Extensive endoplasmic reticulum: a distinguishing feature of auxin-producing plant cells

Résumé Le cytoplasme des cellules végétales capables de synthétiser l'auxine est caractérisé par l'abondance du réticulum endoplasmique. Les cellules dont la croissance est stimulée par de hautes concentrations de cette hormone contiennent beaucoup moins de réticulum endoplasmique. D'où l'hypothèse que le lieu de synthèse de l'auxine (dans les cellules capables de cette synthèse) est peut-être le réticulum endoplasmique.

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This work was begun at Manhattan College, Bronx, New York, supported by USPHS grant No. CA 06955, the Anna Fuller fund, and the Christine Sonntag Foundation. The work was continued at the Boyce Thompson Institute, Yonkers, New York, and completed at the Wistar Institute with support from USPHS grant No. CA 10815.

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I am grateful to Dr.G. Hagen for theNicotiana tissues, Dr.J. Lippincott for theP. savastanoi cultures and to Mrs.B. di Gregorio andE. Manasse for competent technical assistance.     

Role of <Emphasis Type="Italic">N</Emphasis>-linked polymannose oligosaccharides in targeting glycoproteins for endoplasmic reticulum-associated degradation

Misfolded or incompletely assembled multisubunit glycoproteins undergo endoplasmic reticulum-associated degradation (ERAD) regulated in large measure by their N-linked polymannose oligosaccharides. In this quality control system lectin interaction with Glc₃Man₉GlcNAc₂ glycans after trimming with endoplasmic reticulum (ER) -glucosidases and -mannosidases sorts out persistently unfolded glycoproteins for N-deglycosylation and proteolytic degradation. Monoglucosylated (Glc₁Man₉GlcNAc₂) glycoproteins take part in the calnexin/calreticulin glucosylation-deglucosylation cycle, while the Man₈GlcNAc₂ isomer B product of ER mannosidase I interacts with EDEM. Proteasomal degradation requires retrotranslocation into the cytosol through a Sec61 channel and deglycosylation by peptide: N-glycosidase (PNGase); in alternate models both PNGase and proteasomes may be either free in the cytosol or ER membrane-imbedded/attached. Numerous proteins appear to undergo nonproteasomal degradation in which deglycosylation and proteolysis take place in the ER lumen. The released free oligosaccharides (OS) are transported to the cytosol as OS-GlcNAc₂ along with similar components produced by the hydrolytic action of the oligosaccharyltransferase, where they together with OS from the proteasomal pathway are trimmed to Man₅GlcNAc₁ by the action of cytosolic endo--N-acetylglucosaminidase and -mannosidase before entering the lysosomes. Some misfolded glycoproteins can recycle between the ER, intermediate and Golgi compartments, where they are further processed before ERAD. Moreover, properly folded glycoproteins with mannose-trimmed glycans can be deglucosylated in the Golgi by endomannosidase, thereby releasing calreticulin and permitting formation of complex OS. A number of regulatory controls have been described, including the glucosidase-glucosyltransferase shuttle, which controls the level of Glc₃Man₉GlcNAc₂-P-P-Dol, and the unfolded protein response, which enhances synthesis of components of the quality control system.Received 26 January 2004; accepted 25 February 2004     

Similar paracrystals of endoplasmic reticulum in the photoemitters and the photoreceptors of scale-worms

Summary Paracrystals of tubular endoplasmic reticulum are the characteristic of the luminous cells in the elytra of polynoïd worms, and they are the sources of luminescence as well as of fluorescence. Structurally similar paracrystals are now found to be the main constituent of the lens in the eyes of all the Aphroditidae.     

From the endoplasmic reticulum to the plasma membrane: mechanisms of CFTR folding and trafficking

CFTR biogenesis starts with its co-translational insertion into the membrane of endoplasmic reticulum and folding of the cytosolic domains, towards the acquisition of a fully folded compact native structure. Efficiency of this process is assessed by the ER quality control system that allows the exit of folded proteins but targets unfolded/misfolded CFTR to degradation. If allowed to leave the ER, CFTR is modified at the Golgi and reaches the post-Golgi compartments to be delivered to the plasma membrane where it functions as a cAMP- and phosphorylation-regulated chloride/bicarbonate channel. CFTR residence at the membrane is a balance of membrane delivery, endocytosis, and recycling. Several adaptors, motor, and scaffold proteins contribute to the regulation of CFTR stability and are involved in continuously assessing its structure through peripheral quality control systems. Regulation of CFTR biogenesis and traffic (and its dysregulation by mutations, such as the most common F508del) determine its overall activity and thus contribute to the fine modulation of chloride secretion and hydration of epithelial surfaces. This review covers old and recent knowledge on CFTR folding and trafficking from its synthesis to the regulation of its stability at the plasma membrane and highlights how several of these steps can be modulated to promote the rescue of mutant CFTR.     

Role of the nuclear membrane in smooth endoplasmic reticulum formation in white rat pinealocytes

Résumé La glande pinéale du rat blanc est étudiée ici au microscope électronique. L'association observée entre les vésicules agranulaires et les «blebs» de la membrane nucléaire est un argument en faveur de la théorie selon laquelle l'origine du reticulum endoplasmique est à rechercher dans la membrane nucléaire.     

Menadione-induced apoptosis and the degradation of lamin-like proteins in tobacco protoplasts

Detection of stereotypic hallmarks of apoptosis during cell death induced by menadione, including DNA laddering and the formation of apoptotic bodies, is reported. Comet assay and the TdT-mediated dUTP nick end labelling (TUNEL) procedure were also performed to detect DNA fragmentation. Inhibition of DNA fragmentation by Ac-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) and phenylmethylsulfosyl (PMSF) implicated the involvement of caspase-like proteases in menadione-induced apoptosis in plants. We further studied the cleavage of lamin-like proteins during apoptosis in menadione-treated tobacco protoplasts. In animals, it has been reported that the solubilization of nuclear lamina and lamin degradation occurs during apoptotic cell death. However, little is known about the fate of lamins in apoptotic plant cells. Our study provided evidence that lamin-like proteins degraded into 35-kDa fragments in tobacco protoplasts induced by menadione, and this preceded DNA fragmentation. The results thus indicated that proteolytic cleavage of nuclear lamins was also conserved in programmed cell death in plants. Received 16 November 1998; received after revision 21 December 1998; accepted 23 December 1998     

Proteomic interaction profiling reveals KIFC1 as a factor involved in early targeting of F508del-CFTR to degradation

Misfolded F508del-CFTR, the main molecular cause of the recessive disorder cystic fibrosis, is recognized by the endoplasmic reticulum (ER) quality control (ERQC) resulting in its retention and early degradation. The ERQC mechanisms rely mainly on molecular chaperones and on sorting motifs, whose presence and exposure determine CFTR retention or exit through the secretory pathway. Arginine-framed tripeptides (AFTs) are ER retention motifs shown to modulate CFTR retention. However, the interactions and regulatory pathways involved in this process are still largely unknown. Here, we used proteomic interaction profiling and global bioinformatic analysis to identify factors that interact differentially with F508del-CFTR and F508del-CFTR without AFTs (F508del-4RK-CFTR) as putative regulators of this specific ERQC checkpoint. Using LC–MS/MS, we identified kinesin family member C1 (KIFC1) as a stronger interactor with F508del-CFTR versus F508del-4RK-CFTR. We further validated this interaction showing that decreasing KIFC1 levels or activity stabilizes the immature form of F508del-CFTR by reducing its degradation. We conclude that the current approach is able to identify novel putative therapeutic targets that can be ultimately used to the benefit of CF patients.     

Immunophilins: for the love of proteins

Immunophilins are chaperones that may also exhibit peptidylprolyl isomerase (PPIase) activity. This review summarizes our knowledge of the two largest families of immunophilins, namely cyclophilin and FK506-binding protein, and a novel chimeric dual-family immunophilin, named FK506- and cyclosporin-binding protein (FCBP). The larger members of each family are modular in nature, consisting of multiple PPIase and/or protein-protein interaction domains. Despite the apparent difference in their sequence and three-dimensional structure, the three families encode similar enzymatic and biological functions. Recent studies have revealed that many immunophilins possess a chaperone function independent of PPIase activity. Knockout animal studies have confirmed multiple essential roles of immunophilins in physiology and development. An immunophilin is indeed a natural ‘protein-philin’ (Greek ‘philin’ = friend) that interacts with proteins to guide their proper folding and assembly. Received: 7 May 2006; received after revision 3 July 2006; accepted 24 August 2006     

Isolation of a cytochrome of the antimycin a sensitive pathway for DPNH oxidation

Zusammenfassung Ein neues Cytochrom ist aus Schweineleber isoliert worden. Es wird durch DPNH-Cytochrom-c-Reduktase reduziert. Antimycin A hemmt diese Reaktion, die nur in Gegenwart des Slater-Faktors abläuft.Es ist wahrscheinlich, dass dieses Cytochrom in die Elektronentransportreihe, und zwar zwischen Reduktase und Cytochrom c, eingeschaltet ist.     

Short-term effects of colcemid on the rapid axonal transport of proteins in the optic pathway of chick embryos

Riassunto La somministrazione endoculare di piccole dosi di Colcemid in embrioni di pollo al 13° e al 18° giorno di incubazione diminuisce la sintesi proteica nella retina. Pur in misura diversa, i due farmaci bloccano il trasporto assonico di proteine dalle cellule gangliari retiniche al tetto ottico. Anche nell'embrione quindi il trasporto assonico dipende dalla integrità dei microtubuli neuronali.

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This work was supported by Consiglio Nazionale delle Ricerche (C.N.R.), Rome, Italy.     

Serotonin is localized in endothelial cells of coronary arteries and released during hypoxia: a possible new mechanism for hypoxia-induced vasodilatation of the rat heart

In this report we demonstrate the immunocytochemical localization of serotonin in endothelial cells of rat coronary vessels and a significant increase in the release of serotonin into the perfusate of Langendorff rat heart preparations during hypoxia. It is suggested that serotonin, localized in endothelial cells, is released during hypoxia and could provide part of a pathophysiological mechanism for vasodilatation to protect the heart from damage due to hypoxia.