]i) ist ein Schlüsselereignis, das vielen Signalkaskaden, durch extrazellulären Stimulus ausgelöst werden, nachgeschalten ist, und eine große Reihe zellulärer Prozesse reguliert, z.B. die Aktivierung von Blutplättchen. Eukaryotische Zellen erhöhen ihren basalen ([Ca2+]i) durch Einstrom von extrazellulärem Ca2+ in die Zelle hinein, was durch verschiedene Mechanismen geschehen kann. Store-operated Ca2+-entry (SOCE), wird als der Hauptmechanismus für den Einstrom von extrazellulärem Ca2+ in nicht elektrisch-erregbaren Zellen sowie Plättchen angesehen und beinhaltet einen initialen Ca2+-Ausstrom aus intrazellulären Speichern der dem Ca2+-Einstrom aus der Extrazellulärraum vorrausgeht. Obwohl die Beziehung zwischen Ca2+-Ausstrom aus intrazellulären Speichern und extrazellulärem Ca2+-Einstrom über die Plasmamembran viele Jahre bekannt war, so blieb doch das beide Ereignisse verknüpfende Element unbekannt. Im Jahre 2005 jedoch wurde Stromal Interaction Molecule 1 (STIM1) als Ca2+-Sensor des endoplasmatischen Retikulums (ER) und als essentieller Bestandteil für inositol(1,4,5)-triphosphat (IP3)-vermittelten SOCE in vitro identifiziert. Die Funktion seines Homologs, STIM2, in der Ca2+ Homeostase blieb jedoch unklar. Aus diesem Grund generierten wir STIM2-defiziente (Stim2-/-) Mäuse um die Funktion dieses Proteins in Blutplättchen und Immunzellen untersuchen zu können. Bis zum Erwachsenenalter entwickelten sich Stim2-/- Mäuse normal in Bezug auf Größe und Gewicht und waren fertil. Jedoch sterben die Tiere spontan aus unbekannten Gründen, beginnend ab einem Alter von 8 Wochen. Unerwarteter Weise, zeigten Stim2-/- Mäuse keine maßgeblichen Funktionsunterschiede in Plättchen, was eine essentielle Funktion von STIM2 in diesen Zellen ausschließt. Jedoch scheint STIM2 in die Entwicklung der Brustdrüsen während der Schwangerschaft involviert und essentiell für die Brustdrüsenfunktion während der Säugephase zu sein. Darüberhinaus zeigten STIM2 defiziente CD4+ T-Zellen einen verminderten SOCE. Weiter deuten unsere Daten auf eine spezifische Funktion von STIM2 im Immunsystem hin, mit einem Einfluss auf die frühen Phasen und das Fortschreiten der Experimentellen Autoimmun-Enzephalomyelitis (EAE). Stim2-/- Neuronen wiesen ebenso wie CD4+ T-Zellen einen gestörten SOCE auf. Desweiteren belegen unsere Ergebnisse, dass STIM2 überrascherweise an den Neuronen zerstörenden Mechanismen nach ischämischen Ereignissen des Gehirns mitwirkt. Dies ist die erste Studie, die von einer Beteiligung von SOCEan ischämischen neuronalen Schäden berichtet. Diese Entdeckungen können vielleicht als Basis für die Entwicklung neuer neuroprotektiver Medikamente bei ischämischen Schlaganfall dienen - und möglicherweise auch bei anderen neurodegenerativen Erkrankungen, bei denen Störungen der zellulären Ca2+ Homöostase als hauptsächliche pathophysologische Komponente angesehen werden

FKBP25 and FKBP38 regulate non-capacitative calcium entry through TRPC6

AbstractNon-capacitative calcium entry (NCCE) contributes to cell activation in response to the occupation of G protein-coupled membrane receptors. Thrombin administration to platelets evokes the synthesis of diacylglycerol downstream of PAR receptor activation. Diacylglycerol evokes NCCE through activating TRPC3 and TRPC6 in human platelets. Although it is known that immunophilins interact with TRPCs, the role of immunophilins in the regulation of NCCE remains unknown. Platelet incubation with FK506, an immunophilin antagonist, reduced OAG-evoked NCCE in a concentration-dependent manner, an effect that was independent on the inactivation of calcineurin (CaN). FK506 was unable to reduce NCCE evoked by OAG in platelets from TRPC6−/− mice. In HEK-293 cells overexpressing TRPC6, currents through TRPC6 were altered in the presence of FK506. We have found interaction between FKBP38 and other FKBPs, like FKBP25, FKBP12, and FKBP52 that were not affected by FK506, as well as with calmodulin (CaM). FK506 modified the pattern of association between FKBP25 and TRPCs as well as impaired OAG-evoked TRPC3 and TRPC6 coupling in both human and mouse platelets. By performing biotinylation experiments we have elucidated that FKBP25 and FKBP38 might be found at different cellular location, the plasma membrane and the already described intracellular locations. Finally, FKBP25 and FKBP38 silencing significantly inhibits OAG-evoked NCCE in MEG-01 and HEK293 cells, while overexpression of FKBP38 does not modify NCCE in HEK293 cells. All together, these findings provide strong evidence for a role of immunophilins, including FKBP25 and FKBP38, in NCCE mediated by TRPC6