scholarly journals The calcium-dependent ribonuclease XendoU promotes ER network formation through local RNA degradation

2014 ◽  
Vol 207 (1) ◽  
pp. 41-57 ◽  
Author(s):  
Dianne S. Schwarz ◽  
Michael D. Blower
Keyword(s):  
Network Formation ◽  
Cytosolic Calcium ◽  
Rna Degradation ◽  
Dependent Manner ◽  
Calcium Dependent ◽  
Culture Cells ◽  
Egg Extract ◽  
Nuclear Envelope Assembly ◽  
Rnase Treatment ◽  
Calcium Lead

How cells shape and remodel organelles in response to cellular signals is a poorly understood process. Using Xenopus laevis egg extract, we found that increases in cytosolic calcium lead to the activation of an endogenous ribonuclease, XendoU. A fraction of XendoU localizes to the endoplasmic reticulum (ER) and is required for nuclear envelope assembly and ER network formation in a catalysis-dependent manner. Using a purified vesicle fusion assay, we show that XendoU functions on the surface of ER membranes to promote RNA cleavage and ribonucleoprotein (RNP) removal. Additionally, RNA removal from the surface of vesicles by RNase treatment leads to increased ER network formation. Using human tissue culture cells, we found that hEndoU localizes to the ER, where it promotes the formation of ER tubules in a catalysis-dependent manner. Together, these results demonstrate that calcium-activated removal of RNA from membranes by XendoU promotes and refines ER remodeling and the formation of tubular ER.

scholarly journals Regulation of Cellular Calcium in Vestibular Supporting Cells by Otopetrin 1

2010 ◽  
Vol 104 (6) ◽  
pp. 3439-3450 ◽  
Author(s):  
Euysoo Kim ◽  
Krzysztof L. Hyrc ◽  
Judith Speck ◽  
Yunxia W. Lundberg ◽  
Felipe T. Salles ◽  
...  
Keyword(s):  
Culture System ◽  
Calcium Concentration ◽  
Vestibular Function ◽  
Cytosolic Calcium ◽  
Extracellular Calcium ◽  
Dependent Manner ◽  
Supporting Cells ◽  
Calcium Dependent ◽  
Organ Culture System ◽  
High Concentrations

Otopetrin 1 (OTOP1) is a multitransmembrane domain protein, which is essential for mineralization of otoconia, the calcium carbonate biominerals required for vestibular function, and the normal sensation of gravity. The mechanism driving mineralization of otoconia is poorly understood, but it has been proposed that supporting cells and a mechanism to maintain high concentrations of calcium are critical. Using Otop1 knockout mice and a utricular epithelial organ culture system, we show that OTOP1 is expressed at the apex of supporting cells and functions to increase cytosolic calcium in response to purinergic agonists, such as adenosine 5′-triphosphate (ATP). This is achieved by blocking mobilization of calcium from intracellular stores in an extracellular calcium-dependent manner and by mediating influx of extracellular calcium. These data support a model in which OTOP1 acts as a sensor of the extracellular calcium concentration near supporting cells and responds to ATP in the endolymph to increase intracellular calcium levels during otoconia mineralization.

scholarly journals Type IIa RPTPs and Glycans: Roles in Axon Regeneration and Synaptogenesis

2021 ◽  
Vol 22 (11) ◽  
pp. 5524
Author(s):  
Kazuma Sakamoto ◽  
Tomoya Ozaki ◽  
Yuji Suzuki ◽  
Kenji Kadomatsu
Keyword(s):  
Heparan Sulfate ◽  
Network Formation ◽  
Synapse Formation ◽  
Axon Regeneration ◽  
Transmembrane Protein ◽  
Inhibitory Synapses ◽  
Dependent Manner ◽  
Axon Terminals ◽  
Axon Extension ◽  
Receptor Tyrosine Phosphatases

Type IIa receptor tyrosine phosphatases (RPTPs) play pivotal roles in neuronal network formation. It is emerging that the interactions of RPTPs with glycans, i.e., chondroitin sulfate (CS) and heparan sulfate (HS), are critical for their functions. We highlight here the significance of these interactions in axon regeneration and synaptogenesis. For example, PTPσ, a member of type IIa RPTPs, on axon terminals is monomerized and activated by the extracellular CS deposited in neural injuries, dephosphorylates cortactin, disrupts autophagy flux, and consequently inhibits axon regeneration. In contrast, HS induces PTPσ oligomerization, suppresses PTPσ phosphatase activity, and promotes axon regeneration. PTPσ also serves as an organizer of excitatory synapses. PTPσ and neurexin bind one another on presynapses and further bind to postsynaptic leucine-rich repeat transmembrane protein 4 (LRRTM4). Neurexin is now known as a heparan sulfate proteoglycan (HSPG), and its HS is essential for the binding between these three molecules. Another HSPG, glypican 4, binds to presynaptic PTPσ and postsynaptic LRRTM4 in an HS-dependent manner. Type IIa RPTPs are also involved in the formation of excitatory and inhibitory synapses by heterophilic binding to a variety of postsynaptic partners. We also discuss the important issue of possible mechanisms coordinating axon extension and synapse formation.

scholarly journals Ca2+-Dependent Protein Kinase 6 Enhances KAT2 Shaker Channel Activity in Arabidopsis thaliana

2021 ◽  
Vol 22 (4) ◽  
pp. 1596
Author(s):  
Elsa Ronzier ◽  
Claire Corratgé-Faillie ◽  
Frédéric Sanchez ◽  
Christian Brière ◽  
Tou Cheu Xiong
Keyword(s):  
Arabidopsis Thaliana ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Physical Interaction ◽  
Fluorescence Lifetime Imaging ◽  
Dependent Manner ◽  
In Planta ◽  
Knock Out ◽  
Calcium Dependent ◽  
Dependent Protein

Post-translational regulations of Shaker-like voltage-gated K+ channels were reported to be essential for rapid responses to environmental stresses in plants. In particular, it has been shown that calcium-dependent protein kinases (CPKs) regulate Shaker channels in plants. Here, the focus was on KAT2, a Shaker channel cloned in the model plant Arabidopsis thaliana, where is it expressed namely in the vascular tissues of leaves. After co-expression of KAT2 with AtCPK6 in Xenopuslaevis oocytes, voltage-clamp recordings demonstrated that AtCPK6 stimulates the activity of KAT2 in a calcium-dependent manner. A physical interaction between these two proteins has also been shown by Förster resonance energy transfer by fluorescence lifetime imaging (FRET-FLIM). Peptide array assays support that AtCPK6 phosphorylates KAT2 at several positions, also in a calcium-dependent manner. Finally, K+ fluorescence imaging in planta suggests that K+ distribution is impaired in kat2 knock-out mutant leaves. We propose that the AtCPK6/KAT2 couple plays a role in the homeostasis of K+ distribution in leaves.

scholarly journals The EF-Hand Ca2+-binding Protein p22 Plays a Role in Microtubule and Endoplasmic Reticulum Organization and Dynamics with Distinct Ca2+-binding Requirements

2004 ◽  
Vol 15 (2) ◽  
pp. 481-496 ◽  
Author(s):  
Josefa Andrade ◽  
Hu Zhao ◽  
Brian Titus ◽  
Sandra Timm Pearce ◽  
Margarida Barroso
Keyword(s):  
Endoplasmic Reticulum ◽  
Conformational Changes ◽  
Membrane Trafficking ◽  
Secretory Pathway ◽  
Network Formation ◽  
Binding Protein ◽  
Dependent Manner ◽  
Microtubule Depolymerization ◽  
Independent Manner ◽  
Ef Hand

We have reported that p22, an N-myristoylated EF-hand Ca2+-binding protein, associates with microtubules and plays a role in membrane trafficking. Here, we show that p22 also associates with membranes of the early secretory pathway membranes, in particular endoplasmic reticulum (ER). On binding of Ca2+, p22's ability to associate with membranes increases in an N-myristoylation-dependent manner, which is suggestive of a nonclassical Ca2+-myristoyl switch mechanism. To address the intracellular functions of p22, a digitonin-based “bulk microinjection” assay was developed to load cells with anti-p22, wild-type, or mutant p22 proteins. Antibodies against a p22 peptide induce microtubule depolymerization and ER fragmentation; this antibody-mediated effect is overcome by preincubation with the respective p22 peptide. In contrast, N-myristoylated p22 induces the formation of microtubule bundles, the accumulation of ER structures along the bundles as well as an increase in ER network formation. An N-myristoylated Ca2+-binding p22 mutant, which is unable to undergo Ca2+-mediated conformational changes, induces microtubule bundling and accumulation of ER structures along the bundles but does not increase ER network formation. Together, these data strongly suggest that p22 modulates the organization and dynamics of microtubule cytoskeleton in a Ca2+-independent manner and affects ER network assembly in a Ca2+-dependent manner.

scholarly journals The calcium-dependent ATP-Mg/Pi mitochondrial carrier is a target of glucose-induced calcium signalling in Saccharomyces cerevisiae

2005 ◽  
Vol 392 (3) ◽  
pp. 537-544 ◽  
Author(s):  
Santiago Cavero ◽  
Javier Traba ◽  
Araceli Del Arco ◽  
Jorgina Satrústegui
Keyword(s):  
Calcium Binding ◽  
Mitochondrial Protein ◽  
Calcium Signalling ◽  
Cytosolic Calcium ◽  
Calcium Signal ◽  
Transport Activity ◽  
Wild Type ◽  
Binding Motifs ◽  
Mitochondrial Carrier ◽  
Calcium Dependent

Sal1p is a mitochondrial protein that belongs to the SCaMC (short calcium-binding mitochondrial carrier) subfamily of mitochondrial carriers. The presence of calcium-binding motifs facing the extramitochondrial space allows the regulation of the transport activity of these carriers by cytosolic calcium and provides a new mechanism to transduce calcium signals in mitochondria without the requirement of calcium entry in the organelle. We have studied its transport activity, finding that it is a carboxyatractyloside-resistant ATP-Mg carrier. Mitochondria from a disruption mutant of SAL1 have a 50% reduction in the uptake of ATP. We have also found a clear stimulation of ATP-transport activity by calcium, with an S0.5 of approx. 30 μM. Our results also suggest that Sal1p is a target of the glucose-induced calcium signal which is non-essential in wild-type cells, but becomes essential for transport of ATP into mitochondria in yeast lacking ADP/ATP translocases.

Direct effect of parathyroid hormone on insulin secretion from pancreatic islets

1990 ◽  
Vol 258 (6) ◽  
pp. E975-E984 ◽  
Author(s):  
G. Z. Fadda ◽  
M. Akmal ◽  
L. G. Lipson ◽  
S. G. Massry
Keyword(s):  
Insulin Secretion ◽  
Parathyroid Hormone ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Direct Effect ◽  
Indirect Evidence ◽  
Cytosolic Calcium ◽  
Dependent Manner ◽  
Stimulation Of

Indirect evidence indicates that parathyroid hormone (PTH) interacts with pancreatic islets and modulates their insulin secretion. This property of PTH has been implicated in the genesis of impaired insulin release in chronic renal failure. We examined the direct effect of PTH-(1-84) and PTH-(1-34) on insulin release using in vitro static incubation and dynamic perifusion of pancreatic islets from normal rats. Both moieties of the hormone stimulated in a dose-dependent manner glucose-induced insulin release but higher doses inhibited glucose-induced insulin release. This action of PTH was modulated by the calcium concentration in the media. The stimulatory effect of PTH was abolished by its inactivation and blocked by its antagonist [Tyr-34]bPTH-(7-34)NH2. PTH also augmented phorbol ester (TPA)-induced insulin release, stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation by pancreatic islets, and significantly increased (+50 +/- 2.7%, P less than 0.01) their cytosolic calcium. Verapamil inhibited the stimulatory effect of PTH on insulin release. The data show that 1) pancreatic islets are a PTH target and may have PTH receptors, 2) stimulation of glucose-induced insulin release by PTH is mediated by a rise in cytosolic calcium, 3) stimulation of cAMP production by PTH and a potential indirect activation of protein kinase C by PTH may also contribute to the stimulatory effect on glucose-induced insulin release, and 4) this action of PTH requires calcium in incubation or perifusion media.

Interaction of the smooth endoplasmic reticulum and mitochondria

2006 ◽  
Vol 34 (3) ◽  
pp. 370-373 ◽  
Author(s):  
J.G. Goetz ◽  
I.R. Nabi
Keyword(s):  
Endoplasmic Reticulum ◽  
Smooth Endoplasmic Reticulum ◽  
Close Association ◽  
Cytosolic Calcium ◽  
Functional Roles ◽  
Calcium Dependent ◽  
Motility Factor ◽  
Calcium Sequestration ◽  
Multiple Domains ◽  
The Relationship

The ER (endoplasmic reticulum) is composed of multiple domains including the nuclear envelope, ribosome-studded rough ER and the SER (smooth ER). The SER can also be functionally segregated into domains that regulate ER–Golgi traffic (transitional ER), ERAD (ER-associated degradation), sterol and lipid biosynthesis and calcium sequestration. The last two, as well as apoptosis, are critically regulated by the close association of the SER with mitochondria. Studies with AMFR (autocrine motility factor receptor) have defined an SER domain whose integrity and mitochondrial association can be modulated by ilimaquinone as well as by free cytosolic calcium levels in the normal physiological range. AMFR is an E3 ubiquitin ligase that targets its ligand directly to the SER via a caveolae/raft-dependent pathway. In the present review, we will address the relationship between the calcium-dependent morphology and mitochondrial association of the SER and its various functional roles in the cell.

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