Regulation Of Endoplasmic Reticulum Function Research Articles

Nucleotide exchange factor SIL1 promotes the progress of breast cancer cells via regulating the cell cycle and apoptosis.

Breast cancer, as one of the most malignant tumors, poses a serious threat to the lives of females. Nucleotide exchange factor SIL1 is an important regulator of endoplasmic reticulum function that might have a specific role in tumor progression. In this study, we aimed to investigate the effect of SIL1 on the proliferation, apoptosis, and metastasis of human breast cancer. SIL1-specific small interfering RNA was transfected into two breast cancer cell lines, MCF7 and MDA-MB-231, to generate SIL1 knockdown cells. Clone formation and Cell Counting Kit-8 assays were performed to determine cell proliferation. Wound healing and transwell assays were used to detect the cell migration and invasion, respectively. Cell cycle and apoptosis were determined by flow cytometry. The messenger RNA and protein levels of target genes were analyzed using quantitative real-time PCR and western blot. According to the results of TCGA and GTEx database analysis, we determined that SIL1 was overexpressed in 1085 breast cancer samples compared with 291 normal samples. Knockdown of SIL1 inhibited the proliferation, migration, and invasion of MCF7 and MDA-MB-231 cells, accordingly. The cell cycle was blocked at the G1 phase following transfection of SIL1-specific small interfering RNA through the inhibition of Cyclin D1, CDK4, and CDK6. SIL1 knockdown induced apoptosis and also promoted the activity of Caspase9 and Bax. Furthermore, SIL1 was able to promote phosphorylation of ERK1/2. Based on these results, SIL1 might act as an oncogene and accelerate the progression of human breast cancer.

Ufm1-Specific Ligase Ufl1 Regulates Endoplasmic Reticulum Homeostasis and Protects Against Heart Failure.

Defects in protein homeostasis are sufficient to provoke cardiac remodeling and dysfunction. Although posttranslational modifications by ubiquitin and ubiquitin-like proteins are emerging as an important regulatory mechanism of protein function, the role of Ufm1 (ubiquitin-fold modifier 1)-a novel ubiquitin-like protein-has not been explored in either the normal or stressed heart. Western blotting revealed that Ufl1 (Ufm1-specific E3 ligase 1)-an enzyme essential for Ufm1 modification-was increased in hypertrophic mouse hearts but reduced in the failing hearts of patients with dilated cardiomyopathy. To determine the functional role of Ufl1 in the heart, we generated a cardiac-specific knockout mouse and showed that Ufl1-deficient mice developed age-dependent cardiomyopathy and heart failure, as indicated by elevated cardiac fetal gene expression, increased fibrosis, and impaired cardiac contractility. When challenged with pressure overload, Ufl1-deficient hearts exhibited remarkably greater hypertrophy, exacerbated fibrosis, and worsened cardiac contractility compared with control counterparts. Transcriptome analysis identified that genes associated with the endoplasmic reticulum (ER) function were dysregulated in Ufl1-deficient hearts. Biochemical analysis revealed that excessive ER stress preceded and deteriorated along with the development of cardiomyopathy in Ufl1-deficient hearts. Mechanistically, Ufl1 depletion impaired (PKR-like ER-resident kinase) signaling and aggravated cardiomyocyte cell death after ER stress. Administration of the chemical ER chaperone tauroursodeoxycholic acid to Ufl1-deficient mice alleviated ER stress and attenuated pressure overload-induced cardiac dysfunction. Our results advance a novel concept that the Ufm1 system is essential for cardiac homeostasis through regulation of ER function and that upregulation of myocardial Ufl1 could be protective against heart failure.

Abstract 530: The Ufm1 Specific Ligase 1 Regulates Endoplasmic Reticulum Homeostasis and Protects Against Heart Failure

Protein modifications by ubiquitin and ubiquitin-like proteins are emerging as an important regulatory mechanism of protein function and involved in various cellular processes. Ufm1 (ubiquitin-fold modifier 1) is a novel ubiquitin-like protein that modifies protein targets in a UBA5 (E1) - Ufc1 (E2) - Ufl1 (E3) dependent manner. While defects in ubiquitin- and SUMO-modification have been shown to provoke cardiac remodeling and dysfunction, the importance of Ufm1 modification has not been explored in the normal and stressed heart. Western blotting revealed that Ufm1 specific ligase 1 (Ufl1), an enzyme essential for Ufm1 modification, was increased in hypertrophic mouse hearts but reduced in the failing hearts of patients with dilated cardiomyopathy. To determine the functional role of Ufl1 in the heart, we generated a cardiac-specific knockout mouse and showed that Ufl1-deficient mice developed age-dependent cardiomyopathy and heart failure, as indicated by elevated cardiac fetal gene expression, increased fibrosis and impaired cardiac contractility. When challenged with pressure overload, Ufl1-deficient hearts exhibited remarkably greater hypertrophy, exacerbated fibrosis and worsened cardiac contractility compared with control counterparts. Transcriptome analysis identified that genes associated with the endoplasmic reticulum (ER) function were dysregulated in Ufl1-deficient hearts. Biochemical analysis revealed that excessive ER stress preceded and deteriorated along with the development of cardiomyopathy in Ufl1-deficient hearts. Mechanistically, Ufl1 depletion impaired PERK signaling and aggravated cardiomyocyte cell death following ER stress. Administration of the chemical ER chaperone tauroursodeoxycholic acid to Ufl1-deficient mice alleviated ER stress and attenuated pressure overload-induced cardiac dysfunction. Our results advance a novel concept that the Ufm1 system is essential for cardiac homeostasis through regulation of ER function and that upregulation of myocardial Ufl1 could be protective against heart failure.

Zinc Transporter SLC39A7/ZIP7 Promotes Intestinal Epithelial Self-Renewal by Resolving ER Stress.

Zinc transporters play a critical role in spatiotemporal regulation of zinc homeostasis. Although disruption of zinc homeostasis has been implicated in disorders such as intestinal inflammation and aberrant epithelial morphology, it is largely unknown which zinc transporters are responsible for the intestinal epithelial homeostasis. Here, we show that Zrt-Irt-like protein (ZIP) transporter ZIP7, which is highly expressed in the intestinal crypt, is essential for intestinal epithelial proliferation. Mice lacking Zip7 in intestinal epithelium triggered endoplasmic reticulum (ER) stress in proliferative progenitor cells, leading to significant cell death of progenitor cells. Zip7 deficiency led to the loss of Olfm4+ intestinal stem cells and the degeneration of post-mitotic Paneth cells, indicating a fundamental requirement for Zip7 in homeostatic intestinal regeneration. Taken together, these findings provide evidence for the importance of ZIP7 in maintenance of intestinal epithelial homeostasis through the regulation of ER function in proliferative progenitor cells and maintenance of intestinal stem cells. Therapeutic targeting of ZIP7 could lead to effective treatment of gastrointestinal disorders.

AB5 subtilase cytotoxin inactivates the endoplasmic reticulum chaperone BiP

AB5 toxins are produced by pathogenic bacteria and consist of enzymatic A subunits that corrupt essential eukaryotic cell functions, and pentameric B subunits that mediate uptake into the target cell. AB5 toxins include the Shiga, cholera and pertussis toxins and a recently discovered fourth family, subtilase cytotoxin, which is produced by certain Shiga toxigenic strains of Escherichia coli. Here we show that the extreme cytotoxicity of this toxin for eukaryotic cells is due to a specific single-site cleavage of the essential endoplasmic reticulum chaperone BiP/GRP78. The A subunit is a subtilase-like serine protease; structural studies revealed an unusually deep active-site cleft, which accounts for its exquisite substrate specificity. A single amino-acid substitution in the BiP target site prevented cleavage, and co-expression of this resistant protein protected transfected cells against the toxin. BiP is a master regulator of endoplasmic reticulum function, and its cleavage by subtilase cytotoxin represents a previously unknown trigger for cell death.

Intraluminal calcium as a primary regulator of endoplasmic reticulum function

The concentration of Ca 2+ inside the lumen of endoplasmic reticulum (ER) regulates a vast array of spatiotemporally distinct cellular processes, from intracellular Ca 2+ signals to intra-ER protein processing and cell death. This review summarises recent data on the mechanisms of luminal Ca 2+-dependent regulation of Ca 2+ release and uptake as well as ER regulation of cellular adaptive processes. In addition we discuss general biophysical properties of the ER membrane, as trans-endomembrane Ca 2+ fluxes are subject to basic electrical forces, determined by factors such as the membrane potential of the ER and the ease with which Ca 2+ fluxes are able to change this potential (i.e. the resistance of the ER membrane). Although these electrical forces undoubtedly play a fundamental role in shaping [Ca 2+] ER dynamics, at present there is very little direct experimental information about the biophysical properties of the ER membrane. Further studies of how intraluminal [Ca 2+] is regulated, best carried out with direct measurements, are vital for understanding how Ca 2+ orchestrates cell function. Direct monitoring of [Ca 2+] ER under conditions where the cytosolic [Ca 2+] is known may also help to capture elusive biophysical information about the ER, such as the potential difference across the ER membrane.