How Does Protein Disulfide Isomerase Get Into a Thrombus?
2016; Lippincott Williams & Wilkins; Volume: 36; Issue: 6 Linguagem: Inglês
10.1161/atvbaha.116.307625
ISSN1524-4636
AutoresMeenakshi Banerjee, Sidney W. Whiteheart,
Tópico(s)Calcium signaling and nucleotide metabolism
ResumoHomeArteriosclerosis, Thrombosis, and Vascular BiologyVol. 36, No. 6How Does Protein Disulfide Isomerase Get Into a Thrombus? Free AccessEditorialPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessEditorialPDF/EPUBHow Does Protein Disulfide Isomerase Get Into a Thrombus? Meenakshi Banerjee and Sidney W. Whiteheart Meenakshi BanerjeeMeenakshi Banerjee From the Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington. and Sidney W. WhiteheartSidney W. Whiteheart From the Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington. Originally published1 Jun 2016https://doi.org/10.1161/ATVBAHA.116.307625Arteriosclerosis, Thrombosis, and Vascular Biology. 2016;36:1056–1057Numerous studies have demonstrated a role for thiol isomerases (TI), such as protein disulfide isomerase (PDI), in thrombosis.1 Using antibodies, inhibitors, inactive recombinant proteins, and transgenic animals, several groups have convincingly shown that platelet and endothelial cell enzymes contribute to normal platelet activation and deposition at vascular lesions. On the basis of these data, anti-TI therapeutics are being developed for use in humans.2 Platelets and endothelial cells contain at least 7 thioredoxin-like TIs; some of which seem to have overlapping functions.3 PDI, ERp57, and ERp5 have been studied in the most detail. For PDI, it seems to be released into the vascular microenvironment and retained via interactions with β3 integrins.4 Although important for thrombosis, it is unclear what critical substrates are modified by these enzymes or how they get into the extracellular space. To address the second question, Crescente et al5 examined how 2 TIs, PDI and ERp57, are packaged into platelets and how they are released on platelet activation.See accompanying article on page 1164Normally, TIs are present in the lumen of the endoplasmic reticulum (ER) or of other compartments of the secretory pathway. They facilitate the reshuffling of disulfide bonds in an oxidizing environment to mediate protein folding and maturation. As such, these enzymes are crucial to protein quality control and to the general trafficking of many membrane and secreted proteins. Given this important intracellular role, what are the TIs doing on the outside of an activated platelet in a growing thrombus? Data suggest that these enzymes could mediate β3 integrin activation to promote adhesion.6 Surface TIs may decrypt tissue factor thereby activating the coagulation pathway.7,8 GPIb, α2β1, thrombospondin-1, vitronectin, thrombin, antithrombin, Factor XI, and fibrin have also been considered as potential substrates1. Additionally, TIs can denitrosylate NO-modified cysteines,9 potentially reactivating inactive proteins. Despite these efforts, it is unclear whether a specific set of critical substrates or a generalized alteration in local redox environment accounts for the role of TIs in thrombosis.Our old images of platelets as simple, cell fragments containing granules, mitochondria, and some membranes are gaining more definition (Figure). Recent studies demonstrate that platelets contain many of the organelles, excepting nuclei, which are generally associated with intact cells. These organelles contribute to platelet function in ways that we are only beginning to appreciate. The dense tubular system is thought to be a calcium store and is analogous to ER.10 Golgi glycosyltransferases and sugar nucleotides have been shown to be present and active.11 Endosomal compartments,12 multivesicular bodies,13 and autophagosomes14 have all been detected in platelets. To determine where the TIs reside, Crescente et al5 did an elegant series of immunofluorescence studies of both megakaryocytes and platelets. They showed that PDI and ERp57 did not localize with classical granule markers nor with Golgi or endosomal markers. Consistently, no change in TI distribution was seen in NBEAL2−/− or Gray platelet syndrome platelets, lacking α-granules. The TIs did colocalize with SERCA3, calreticulin, and partially with calnexin, suggesting that the isomerases were present in an ER-like compartment (eg, dense tubular system). In megakaryocytes, PDI and ERp57 were found in punctate structures in the cytoplasm and then concentrated at the tips of growing proplatelets. Taken as a whole, these data argue that PDI and ERp57 are in an ER-like structure that is transferred to proplatelets during differentiation.Download figureDownload PowerPointFigure. The complexity of platelet organelles. In resting platelets, the various cargo (depicted in the legend) are present in secretory granules, endoplasmic reticulum (ER)–derived compartments, and other organelles. On activation, granule/organelle–plasma membrane fusion drives surface exposure and release of luminal cargo into the extracellular space.How are these thiol isomerases released from platelets and what does that tell us about the complexity of the platelet secretory system? To address these questions, Crescente et al5 examined PDI and ERp57 exposure on stimulated platelets. As with P-selectin, TI exposure on activated platelets was inhibited by treatment with latrunculin A suggesting a role for actin polymerization in the secretion process. Interestingly, PDI exposure was not inhibited by the loss of the tethering factor, Munc13-4. Munc13-4 is essential for dense granule release and important for α-granule release.15 It is thought to work with the small GTPase, Rab27, to bring granule and plasma membranes together and thus promote Soluble NSF-Attachment Protein Receptor protein–mediated membrane fusion.16 Does this mean Soluble NSF-Attachment Protein Receptors are not involved in PDI exteriorization? Perhaps, but there are several Soluble NSF-Attachment Protein Receptors present in platelets, not all of which may require Munc13-4 for function. Additionally, other Munc13 isoforms have been detected in platelets (T.D. Schraw and S.W. Whiteheart, unpublished data, 2004). Does this suggest that PDI release is inherently different than classical granule cargo release? Probably, and it will be interesting to determine the mechanisms of this distinct exocytosis process.This final point begs questions about what platelets can release and from where it comes (Figure). The platelet releasate contains hundreds of proteins and small molecules. Are these components coming from classical secretory granules, that is, dense and α-granules, or can activated platelets release the contents of their other organelles? From the study by Crescente et al,5 it is clear that platelets release ER contents, that is, PDI and ERp57. Other reports suggest that multivesicular bodies, Golgi, and lysosomal contents are also released.17–19 Are different Soluble NSF-Attachment Protein Receptors used for each of these membrane fusion events? Are the various secretion steps similarly regulated and is there crosstalk? More importantly, how does this mixture of granule and organelle contents (containing signaling molecules, enzymes, and substrates) affect the microenvironment of a growing thrombus? Clearly, the complex cell biology of these circulating fragments is enriching our views of what platelets can do and how they do it.Sources of FundingThis work was supported by the National Institutes of Health (NIH) HL56652 and by the American Heart Association16GRNT27620001 (to S.W. Whiteheart).DisclosuresNone.FootnotesCorrespondence to Sidney W. Whiteheart, PhD, Department of Molecular and Cellular Biochemistry, University of Kentucky, 741 S Limestone, Lexington, KY 40536. E-mail [email protected]References1. Bekendam RH, Flaumenhaft R. 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Platelets support extracellular sialylation by supplying the sugar donor substrate.J Biol Chem. 2014; 289:8742–8748. doi: 10.1074/jbc.C113.546713.CrossrefMedlineGoogle Scholar Previous Back to top Next FiguresReferencesRelatedDetailsCited By Araujo T, Zeidler J, Oliveira P, Dias M, Armelin H and Laurindo F (2017) Protein disulfide isomerase externalization in endothelial cells follows classical and unconventional routes, Free Radical Biology and Medicine, 10.1016/j.freeradbiomed.2016.12.021, 103, (199-208), Online publication date: 1-Feb-2017. June 2016Vol 36, Issue 6 Advertisement Article InformationMetrics © 2016 American Heart Association, Inc.https://doi.org/10.1161/ATVBAHA.116.307625PMID: 27225788 Originally publishedJune 1, 2016 Keywordsthrombosisplatelet activationendothelial cellsextracellular spacemegakaryocytesPDF download Advertisement
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