Endoplasmic Reticulum ; genetics ; metabolism ; Plasmodium berghei ; genetics ; metabolism ; Plasmodium falciparum ; genetics ; metabolism ; Protozoan Proteins ; genetics ; metabolism

Type 2 diabetes mellitus is characterized by insulin resistance and failure of pancreatic beta-cells producing insulin. Autophagy plays a crucial role in cellular homeostasis through degradation and recycling of organelles such as mitochondria or endoplasmic reticulum (ER). Here we discussed the role of beta-cell autophagy in development of diabetes, based on our own studies using mice with beta-cell-specific deletion of Atg7 (autophagy-related 7), an important autophagy gene, and studies by others. beta-cell-specific Atg7-null mice showed reduction in beta-cell mass and pancreatic insulin content. Insulin secretory function ex vivo was also impaired, which might be related to organelle dysfunction associated with autophagy deficiency. As a result, beta-cell-specific Atg7-null mice showed hypoinsulinemia and hyperglycemia. However, diabetes never developed in those mice. Obesity and/or lipid are physiological ER stresses that can precipitate beta-cell dysfunction. Our recent studies showed that beta-cell-specific Atg7-null mice, when bred with ob/ob mice, indeed become diabetic. Thus, autophagy deficiency in beta-cells could be a precipitating factor in the progression from obesity to diabetes due to inappropriate response to obesity-induced ER stress.
Animals ; Autophagy/genetics/*physiology ; Diabetes Mellitus/genetics/*metabolism ; Endoplasmic Reticulum Stress/genetics/*physiology ; Humans ; Insulin-Secreting Cells/*metabolism

BACKGROUNDCalreticulin (CRT) is major Ca 2+ -binding chaperone mainly resident in the endoplasmic reticulum (ER) lumen. Recently, it has been shown that non-ER CRT regulates a wide array of cellular responses. We previously found that CRT was up-regulated during hypoxia/reoxygenation (H/R) and this study was aimed to investigate whether CRT nuclear translocation aggravates ER stress (ERS)-associated apoptosis during H/R injury in neonatal rat cardiomyocytes.

METHODSApoptosis rate and lactate dehydrogenase (LDH) leakage in culture medium were measured as indices of cell injury. Immunofluorescence staining showed the morphological changes of ER and intracellular translocation of CRT. Western blotting or reverse transcription polymerase chain reaction was used to detect the expression of target molecules.

RESULTSCompared with control, H/R increased apoptosis rate and LDH activity. The ER became condensed and bubbled, and CRT translocated to the nucleus. Western blotting showed up-regulation of CRT, Nrf2, activating transcription factor 4 (ATF4), CHOP and caspase-12 expression after H/R. Exogenous CRT overexpression induced by plasmid transfection before H/R increased cell apoptosis, LDH leakage, ER disorder, CRT nuclear translocation and the expression of ERS-associated molecules. However, administration of the ERS inhibitor, taurine, or CRT siRNA alleviated cell injury, ER disorder, and inhibited ERS-associated apoptosis.

CONCLUSIONSOur results indicated that during H/R stress, CRT translocation increases cell apoptosis and LDH leakage, aggravates ER disorder, up-regulates expression of nuclear transcription factors, Nrf2 and ATF4, and activates ERS-associated apoptosis.

Animals ; Apoptosis ; genetics ; physiology ; Calreticulin ; genetics ; metabolism ; Cell Hypoxia ; genetics ; physiology ; Cell Survival ; genetics ; physiology ; Cells, Cultured ; Endoplasmic Reticulum Stress ; physiology ; Myocytes, Cardiac ; cytology ; metabolism ; RNA Interference ; Rats

Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum (ER). In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethality, but its physiological role is unclear. Here, we show that Sec61β interacts directly with microtubules. Overexpression of Sec61β containing small epitope tags, but not a RFP tag, induces dramatic bundling of the ER and microtubule. A basic region in the cytosolic domain of Sec61β is critical for microtubule association. Depletion of Sec61β induces ER stress in both mammalian cells and Caenorhabditis elegans, and subsequent restoration of ER homeostasis correlates with the microtubule binding ability of Sec61β. Loss of Sec61β causes increased mobility of translocon complexes and reduced level of membrane-bound ribosomes. These results suggest that Sec61β may stabilize protein translocation by linking translocon complex to microtubule and provide insight into the physiological function of ER-microtubule interaction.
Animals ; COS Cells ; Caenorhabditis elegans Proteins ; genetics ; metabolism ; Cell Line, Tumor ; Cercopithecus aethiops ; Endoplasmic Reticulum ; metabolism ; Homeostasis ; Humans ; Microtubules ; metabolism ; SEC Translocation Channels ; deficiency ; genetics ; metabolism

OBJECTIVETo investigate the ultrastructure of myocardium and gene expression of calcium handling proteins in diabetic rat heart.

METHODSDiabetes was induced in male Sprague-Dawley rats by a single injection of alloxanm (40 mg/kg ) and the rats in control group were injected with normal saline. At the end of 2, 4, 6 weeks after the induction of diabetes, the animals were sacrificed. The expression of calcium handling proteins was detected by reverse transcription-polymerase chain reaction (RT-PCR) and actin mRNA was used as internal standard. Heart tissue at the apex was obtained for light and electron microscope study.

RESULTSAt the end of 4 and 6 weeks, cardiosomatic ratio of diabetic rats was higher than that of control. Electron microscopy revealed a spectrum of subcellular remodeling in myocardium which was characterized by damaged myofibrils and mitochondria, dilated and swollen sarcoplasmic reticulum. Expression of phospholamban mRNAs was significantly increased, but 1,4,5-trisphosphate inositol receptor type 2, ryanodine receptor type 2 mRNAs were significantly decreased compared with those in the age-matched control rats. In contrast, the expression of sarco/endoplasmic reticulum Ca(2+)-ATPase mRNAs was not affected.

CONCLUSIONIn diabetic rat heart, gene expression of calcium handling proteins was characterized by up-regulation of phospholamban and down-regulation of sarcoplasmic reticulum calcium release channel while electron microscopic analysis of myocardium revealed a spectrum of subcellular remodeling.

Animals ; Calcium ; metabolism ; Calcium Channels ; metabolism ; Calcium-Binding Proteins ; biosynthesis ; genetics ; metabolism ; Diabetes Mellitus, Experimental ; metabolism ; pathology ; Endoplasmic Reticulum ; metabolism ; ultrastructure ; Male ; Myocardium ; metabolism ; ultrastructure ; RNA, Messenger ; biosynthesis ; genetics ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Sarcoplasmic Reticulum ; metabolism ; ultrastructure

OBJECTIVETo explore the mechanisms by which HFBI fusions increase recombinant fusion protein accumulation in plants.

METHODSThe HFBI sequence from Trichoderma reesei was synthesized and two plant expression vectors for expression of green fluorescence protein (GFP) and GFP-HFBI were constructed. The vectors were inoculated in Nicotiana benthamiana plants through agroinfiltration, and the expression levels and mRNA accumulation levels of GFP in Nicotiana leaves were examined by Western blotting, ELISA and RT-PCR.

RESULTSThe HFBI fusion tag significantly enhanced the accumulation of GFP in the leaves of N. benthamiana without causing toxic effects. Endoplasmic reticulum-targeted GFP-HFBI fusion induced the formation of spherical protein particles in the plant cells.

CONCLUSIONHFBI fusions can increase the accumulation of its fusion partner in plants by forming stable protein particles, which probably shields the target protein from endogenous protease-induced degadation. HFBI fusion technology provides an alternative to improving recombinant protein expression in plants from agroinfection-compatible expression vectors.

Endoplasmic Reticulum ; Genetic Engineering ; methods ; Genetic Vectors ; Green Fluorescent Proteins ; biosynthesis ; Imidazoles ; chemistry ; Plant Leaves ; metabolism ; Plants, Genetically Modified ; genetics ; metabolism ; Recombinant Fusion Proteins ; biosynthesis ; Tobacco ; genetics ; metabolism

OBJECTIVETo explore the subcellular localization of ataxin-3 and the effect of polyglutamine (polyQ) expansion mutation on the morphology of mitochondrion, golgi apparatus and endoplasmic reticulum.

METHODSTransient transfection was employed to build cell models expressing wild-type or mutant ataxin-3 proteins. Indirect immunofluorescence was applied to identify markers of organelle membrane. The results were observed under a laser scanning confocal microscope.

RESULTSNo co-localization was observed for ataxin-3 protein and mitochondrial marker TOM20, but the percentage of cells with mitochondrial fragmentation has increased in cells expressing mutant ataxin-3 (P<0.05). No co-localization was observed for ataxin-3 protein and golgi marker GM130, and mutant ataxin-3 did not cause golgi fragmentation. Wide type and polyQ-expanded ataxin-3 both showed partial co-localization with ER marker calnexin. The latter showed more overlap with calnexin, and the overlapping signals were mostly located in the places where aggregates were situated.

CONCLUSIONPolyQ-expanded ataxin-3 protein may indirectly affect the integrity of mitochondria, but may cause no effect on the structure and functions of golgi apparatus. Endoplasmic reticulum may be another place where extended ataxin-3 protein can induce cytotoxicity in addition to the nucleus.

Ataxin-3 ; Cytoplasm ; genetics ; metabolism ; Endoplasmic Reticulum ; genetics ; metabolism ; HeLa Cells ; Humans ; Machado-Joseph Disease ; genetics ; metabolism ; Mitochondria ; genetics ; metabolism ; Nerve Tissue Proteins ; genetics ; metabolism ; Nuclear Proteins ; genetics ; metabolism ; Protein Transport ; Repressor Proteins ; genetics ; metabolism

BACKGROUNDVanishing white matter disease (VWM), a human autosomal recessive inherited leukoencephalopathy, is due to mutations in eukaryotic initiation factor 2B (eIF2B). eIF2B is responsible for the initiation of protein synthesis by its guanine nucleotide exchange factor (GEF) activity. Mutations of eIF2B impair GEF activity at different degree. Previous studies implied improperly activated unfolded protein response (UPR) and endoplasmic reticulum stress (ERS) participated in the pathogenesis of VWM. Autophagy relieves endoplasmic reticulum load by eliminating the unfolded protein. It is still unknown the effects of genotypes on the pathogenesis. In this work, UPR and autophagy flux were analyzed with different mutational types.

METHODSERS tolerance, reflected by apoptosis and cell viability, was detected in human oligodendrocyte cell line transfected with the wild type, or different mutations of p. Arg113His, p. Arg269FNx01 or p. Ser610-Asp613del in eIF2Bε. A representative UPR-PERK component of activating transcription factor 4 (ATF4) was measured under the basal condition and ERS induction. Autophagy was analyzed the flux in the presence of lysosomal inhibitors.

RESULTSThe degree of ERS tolerance varied in different genotypes. The truncated or deletion mutant showed prominent apoptosis cell viability declination after ERS induction. The most seriously damaged GEF activity of p. Arg269FNx01 group underwent spontaneous apoptosis. The truncated or deletion mutant showed elevated ATF4 under basal as well as ERS condition. Decreased expression of LC3-I and LC3-II in the mutants reflected an impaired autophagy flux, which was more obvious in the truncated or deletion mutants after ERS induction.

CONCLUSIONSGEF activities in different genotypes could influence the cell ERS tolerance as well as compensatory pathways of UPR and autophagy. Oligodendrocytes with truncated or deletion mutants showed less tolerable to ERS.

Cell Line ; Endoplasmic Reticulum Stress ; genetics ; physiology ; Eukaryotic Initiation Factor-2B ; genetics ; Humans ; Mutation ; genetics ; Oligodendroglia ; metabolism ; Unfolded Protein Response ; genetics ; physiology

OBJECTIVETo design and synthesize ribozymes targeting 138 and 218 sites of the mRNA nucleotide of mouse caspase-12, a key intermedium of ER stress mediated apoptosis, and to identify their activities through in vitro transcription and cleavage.

METHODSThe mouse caspase-12 gene fragment was obtained by RT-PCR and cloned into the PGEM-T vector under the control of T7 RNA polymerase promoter. The transcription product of the target was labeled with a-32P UTP, while ribozymes were not labeled. Ribozyme and target RNA were incubated for 90 min at 37 degree C in a reaction buffer to perform the cleavage reaction.

RESULTSIt was found that under a condition of 37 degree C, pH 7.5 and with Mg2+ in a concentration of 10 mmol/L, Rz138 and Rz218 both cleaved targets at predicted sites, and the cleavage efficiency of Rz138 was 100%.

CONCLUSIONRz138 and Rz218 prepared in vitro possess the perfect specific catalytic cleavage activity. Rz138 has excellent cleavage efficiency. It may be a promising tool to prevent ER stress induced apoptosis through catalytic cleavage of caspase-12 mRNA in vivo. It also can be used to verify whether caspase-12 is necessary in ER stress induced apoptosis.

Animals ; Base Sequence ; Caspase 12 ; genetics ; Endoplasmic Reticulum ; metabolism ; Mice ; Mice, Inbred BALB C ; Molecular Sequence Data ; Oxidative Stress ; genetics ; RNA, Catalytic ; chemistry ; genetics ; RNA, Messenger ; genetics

The endoplasmic reticulum quality control (ER-QC) is a conserved mechanism in surveillance of secreted signaling factors during cell-to-cell communication in eukaryotes. Recent data show that the ER-QC plays important roles in diverse cell-to-cell signaling processes during immune response, vegetative and reproductive development in plants. Pollen tube guidance is a precisely guided cell-cell communication process between the male and female gametophytes during plant reproduction. Recently, the female signal has been identified as small secreted peptides, but how the pollen tube responds to this signal is still unclear. In this review, we intend to summarize the role of ER-QC in plants and discuss the recent advances regarding our understanding of the mechanism of pollen tube response to the female signals.
Animals ; Endoplasmic Reticulum ; metabolism ; Humans ; Plant Cells ; metabolism ; Plant Development ; Plant Proteins ; genetics ; metabolism ; Plants ; immunology ; Pollen Tube ; cytology ; growth & development ; immunology ; metabolism ; Signal Transduction