Biomedical subjects

Frédéric Delom

Publications and source records attributed to Frédéric Delom.

7 recordsLinked to original sources

PubMed2007

Regulation of calnexin sub-cellular localization modulates endoplasmic reticulum stress-induced apoptosis in MCF-7 cells.

The endoplasmic reticulum (ER) is the cellular compartment where proteins enter the secretory pathway, undergo post-translational modifications and acquire a correct conformation. If these functions are chronically altered, specific ER stress signals are triggered to promote cell death through the intrinsic apoptotic pathway. Here, we show that tunicamycin causes significant alteration of calnexin sub-cellular distribution in MCF-7 cells. Interestingly, this correlates with the absence of both tunicamycin-induced calnexin phosphorylation as well as tunicamycin-induced cell death. Under these conditions, calnexin-associated Bap31, an ER integral membrane protein, is subjected to a caspase-8 cleavage pattern within a specific sub-compartment of the ER. These results suggest that MCF-7 resistance to ER stress-induced apoptosis is partially mediated by the expression level of calnexin which in turn controls its sub-cellular localization, and its association with Bap31. These data may delineate a resistance mechanism to the ER stress-induced intrinsic apoptotic pathway.

Animals↗

PubMed2007

Separation, identification, and profiling of membrane proteins by GFC/IEC/SDS-PAGE and MALDI TOF MS.

Membrane protein identification by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) requires that proteins be separated prior to MS analysis. After membrane solubilization with the nondenaturing detergent n-dodecyl-beta-D-maltoside, proteins can be separated by ion-exchange chromatography (IEC) and further resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). An additional separation step by gel filtration (GF) before IEC/SDS-PAGE can be required depending on the complexity of the membrane protein mixture. Staining of final SDS-PAGE gels allows one to establish simply the protein expression pattern of a membrane fraction and to profile responses. Moreover, in-gel digestion of hydrophobic integral proteins is valuable. Finally, the resolution capacity of this separation procedure allows identification of proteins by MALDI-TOF MS. The method is illustrated by application to plant and yeast plasma membrane and to plant vacuolar membrane.

Cell Fractionation↗

PubMed2006

Tat-mediated protein delivery in living Caenorhabditis elegans.

The Tat protein from HIV-1 fused with heterologous proteins traverses biological membranes in a transcellular process called: protein transduction. This has already been successfully exploited in various biological models, but never in the nematode worm Caenorhabditis elegans. TAT-eGFP or GST-eGFP proteins were fed to C. elegans worms, which resulted in the specific localization of Tat-eGFP to epithelial intestinal cells. This system represents an efficient tool for transcellular transduction in C. elegans intestinal cells. Indeed, this approach avoids the use of tedious purification steps to purify the TAT fusion proteins and allows for rapid analyses of the transduced proteins. In addition, it may represent an efficient tool to functionally analyze the mechanisms of protein transduction as well as to complement RNAi/KO in the epithelial intestinal system. To sum up, the advantage of this technology is to combine the potential of bacterial expression system and the Tat-mediated transduction technique in living worm.

Animals↗

PubMed2006

Phosphoprotein analysis: from proteins to proteomes.

Characterization of protein modification by phosphorylation is one of the major tasks that have to be accomplished in the post-genomic era. Phosphorylation is a key reversible modification occurring mainly on serine, threonine and tyrosine residues that can regulate enzymatic activity, subcellular localization, complex formation and degradation of proteins. The understanding of the regulatory role played by phosphorylation begins with the discovery and identification of phosphoproteins and then by determining how, where and when these phosphorylation events take place. Because phosphorylation is a dynamic process difficult to quantify, we must at first acquire an inventory of phosphoproteins and characterize their phosphorylation sites. Several experimental strategies can be used to explore the phosphorylation status of proteins from individual moieties to phosphoproteomes. In this review, we will examine and catalogue how proteomics techniques can be used to answer specific questions related to protein phosphorylation. Hence, we will discuss the different methods for enrichment of phospho-proteins and -peptides, and then the various technologies for their identification, quantitation and validation.

Journal Article↗

PubMed2006

Proteomic analysis of ischemia-reperfusion injury upon human liver transplantation reveals the protective role of IQGAP1.

Ischemia-reperfusion injury (IRI) represents a major determinant of liver transplantation. IRI-induced graft dysfunction is related to biliary damage, partly due to a loss of bile canaliculi (BC) integrity associated with a dramatic remodeling of actin cytoskeleton. However, the molecular mechanisms associated with these events remain poorly characterized. Using liver biopsies collected during the early phases of organ procurement (ischemia) and transplantation (reperfusion), we characterized the global patterns of expression and phosphorylation of cytoskeleton-related proteins during hepatic IRI. This targeted functional proteomic approach, which combined protein expression pattern profiling and phosphoprotein enrichment followed by mass spectrometry analysis, allowed us to identify IQGAP1, a Cdc42/Rac1 effector, as a potential regulator of actin cytoskeleton remodeling and maintenance of BC integrity. Cell fractionation and immunohistochemistry revealed that IQGAP1 expression and localization were affected upon IRI and related to actin reorganization. Furthermore using an IRI model in human hepatoma cells, we demonstrated that IQGAP1 silencing decreased the basal level of actin polymerization at BC periphery, reflecting a defect in BC structure coincident with reduced cellular resistance to IRI. In summary, this study uncovered new mechanistic insights into the global regulation of IRI-induced cytoskeleton remodeling and led to the identification of IQGAP1 as a regulator of BC structure. IQGAP1 therefore represents a potential target for the design of new organ preservation strategies to improve transplantation outcome.

Actins↗

PubMed2006

In vitro mapping of calnexin interaction with ribosomes.

Calnexin is an endoplasmic reticulum (ER) resident type I integral membrane phosphoprotein. This protein is actively involved in the ER glycoprotein quality control through its luminal domain. In addition, although calnexin also interacts with membrane-bound ribosomes, the nature of this interaction remains poorly characterized. Herein, using in vitro approaches, we demonstrate that calnexin cytosolic domain directly interacts with, at least 5 ribosomal proteins. Furthermore, we characterize more specifically its interaction with the ribosomal protein L4 and that L4 binds to the 19 carboxy terminal amino acids of calnexin. We suggest that the direct interaction of calnexin with membrane-bound ribosomes may represent a regulatory mechanism for its lectin-like chaperone function.

Binding Sites↗

PubMed2006

The plasma membrane proteome of Saccharomyces cerevisiae and its response to the antifungal calcofluor.

Calcofluor is an antifungal compound known to induce structural perturbations of the cell wall by interfering with the synthesis of chitin microfibril. Proteins from a stripped plasma membrane fraction were solubilized with the neutral and non-denaturing detergent, the n-dodecyl beta-D-maltoside. Proteins were then resolved using a recently described ion-exchange chromatography (IEC)/lithium dodecyl sulfate (LDS)-PAGE procedure. Nearly 90 proteins were identified and clustered, based on their pI, molecular weight, abundance and/or hydrophobicity. This method was then applied to profile the plasma membrane response to calcofluor. The LDS-PAGE patterns obtained from whole plasma membrane proteins were similar for the non-treated and calcofluor-treated samples. However, IEC/LDS-PAGE analysis revealed subtle changes in the expression of several proteins of low abundance, in response to calcofluor. These proteins include Pil1p and Lsp1p, two sphingolipid long-chain base-responsive inhibitors of protein kinases involved in signaling pathways for cell wall integrity and Rho1p, a small GTPase. It was recently hypothesized that Pil1p and Lsp1p could associate with, and regulate, the plasma membrane beta-1-3-glucan synthase, responsible for the synthesis of another major microfibril for yeast cell wall. Results are discussed with respect to both calcofluor effects on the plasma membrane proteins and the power of the IEC/LDS-PAGE procedure in the search for new potential therapeutics targets.

Antifungal Agents↗