RESUMO
The disruption of the energy or nutrient balance triggers endoplasmic reticulum (ER) stress, a process that mobilizes various strategies, collectively called the unfolded protein response (UPR), which reestablish homeostasis of the ER and cell. Activation of the UPR stress sensor IRE1α (inositol-requiring enzyme 1α) stimulates its endoribonuclease activity, leading to the generation of the mRNA encoding the transcription factor XBP1 (X-box binding protein 1), which regulates the transcription of genes encoding factors involved in controlling the quality and folding of proteins. We found that the activity of IRE1α was regulated by the ER oxidoreductase PDIA6 (protein disulfide isomerase A6) and the microRNA miR-322 in response to disruption of ER Ca2+ homeostasis. PDIA6 interacted with IRE1α and enhanced IRE1α activity as monitored by phosphorylation of IRE1α and XBP1 mRNA splicing, but PDIA6 did not substantially affect the activity of other pathways that mediate responses to ER stress. ER Ca2+ depletion and activation of store-operated Ca2+ entry reduced the abundance of the microRNA miR-322, which increased PDIA6 mRNA stability and, consequently, IRE1α activity during the ER stress response. In vivo experiments with mice and worms showed that the induction of ER stress correlated with decreased miR-322 abundance, increased PDIA6 mRNA abundance, or both. Together, these findings demonstrated that ER Ca2+, PDIA6, IRE1α, and miR-322 function in a dynamic feedback loop modulating the UPR under conditions of disrupted ER Ca2+ homeostasis.
Assuntos
Cálcio/metabolismo , Estresse do Retículo Endoplasmático/fisiologia , Retículo Endoplasmático/metabolismo , Homeostase/fisiologia , MicroRNAs/metabolismo , Isomerases de Dissulfetos de Proteínas/metabolismo , Animais , Células COS , Chlorocebus aethiops , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Retículo Endoplasmático/genética , Endorribonucleases/genética , Endorribonucleases/metabolismo , Camundongos , Camundongos Knockout , MicroRNAs/genética , Células NIH 3T3 , Isomerases de Dissulfetos de Proteínas/genética , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , Fatores de Transcrição de Fator Regulador X , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteína 1 de Ligação a X-BoxRESUMO
Acinetobacter baumannii is a common multidrug-resistant clinical pathogen that is often found in hospitals. The A. baumannii phosphoglycerate kinase (AbPGK) is involved in the key energy-producing pathway of glycolysis and presents a potential target for antibiotic development. AbPGK has been expressed and purified; it was crystallized using lithium sulfate as the precipitant. The AbPGK crystals belonged to space group P222(1). They diffracted to a resolution of 2.5â Å using synchrotron radiation at the Canadian Light Source.