Introduction: Whole blood transfusions are indicated for the resuscitation of patients with hemorrhagic trauma. In Sweden, whole blood is stored for 14 days at 4°C. If possible, refrigerated blood is rewarmed to 37°C before transfusion to avoid hypothermia. Platelets contribute to hemostasis and can be activated with several pathways. During storage, shedding of platelet surface receptors takes place. Further research on how platelet storage in whole blood and rewarming before transfusion affect platelets is needed. Aim: The aim was to study how storage in whole blood and rewarming to 37°C affect platelet function, platelet activatability, and changes in platelet surface receptors. Method: Whole blood from two healthy donors was stored for 14 days. During these 14 days, two blood samples were taken on day 0, before and after leukocyte reducing filtration, 1, 3, 7, and 14. One of the two blood samples from each whole blood product was tested at room temperature and the other was rewarmed to 37°C. The blood samples were mixed with antibodies and platelet agonists and analyzed on a flow cytometer. The blood samples were also analyzed on a cell counter. Results: This study shows distinct changes in platelet spontaneous activation, platelet count, and platelet receptor shedding by increased storage time in cold-stored whole blood and even more with rewarming to 37°C. Conclusion: This study shows that during storage, spontaneous platelet activation and shedding of GPIb and GPIIb increases while platelet count decreases. All these factors are likely affecting the platelet function and hemostatic function negatively.

Cytotoxic T lymphocytes (CTL) kill virally infected and tumourigenic cells via the regulated secretion of specialised secretory lysosomes. These secretory lysosomes contain cytolytic effector molecules, such as perforin and granzymes, which are able to induce apoptosis in target cells. Secretion occurs at the contact point between the CTL and its target, in a highly structured region termed the immunological synapse (IS). Upon formation of the IS, CTL undergo polarisation of their microtubule cytoskeleton and movement of the microtubule organising centre (MTOC) to the IS. Secretory lysosomes are then able to polarise along microtubules, fuse with the plasma membrane and deliver their effector molecules to the IS. The Adaptor Protein 3 complex (AP-3) sorts transmembrane proteins to lysosomes and deficiency in AP-3 results in missorting of proteins from the lysosomal to plasma membrane. CTL from AP-3 deficient patients, who suffer from Hermansky-Pudlak Syndrome Type 2 (HPS2), show reduced killing of target cells. This thesis describes two new patients with HPS2, both with homozygous mutations in the AP3B1 gene, which codes for the β3A subunit of the AP-3 complex. CTL from the new HPS2 patients show reduced cytotoxicity, which is shown here to be due to impaired secretory lysosome polarisation towards the IS. This impairment is common to HPS2 CTL, but varies between patients. In order to determine differences between HPS2 and wild type CTL, the localisation of a range of lysosomal, cytolytic, transmembrane, inhibitory and activation marker proteins is examined. This shows that in HPS2 CTL, LAMP1, CD63 and CD9 are potential AP-3 cargos. In addition, a possible effect on the key lytic effector perforin is identified. Preliminary experiments to allow proteomic comparison of HPS2 and wild type CTL are also presented. Further investigation of these results will help to shed light on the mechanisms involved in secretory lysosome polarisation in CTL.

O prion celular (PrPc) é uma glicoproteína ligada à membrana plasmática por uma âncora de GPI (glycosylphosphatidylinositol). A sua isoforma anormal (PrPsc) é uma molécula infecciosa que causa várias doenças neurodegenerativas em mamíferos. A etiologia dessas doenças está associada a uma mudança conformacional pós-traducional de PrPc que ocorre após sua internalização (Prusiner, 1998). Na tentativa de desvendar as funções fisiológicas de PrPc, nosso grupo tem identificado e caracterizado as interações celulares que PrPc participa. A primeira delas é a interação entre PrPc e STI1 (Stress Inducible Protein 1). Essa interação transduz sinalização por cAMP e PKA levando a neuroproteção contra morte celular programada (Chiarini e cols, 2002; Zanata e cols, 2002). A segunda é a interação específica que existe entre PrPc e as proteínas da matriz extracelular, laminina e vitronectina, contribuindo para os processos neuronais, tais como crescimento, manutenção (Graner e cols., 2000 a e b) e regeneração dos neuritos (Hajj e cols., submetido), além da formação de memória de curta e longa duração (Coitinho e cols., submetido). Na primeira parte deste trabalho, procuramos investigar os genes regulados pelos sinais resultantes dessas interações e também pela remoção de PrPc usando a técnica de \"differential display\'\' RT-PCR. Na segunda parte do trabalho, caracterizamos que a interação PrPc - laminina é capaz de induzir uma sinalização transitória de cálcio, a qual ocorre mesmo na ausência de cálcio do meio extracelular. PrPc é uma molécula que cicla continuamente entre a membrana plasmática e os compartimentos intracelulares. Estudos recentes têm correlacionado o processo de internalização de PrPc com alguns dos seus papeis fisiológicos, tais como, homeostase de Cu2 + (Brown, 2001 ), interação com receptor de laminina (Gauczynski e cols, 2001) e até na conversão de PrPc para PrPsc (McKinley e cols, 1991; Arnold e cols, 1995). Portanto, na terceira parte deste trabalho, caracterizamos a localização e o tráfego celular de PrPc mostrando que PrPc está localizado na membrana plasmática e em compartimentos intracelulares e que trafega pelo Golgi, membrana plasmática, endossomos iniciais e de reciclagem. Foram mapeados ainda domínios na região amino-terminal responsáveis pela internalização de PrPc e na região carboxi-terminal como participantes da via secretora. Este trabalho contribuiu para o esclarecimento de alguns eventos biológicos relacionados à sinalização e ao tráfego de PrPc. Estes achados são de grande importância para a determinação das funções celulares de PrPc e ainda dos mecanismos envolvidos com as doenças relacionadas com esta molécula. / The cellular prion protein (PrPc) is a glycoprotein anchored to the plasma membrane by GPI (Glycosyl-phosphatidylinositol). Its abnormal isoform (PrPsc) is the infectious protein responsible for several neurodegenerative diseases. The main etiology of the prion diseases is related to conformational changes in the PrPc molecule, which occur after its internalization (Prusiner, 1998). In order to elucidate the physiological functions of PrPc, our group identified and characterized interactions between PrPc and other cellular molecules. The first is the interaction between PrPc and STI 1 (Stress Inducible Protein 1). This interaction has an important role in the neuroprotection against apoptosis through cAMP and PKA signaling (Chiarini et al., 2002; Zanata et al., 2002). PrPc also interacts with proteins of the extracellular matrix such as laminin and vitronetin. These interactions contribute for neurite outgrowth, maintenance and regeneration (Graner et al., 2000 a and b; Hajj et al., submitted) and also in memory formation (Coitinho et al., submitted). In the first part of this work we have applied the differential dysplay RTPCR technique in order to identify genes that are regulated by PrPc - STI 1 interaction and also by the deletion of PrPc. In the second part we have demonstrated that PrPc-laminin interaction induces transient calcium signaling in neuronal cells, which occurs even in the absence of extracellular calcium. PrPc cycles continuously between the plasma membrane and intracellular compartments. This mechanism is associated with some of the physiological function of PrPc, such as Cu2+ homeostasis (Brown, 2001 ), interaction with laminin receptor (Gauczynski et al., 2001 ), and PrPc conversion into PrPsc (McKinley et al., 1991; Arnold et al., 1995). Thus, in the third part of this project, we have characterized the PrPc localization at the cell surface and in intracellular compartments. The protein trafficking through Golgi apparatus, plasma membrane, early and recycling endosomes was also defined. Moreover, we have determinated that N-terminus PrPc domain is responsible for its internalization while C-terminus participates in PrPc delivery. Therefore, this work has contributed to elucidate biological events related to the cell signaling and trafficking of PrPc, which are important for the characterization of PrPc physiological functions and to understand the pathological mechanisms related to this molecule.

O prion celular (PrPc) é uma glicoproteína ligada à membrana plasmática por uma âncora de GPI (glycosylphosphatidylinositol). A sua isoforma anormal (PrPsc) é uma molécula infecciosa que causa várias doenças neurodegenerativas em mamíferos. A etiologia dessas doenças está associada a uma mudança conformacional pós-traducional de PrPc que ocorre após sua internalização (Prusiner, 1998). Na tentativa de desvendar as funções fisiológicas de PrPc, nosso grupo tem identificado e caracterizado as interações celulares que PrPc participa. A primeira delas é a interação entre PrPc e STI1 (Stress Inducible Protein 1). Essa interação transduz sinalização por cAMP e PKA levando a neuroproteção contra morte celular programada (Chiarini e cols, 2002; Zanata e cols, 2002). A segunda é a interação específica que existe entre PrPc e as proteínas da matriz extracelular, laminina e vitronectina, contribuindo para os processos neuronais, tais como crescimento, manutenção (Graner e cols., 2000 a e b) e regeneração dos neuritos (Hajj e cols., submetido), além da formação de memória de curta e longa duração (Coitinho e cols., submetido). Na primeira parte deste trabalho, procuramos investigar os genes regulados pelos sinais resultantes dessas interações e também pela remoção de PrPc usando a técnica de \"differential display\'\' RT-PCR. Na segunda parte do trabalho, caracterizamos que a interação PrPc - laminina é capaz de induzir uma sinalização transitória de cálcio, a qual ocorre mesmo na ausência de cálcio do meio extracelular. PrPc é uma molécula que cicla continuamente entre a membrana plasmática e os compartimentos intracelulares. Estudos recentes têm correlacionado o processo de internalização de PrPc com alguns dos seus papeis fisiológicos, tais como, homeostase de Cu2 + (Brown, 2001 ), interação com receptor de laminina (Gauczynski e cols, 2001) e até na conversão de PrPc para PrPsc (McKinley e cols, 1991; Arnold e cols, 1995). Portanto, na terceira parte deste trabalho, caracterizamos a localização e o tráfego celular de PrPc mostrando que PrPc está localizado na membrana plasmática e em compartimentos intracelulares e que trafega pelo Golgi, membrana plasmática, endossomos iniciais e de reciclagem. Foram mapeados ainda domínios na região amino-terminal responsáveis pela internalização de PrPc e na região carboxi-terminal como participantes da via secretora. Este trabalho contribuiu para o esclarecimento de alguns eventos biológicos relacionados à sinalização e ao tráfego de PrPc. Estes achados são de grande importância para a determinação das funções celulares de PrPc e ainda dos mecanismos envolvidos com as doenças relacionadas com esta molécula. / The cellular prion protein (PrPc) is a glycoprotein anchored to the plasma membrane by GPI (Glycosyl-phosphatidylinositol). Its abnormal isoform (PrPsc) is the infectious protein responsible for several neurodegenerative diseases. The main etiology of the prion diseases is related to conformational changes in the PrPc molecule, which occur after its internalization (Prusiner, 1998). In order to elucidate the physiological functions of PrPc, our group identified and characterized interactions between PrPc and other cellular molecules. The first is the interaction between PrPc and STI 1 (Stress Inducible Protein 1). This interaction has an important role in the neuroprotection against apoptosis through cAMP and PKA signaling (Chiarini et al., 2002; Zanata et al., 2002). PrPc also interacts with proteins of the extracellular matrix such as laminin and vitronetin. These interactions contribute for neurite outgrowth, maintenance and regeneration (Graner et al., 2000 a and b; Hajj et al., submitted) and also in memory formation (Coitinho et al., submitted). In the first part of this work we have applied the differential dysplay RTPCR technique in order to identify genes that are regulated by PrPc - STI 1 interaction and also by the deletion of PrPc. In the second part we have demonstrated that PrPc-laminin interaction induces transient calcium signaling in neuronal cells, which occurs even in the absence of extracellular calcium. PrPc cycles continuously between the plasma membrane and intracellular compartments. This mechanism is associated with some of the physiological function of PrPc, such as Cu2+ homeostasis (Brown, 2001 ), interaction with laminin receptor (Gauczynski et al., 2001 ), and PrPc conversion into PrPsc (McKinley et al., 1991; Arnold et al., 1995). Thus, in the third part of this project, we have characterized the PrPc localization at the cell surface and in intracellular compartments. The protein trafficking through Golgi apparatus, plasma membrane, early and recycling endosomes was also defined. Moreover, we have determinated that N-terminus PrPc domain is responsible for its internalization while C-terminus participates in PrPc delivery. Therefore, this work has contributed to elucidate biological events related to the cell signaling and trafficking of PrPc, which are important for the characterization of PrPc physiological functions and to understand the pathological mechanisms related to this molecule.

Wang Ying. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 124-135). / Abstracts in English and Chinese. / Acknowledgements / Abstract / 摘要 / Table of contents / List of figures / List of tables / List of abbreviations / CHAPTER / Chapter 1. --- Introduction / Chapter 1.1 --- Background of SARS and epidemiology / Chapter 1.2 --- SARS symptoms and infected regions / Chapter 1.3 --- SARS virus / Chapter 1.4 --- Treatment for SARS at present / Chapter 1.5 --- Vaccine development is a more effective way to fight against SARS / Chapter 1.6 --- Vaccine candidates / Chapter 1.6.1 --- Truncated S protein as a vaccine candidate / Chapter 1.6.2 --- Full-length N protein as a vaccine candidate / Chapter 1.7 --- E.coli expression system / Chapter 1.8 --- Baculovirus expression system / Chapter 1.8.1 --- Characteristics of baculovirus / Chapter 1.8.2 --- Infection cycle of baculovirus / Chapter 1.8.3 --- Control of viral gene expression in virus-infected cells / Chapter 1.8.4 --- Merits of baculovirus expression system / Chapter 1.9 --- Aim of study / Chapter 2. --- "Bacterial expression and purification of rS1-1000(E), rS401-1000(E) and rN(E)" / Chapter 2.1 --- Introduction / Chapter 2.2 --- Materials / Chapter 2.2.1 --- Reagents for bacterial culture / Chapter 2.2.2 --- Reagents for agarose gel electrophoresis / Chapter 2.2.3 --- 2'-deoxyribonucleoside 5'-triphosphate (dNTP) mix for polymerase chain reaction (PCR) / Chapter 2.2.4 --- Sonication buffer / Chapter 2.2.5 --- Reagents for immobilized metal affinity chromatography (IMAC) purification / Chapter 2.2.6 --- Reagents for gel filtration chromatography / Chapter 2.2.7 --- Reagents for sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) / Chapter 2.2.8 --- Reagents for Western blotting / Chapter 2.3 --- Methods / Chapter 2.3.1 --- General techniques in molecular cloning / Chapter 2.3.2 --- "PCR amplification of the S1-400,S401-1000" / Chapter 2.3.3 --- Construction of clone pET-S 1-400 and PET-s401-1000 / Chapter 2.3.4 --- Construction of clone pAC-N / Chapter 2.3.5 --- Expression / Chapter 2.3.6 --- Inclusion bodies preparation / Chapter 2.3.7 --- Inclusion bodies solubilization using urea / Chapter 2.3.8 --- Protein refolding by rapid dilution and dialysis / Chapter 2.3.9 --- Purification of recombinant protein by nickel ion chelating Sepharose fast flow column (IMAC) / Chapter 2.3.10 --- Gel filtration chromatography for further purification / Chapter 2.3.11 --- Bradford assay for the protein concentration analysis / Chapter 2.3.12 --- Protein analysis / Chapter 2.4 --- Results / Chapter 2.4.1 --- SDS-PAGE analysis of the expressed proteins / Chapter 2.4.2 --- Western blot analysis of the bacterial cell lysate / Chapter 2.4.3 --- Protein purification by IMAC / Chapter 2.4.4 --- Purification of rS401-1000(E) by gel filtration / Chapter 2.4.5 --- Determination of production yield of recombinant fusion proteins / Chapter 2.5 --- Discussion / Chapter 2.5.1 --- Expression vector selected for rS1-400(E) and rS401-1000(E) expression / Chapter 2.5.2 --- Protein expression in E.coli / Chapter 2.5.3 --- Purification process / Chapter 3. --- Baculovirus expression and purification of rS401-1000(ACN) and rN(BMN) protein / Chapter 3.1 --- Introduction / Chapter 3.2 --- Materials / Chapter 3.2.1 --- Reagents for insect cell culture and virus work / Chapter 3.3 --- Methods / Chapter 3.3.1 --- "PCR amplification of N and cloning of S401-1000, N genes into the transfer vector pVL1393" / Chapter 3.3.2 --- Cloning of S401-1000 into transfer vector pFastBac HT B / Chapter 3.3.3 --- Virus works / Chapter 3.3.4 --- Identification of recombinant BmNPV or AcMNPV / Chapter 3.3.5 --- Manipulation of silkworm / Chapter 3.3.6 --- Mouse immunization for polyclonal antibody against rN(E) protein / Chapter 3.4 --- Results / Chapter 3.4.1 --- Expression of rN(BMN) in baculovirus / Chapter 3.4.2 --- Expression of rS401-1000(BMN) and rS401-1000(ACN) in baculovirus / Chapter 3.5 --- Discussion / Chapter 3.5.1 --- The expression level of rN(BMN) in both in vitro and invivo / Chapter 3.5.2 --- The rS401-1000(ACN) protein expression level in vitro / Chapter 3.5.3 --- Failure in generating rS401-1000(BMN) / Chapter 3.5.4 --- Purification process of rN(BMN) by IMAC / Chapter 4. --- "Characterization of recombinant rS1-400(E), rN(E), rN(BMN), rS401_1000(E) and rS401-1000(ACN)" / Chapter 4.1 --- Introduction / Chapter 4.2 --- Materials / Chapter 4.2.1 --- Reagents for enzyme-linked immunosorbent assay (ELISA) / Chapter 4.2.2 --- Reagents for purification of human IgG / Chapter 4.2.3 --- Source and identity of Immune sera / Chapter 4.3 --- Methods / Chapter 4.3.1 --- ELISA / Chapter 4.3.2 --- Purification process of human IgG / Chapter 4.4 --- Results / Chapter 4.4.1 --- Validation of Immune sera using SARS viral lysate / Chapter 4.4.2 --- Immunoreactivities of rS1-400(E) and rN(E) against pooled patients sera and normal human serum / Chapter 4.4.3 --- Immunoreactivity comparison of rN(E) and rN(BMN) / Chapter 4.4.4 --- Comparison of the immunoreactivities of rS401-1000(E) and rS401-1000(ACN) / Chapter 4.4.5 --- Immunoreactivity of SARS related proteins against Anti-SARS Antibody (Equine) / Chapter 4.5 --- Discussion / Chapter 4.5.1 --- Comparison of the immunoreactivities of SARS related proteins expressed in the present study / References

Cystinuria is defined as an inherited disorder characterized by increased urinary excretion of cystine and the dibasic amino acids arginine, lysine and ornithine. The only clinical manifestation of cystinuria is renal cystine stone formation due to the low solubility of cystine in the urine. Cystinuria can be attributed to mutations in the SLC3A1 and SLC7A9 genes in the majority of all cases and it has been a common expectation that molecular genetic studies of cystinuria would aid in understanding of the varying clinical outcome seen in the disease. Besides human, the disease has been most extensively studied in the domestic dog. The present study was undertaken to investigate the molecular genetic basis of cystinuria in patients from Sweden and to correlate genetic findings with phenotypes produced regarding cystine and dibasic amino acid excretion. Further, attempts were made to elucidate the molecular genetics of cystinuria in the dog. The entire coding sequences of the SLC3A1 and SLC7A9 genes were analysed by means of SSCA and DNA sequencing in 53 cystinuria patients and genetic findings were related to urinary excretion of cystine and dibasic amino acids in a subset of the patient group. We detected a total number of 22 different mutations in the SLC3A1 and SLC7A9 genes, 18 of which were described for the first time. We have found a probable genetic cause of cystinuria in approximately 74 % of our patients and a possible contribution to the disease in another 19 %. Mutations in the SLC3A1 gene is the major cause of cystinuria in our group, with only a minor contribution of SLC7A9 mutations. The group of patients presenting SLC3A1 mutations in a heterozygous state or lacking mutations in both genes had higher values of total urinary cystine and dibasic amino acids compared to patients homozygous for SLC3A1 mutations. The reason for this discrepancy remains unclear, but the possible impact of medical treatment with sulfhydryl compounds on total cystine values was ruled out. Sequencing of the full-length canine SLC7A9 cDNA was accomplished using the RACE technology and results from mutation analyses of SLC7A9 and SLC3A1 in cystinuric dogs showed that only two out of 13 dogs have mutations with possible impact on protein function in these genes. DNA sequencing was used for all exons of both genes in the dog, and in human cystinuria patients, all samples lacking mutations or showing heterozygosity after SSCA screening were sequenced in both genes as well. This implies that all point mutations present have been detected, but the possibility of mutations escaping PCR based methods as well as mutations in regulatory parts of the SLC3A1 and SLC7A9 genes remains in cases lacking a full molecular genetic explanation of the disease. Finally, clinical and genetic data from our study of cystinuria both in man and dog exemplifies that manifestation and clinical severity of cystinuria is not determined by genetic alterations in the SLC3A1 and SLC7A9 alone. Environmental factors, congenital malformations and modulating genetic factors are all possible contributors to the clinical outcome of cystinuria.

Thesis (Ph. D.)--University of Missouri--Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 139-154).

Diss. (sammanfattning) Linköping : Linköpings universitet, 2007. / Härtill 4 uppsatser.

Allergic asthma is characterized by airway hyperresponsiveness, inflammation, and a cellular infiltrate dominated by eosinophils. Numerous epidemiological studies have related the exacerbation of allergic asthma with an increase in ambient inhalable particulate matter from air pollutants. This is because inhalable particles efficiently deliver airborne allergens deep into the airways, where they can aggravate allergic asthma symptoms. However, the cellular mechanisms by which inhalable particulate allergens (pAgs) potentiate asthmatic symptoms remain unknown, in part because most in vivo and in vitro studies exploring the pathogenesis of allergic asthma use soluble allergens (sAgs). Using a mouse model of allergic asthma, we found that, compared with their sAg counterparts, pAgs triggered markedly heightened airway hyperresponsiveness and pulmonary eosinophilia in allergen-sensitized mice. Mast cells (MCs) were implicated in this divergent response, as the differences in airway inflammatory responses provoked by the physical nature of the allergens were attenuated in MC-deficient mice. The pAgs were found to mediate MC-dependent responses by enhancing retention of pAg/IgE/FcεRI complexes within lipid raft–enriched, CD63(+) endocytic compartments, which prolonged IgE/FcεRI-initiated signaling and resulted in heightened cytokine responses. These results reveal how the physical attributes of allergens can co-opt MC endocytic circuitry and signaling responses to aggravate pathological responses of allergic asthma in mice. / Dissertation

Protein folding in the endoplasmic reticulum (ER) is essential for proper cellular function. However, the sensitive environment in the ER can be perturbed by both pathological processes as well as by physiological processes such as a large biosynthetic load placed on the ER. ER stress is a specific type of intracellular stress caused by the accumulation of immature or abnormal misfolded or unfolded proteins in the ER. Simply defined, ER stress is a disequilibrium between ER load and folding capacity. Cells have an adaptive response that counteracts ER stress called the "Unfolded Protein Response” (UPR). The ability to adapt to physiological levels of ER stress is especially important for maintaining ER homeostasis in secretory cells. This also holds true for pancreatic β-cells, which must fold and process large amounts of the hormone insulin. Pancreatic β-cells minimize abnormal levels of glycemia through adaptive changes in the production and regulated secretion of insulin. This process is highly sensitive, so that small degrees of hypo- or hyperglycemia result in altered insulin release. The frequent fluctuation of blood glucose levels in humans requires that β-cells control proinsulin folding in the ER with exquisite sensitivity. Any imbalance between the load of insulin translation into the ER and the actual capacity of the ER to properly fold and process the insulin negatively affects the homeostasis of β-cells and causes ER stress. In this dissertation, we show that Inositol Requiring 1 (IRE1), an ER-resident kinase/endoribonuclease and a central regulator of ER stress signaling, is essential for maintaining ER homeostasis in pancreatic β-cells. Importantly, IRE1 has a crucial function in the body’s normal production of insulin in response to high glucose. Phosphorylation and subsequent activation of IRE1 by transient exposure to high glucose is coupled to insulin biosynthesis, while inactivation of IRE1 by siRNA or inhibition of IRE1 phosphorylation abolishes insulin biosynthesis. IRE1 signaling under these physiological ER stress conditions utilizes a unique subset of downstream components of IRE1 and has a beneficial effect on pancreatic β-cell homeostasis. In contrast, we show that chronic exposure of β-cells to high glucose causes pathological levels of ER stress and hyperactivation of IRE1, leading to the degradation of insulin mRNA. The term “glucose toxicity” refers to impaired insulin secretion by β-cells in response to chronic stimulation by glucose and is characterized by a sharp decline in insulin gene expression. However, the molecular mechanisms of glucose toxicity are not well understood. We show that hyperactivation of IRE1 caused by chronic high glucose treatment or IRE1 overexpression leads to insulin mRNA degradation in pancreatic β-cells. Inhibition of IRE1 signaling using a dominant negative form of the protein prevents insulin mRNA degradation in β-cells. Additionally, islets from mice heterozygous for IRE1 retain expression of more insulin mRNA after chronic high glucose treatment than do their wild-type littermates. This work suggests that the rapid degradation of insulin mRNA could provide immediate relief for the ER and free up the translocation machinery. Thus, this mechanism may represent an essential element in the adaptation of β-cells to chronic hyperglycemia. This adaptation is crucial for the maintenance of β-cell homeostasis and may explain in part why the β-cells of diabetic patients with chronic hyperglycemia stop producing insulin without simply undergoing apoptosis. This work implies that prolonged activation of IRE1 signaling is involved in the molecular mechanisms underlying glucose toxicity. This work therefore reveals two distinct activities elicited by IRE1 in pancreatic β-cells. IRE1 signaling activated by transient exposure to high glucose enhances proinsulin biosynthesis, while chronic exposure of β-cells to high glucose causes hyperactivation of IRE1, leading to the degradation of insulin mRNA. Physiological IRE1 activation by transient high glucose levels in pancreatic β cells has a beneficial effect on insulin biosynthesis. However, pathological IRE1 activation by chronic high glucose or experimental drugs negatively affects insulin gene expression. In the future, a system to induce a physiological level of IRE1 activation, and/or reduce the pathological level of IRE1 activation could be used to enhance insulin biosynthesis and secretion in people with diabetes, and may lead to the development of new and more effective clinical approaches to the treatment of this disorder.