Number Of Molecular Chaperones Research Articles

Elucidation of molecular mechanism of the unfolded protein response.

The endoplasmic reticulum (ER), where newly synthesized secretory and transmembrane proteins are folded and assembled, has the ability to discriminate folded proteins from unfolded proteins and controls the quality of synthesized proteins. Only correctly folded molecules are allowed to move along the secretory pathway, whereas unfolded proteins are retained in the ER.The ER contains a number of molecular chaperones and folding enzymes (ER chaperones hereafter), which assist productive folding of proteins, and therefore newly synthesized proteins usually gain correct tertiary and quaternary structures quite efficiently. Yet unfolded or misfolded proteins even after assistance of ER chaperones are retrotranslocated back to the cytosol, ubiquitinated and degraded by the proteasome. This disposal system is called ER-associated degradation (ERAD). Thus, the quality of proteins in the ER is ensured by two distinct mechanisms, productive folding and ERAD, which have opposite directions.Under a variety of conditions collectively termed ER stress, however, unfolded or misfolded proteins accumulate in the ER, which in turn activates ER stress response or Unfolded Protein Response (UPR). The UPR is mediated by transmembrane proteins in the ER, and three ER stress sensors/transducers, namely IRE1, PERK and ATF6, operates ubiquitously in mammals. Thanks to these signaling pathways, translation is generally attenuated to decrease the burden on the folding machinery; transcription of ER chaperones is induced to augment folding capacity; and transcription of components of ERAD machinery is induced to enhance degradation capacity, leading to maintenance of the homeostasis of the ER. If ER stress sustains, cells undergo to apoptosis.I will talk on the mechanism, evolution, and physiological importance of the UPR and ERAD as well as its involvement in development and progression of various diseases.

Larp6 Regulates Collagen mRNA by Targeted Unwinding of a Conserved Stem‐Loop

Collagen is the most abundant protein in the human body and a key component of the extracellular matrix. Regulation of collagen production in key to the development of fibroproliferative disorders; everything from scarring to cardiovascular disease. La ribonucleoprotein 6 (Larp6) is an RNA binding protein which has recently been shown to regulate collagen production by binding to a conserved region at the translation start site of collagen mRNA. This interaction appears to be critical to directing RNA to the rough ER for translation initiation. Additionally, LARP6 interaction with a number of molecular chaperones appears to be important for regulating collagen production. We hypothesize that LARP6 utilizes conformational selection in the recognition and discrimination of collagen mRNAs and that tertiary interactions dictate mRNA fate. In vitro RNA chaperone assays, translation assays, RNAi, confocal microscopy, and NMR and SAX structural studies are employed to interrogate these interactions. New information regarding the structures and dynamics that determine the Larp6 interaction with collagen mRNA may inform novel therapeutic targets that can mitigate fibroproliferative disease.Support or Funding InformationP20GM109095

Comparative proteomic analysis revealed complex responses to classical/novel duck reovirus infections in Cairna moschata

Duck reovirus (DRV) is an typical aquatic bird pathogen belonging to the Orthoreovirus genus of the Reoviridae family. Reovirus causes huge economic losses to the duck industry. Although DRV has been identified and isolated long ago, the responses of Cairna moschata to classical/novel duck reovirus (CDRV/NDRV) infections are largely unknown. To investigate the relationship of pathogenesis and immune response, proteomes of C. moschata liver cells under the C/NDRV infections were analyzed, respectively. In total, 5571 proteins were identified, among which 5015 proteins were quantified. The differential expressed proteins (DEPs) between the control and infected liver cells displayed diverse biological functions and subcellular localizations. Among the DEPs, most of the metabolism-related proteins were down-regulated, suggesting a decrease in the basal metabolisms under C/NDRV infections. Several important factors in the complement, coagulation and fibrinolytic systems were significantly up-regulated by the C/NDRV infections, indicating that the serine protease-mediated innate immune system might play roles in the responses to the C/NDRV infections. Moreover, a number of molecular chaperones were identified, and no significantly changes in their abundances were observed in the liver cells. Our data may give a comprehensive resource for investigating the regulation mechanism involved in the responses of C. moschata to the C/NDRV infections.

A new strategy of promoting cisplatin chemotherapeutic efficiency by targeting endoplasmic reticulum stress

Cisplatin (cis-diamminedichloroplatinum II, CDDP) is one of the most effective chemotherapeutic agents and is widely used in the treatment of solid tumors. However, its side effects and acquired resistance gained during the course of treatment may limit its usage. It is generally considered to be a cytotoxic drug that kills cancer cells by damaging their DNA and inhibiting DNA synthesis to induce apoptosis via the mitochondrial death pathway or through plasma membrane disruption, triggering the Fas death receptor pathway. The endoplasmic reticulum (ER) is one of the most important protein-folding compartments within the cell and an intracellular Ca2+ storage organelle. The ER contains a number of molecular chaperones, which may play an important role in determining cellular sensitivity to ER stress and apoptosis. The aim of this review was to summarize our current understanding regarding the mechanisms of ER stress response by which cisplatin induces cell death and the basis for cisplatin resistance. Various aspects were addressed, including the two-way regulation of ER stress, the involvement of ER stress in cisplatin-induced cell death and drug resistance and the drugs enhancing cisplatin-induced cell death by interfering with ER stress. An understanding of how ER stress signaling pathways regulate cisplatin-induced cell death may enable the development of more effective therapeutic strategies for the treatment of cancer.

The yeast prion protein Ure2: insights into the mechanism of amyloid formation

Ure2, a regulator of nitrogen metabolism, is the protein determinant of the [URE3] prion state in Saccharomyces cerevisiae. Upon conversion into the prion form, Ure2 undergoes a heritable conformational change to an amyloid-like aggregated state and loses its regulatory function. A number of molecular chaperones have been found to affect the prion properties of Ure2. The studies carried out in our laboratory have been aimed at elucidating the structure of Ure2 fibrils, the mechanism of amyloid formation and the effect of chaperones on the fibril formation of Ure2.

The Aryl Hydrocarbon Receptor-interacting Protein (AIP) Is Required for Dioxin-induced Hepatotoxicity but Not for the Induction of the Cyp1a1 and Cyp1a2 Genes

The aryl hydrocarbon receptor (AHR) plays an essential role in the toxic response to environmental pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin), in the adaptive up-regulation of xenobiotic metabolizing enzymes, and in hepatic vascular development. In our model of AHR signaling, the receptor is found in a cytosolic complex with a number of molecular chaperones, including Hsp90, p23, and the aryl hydrocarbon receptor-interacting protein (AIP), also known as ARA9 and XAP2. To understand the role of AIP in adaptive and toxic aspects of AHR signaling, we generated a conditional mouse model where the Aip locus can be deleted in hepatocytes. Using this model, we demonstrate two important roles for the AIP protein in AHR biology. (i) The expression of AIP in hepatocytes is essential to maintain high levels of functional cytosolic AHR protein in the mammalian liver. (ii) Expression of the AIP protein is essential for dioxin-induced hepatotoxicity. Interestingly, classical AHR-driven genes show differential dependence on AIP expression. The Cyp1b1 and Ahrr genes require AIP expression for normal up-regulation by dioxin, whereas Cyp1a1 and Cyp1a2 do not. This differential dependence on AIP provides evidence that the mammalian genome contains more than one class of AHR-responsive genes and suggests that a search for AIP-dependent, AHR-responsive genes may guide us to the targets of the dioxin-induced hepatotoxicity.

Identification of the Molecular Chaperone, Heat Shock Protein 1 (Chaperonin 10), in the Reproductive Tract and in Capacitating Spermatozoa in the Male Mouse1

Mammalian spermatozoa must undergo epididymal maturation in the male reproductive tract and capacitation in the female tract before acquiring the ability to fertilize an oocyte. Previous studies from our laboratory have demonstrated a causal relationship between capacitation-associated surface phosphotyrosine expression and the ability of mouse spermatozoa to recognize the oocyte and engage in sperm-zona pellucida interaction. Our previous analyses of the surface phosphoproteome of capacitated murine spermatozoa identified two molecular chaperones, heat shock protein (HSP) D1 and HSP90B1, with well-characterized roles in protein folding and the assemblage of multimeric protein complexes. The expression of these chaperones was restricted to the rostral aspect of the sperm head, in an ideal position to mediate sperm-zona pellucida interaction. Herein, we report the characterization of an additional chaperone in this location, HSPE1 (chaperonin 10; HSP10). This chaperone was identified using a coimmunoprecipitation strategy employing HSPD1 as bait. The putative interaction between HSPE1 and HSPD1 was supported by reciprocal immunoprecipitation and colocalization studies, which demonstrated the coordinated appearance of both proteins on the surface of the sperm head during capacitation. However, the surface exposure of the protein was lost upon induction of acrosomal exocytosis, as would be expected of a protein potentially involved in sperm-zona pellucida interaction. Collectively, these data invite speculation that a number of molecular chaperones are involved in modification of the sperm surface during capacitation to render these cells functionally competent to engage the process of fertilization.

Stress wars: the direct role of host and bacterial molecular chaperones in bacterial infection.

Stress wars: the direct role of host and bacterial molecular chaperones in bacterial infection.

Evidence for Importin αIndependent Nuclear Translocation of Glucocorticoid Receptors in Xenopus laevis Oocytes

The glucocorticoid receptor (GR) is a ligand-dependent transcription factor which resides in the cytoplasm as a complex with a number of molecular chaperones. Upon hormonal stimulation, the GR is translocated into the nucleus where it modulates transcription by binding to specific target DNA sequences. GR contains a classical basic nuclear localization signal (NLS) and a second, only poorly characterized NLS. Though the participation of the importin α/importin β pathway in nuclear import of GR has been postulated, relatively little is known about its dynamics and mechanisms. We analyzed the hormone-driven nuclear import of rat GR expressed in Xenopus laevis oocytes by atomic force microscopy (AFM) and western blot analysis. AFM imaging revealed accumulation of macromolecules matching the size of GR at the nuclear envelope beginning 5 min after glucocorticoid hormone injection. In parallel, western blot analysis showed accumulation of GR over the same time scale after glucocorticoid hormone stimulation. Nuclear GR import did not trigger redistribution of importin α or importin β. We conclude that hormone-driven nuclear import of rat GR expressed in Xenopus oocytes is a process with limited capacity and involves mechanisms different from the importin α/importin β pathway. This represents a restriction of nuclear import downstream of import signals.

The peptide-loading complex and ligand selection during the assembly of HLA class I molecules

The identification and characterisation of the class I peptide loading complex has resulted in an appreciation of the co-ordinated and multifaceted nature of HLA class I assembly in the lumen of the endoplasmic reticulum. This loading complex consists of the assembling class I heterodimer in association with a number of molecular chaperones. These chaperones can be classified as generic to the folding of most glycoproteins in the endoplasmic reticulum or specific to the class I loading pathway. The functions of the various components of the loading complex in class I molecule assembly are reviewed. A critical component of the class I loading complex is the specialised chaperone tapasin. The role of tapasin in the stabilisation and retention of empty or suboptimally loaded class I molecules and the facilitation of the loading of these molecules with more appropriate ligands is discussed. As such, it is proposed that tapasin is a major determinant of peptide repertoire selection for class I-restricted presentation in normal antigen presenting cells. The potential implications in vaccine design and autoimmunity are discussed.

Protein biogenesis: Chaperones for nascent polypeptides

A number of molecular chaperones have been found to interact with nascent polypeptides attached to ribosomes, allowing these protein-synthesis machines to play a key part in protein folding and targeting.