CIN85 Modulates the Down-regulation of FcγRIIa Expression and Function by c-Cbl in a PKC-dependent Manner in Human Neutrophils
Louis MaroisMyriam VaillancourtGuillaume ParéValérie GagnéMaria J. FernandesEmmanuelle Rollet‐LabellePaul H. Naccache
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We previously described a non-classical mechanism that arrests FcγRIIa signaling in human neutrophils once engaged by immune complexes or opsonized pathogens. The engagement of FcγRIIa leads to its ubiquitination by the ubiquitin ligase c-Cbl and degradation by the proteasome. Herein, we further examined some of the events regulating this novel pathway. The adaptor protein CIN85 was described in other systems to be involved in the regulation of the c-Cbl-dependent pathway. We found that CIN85 is expressed in human neutrophils and that it translocates like c-Cbl from the cytosol to the plasma membrane following receptor cross-linking. CIN85 was also recruited to the same subset of high density detergent-resistant membrane fractions in which stimulated FcγRIIa partitioned with c-Cbl. The integrity of these microdomains is essential to the FcγRIIa degradation process because the cholesterol-depleting agent methyl-β-cyclodextrin inhibits this event. Silencing the expression of CIN85 by siRNA in dibutyryl cyclic AMP-differentiated PLB 985 cells prevented FcγRIIa degradation and increased IgG-mediated phagocytosis. Confocal microscopy revealed that the presence of CIN85 is essential to the proper sorting of FcγRIIa during endocytosis. We also provide direct evidence that CIN85 is a substrate of serine/threonine kinase PKCs. Classical PKCs positively regulate FcγRIIa ubiquitination and degradation because these events were inhibited by Gö6976, a classical PKC inhibitor. We conclude that the ubiquitination and degradation of stimulated FcγRIIa mediated by c-Cbl are positively regulated by the adaptor protein CIN85 in a PKC-dependent manner and that these events contribute to the termination of FcγRIIa signaling.Keywords:
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The internalization of proteins plays a key role in cell development, cell signaling and immunity. We have previously developed a specific hybridization internalization probe (SHIP) to quantitate the internalization of proteins and particles into cells. Herein, we extend the utility of SHIP to examine both the endocytosis and recycling of surface receptors using flow cytometry. SHIP was used to monitor endocytosis of membrane-bound transferrin receptor (TFR) and its soluble ligand transferrin (TF). SHIP enabled measurements of the proportion of surface molecules internalized, the internalization kinetics and the proportion and rate of internalized molecules that recycle to the cell surface with time. Using this method, we have demonstrated the internalization and recycling of holo-TF and an antibody against the TFR behave differently. This assay therefore highlights the implications of receptor internalization and recycling, where the internalization of the receptor-antibody complex behaves differently to the receptor-ligand complex. In addition, we observe distinct internalization patterns for these molecules expressed by different subpopulations of primary cells. SHIP provides a convenient and high throughput technique for analysis of trafficking parameters for both cell surface receptors and their ligands.
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MiPEPs are short natural peptides encoded by microRNAs in plants. Exogenous application of miPEPs increases the expression of their corresponding miRNA and, consequently, induces consistent phenotypical changes. Therefore, miPEPs carry huge potential in agronomy as gene regulators that do not require genome manipulation. However, to this end, it is necessary to know their mode of action, including where they act and how they enter the plants. Here, after analyzing the effect of Arabidopsis thaliana miPEP165a on root and aerial part development, we followed the internalization of fluorescent-labelled miPEP165a into roots and compared its uptake into endocytosis-altered mutants to that observed in wild-type plants treated or not with endocytosis inhibitors. The results show that entry of miPEP165a involves both a passive diffusion at the root apex and endocytosis-associated internalization in the differentiation and mature zones. Moreover, miPEP165a is unable to enter the central cylinder and does not migrate from the roots to the aerial part of the plant, suggesting that miPEPs have no systemic effect.
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Abstract Nanoparticle-cell interactions begin with the cellular uptake of the nanoparticles, a process that eventually determines their cellular fate. In the present work, we show that the morphological features of nanodiamonds (NDs) affect both the anchoring and internalization stages of their endocytosis. While a prickly ND (with sharp edges/corners) has no trouble of anchoring onto the plasma membrane, it suffers from difficult internalization afterwards. In comparison, the internalization of a round ND (obtained by selective etching of the prickly ND) is not limited by its lower anchoring amount and presents a much higher endocytosis amount. Molecular dynamics simulation and continuum modelling results suggest that the observed difference in the anchoring of round and prickly NDs likely results from the reduced contact surface area with the cell membrane of the former, while the energy penalty associated with membrane curvature generation, which is lower for a round ND, may explain its higher probability of the subsequent internalization.
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This project was designed to determine whether neomycin, an aminoglycoside antibiotic, has a significant effect upon the pathways of ligand endocytosis in isolated rat hepatocytes. The pathways studied include receptor-mediated endocytosis and fluid-phase endocytosis. Neomycin causes a dose-dependent acceleration of {sup 125}I-insulin internalization. Since fluid-phase endocytosis can also be a significant factor in {sup 125}I-insulin internalization, lucifer yellow (LY), a marker for fluid-phase endocytosis, was incorporated into an assay similar to the {sup 125}I-insulin internalization procedure. In the presence of 5 mM neomycin, a significant increase in LY uptake was evident at 0.2 and 0.4 mg/ml of LY. At 0.8 mg/ml, a decrease in LY uptake was observed. The increased rate of {sup 125}I-insulin internalization in the presence of neomycin was intriguing. Since one action of neomycin is to inhibit phosphoinositidase C, it suggests that the phosphotidylinositol cycle may be involved in ligand internalization by hepatocytes. At low insulin concentrations, receptor-mediated uptake predominates. Fluid-phase uptake can become an important uptake route as insulin concentrations are increased. Since neomycin stimulates fluid-phase endocytosis, it must also be taken into account when measuring ligand internalization.
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The following endocytosis assay has been optimized to assess EGF-stimulated EGFR endocytosis; but could be modified to assess other ligand-stimulated endocytosis of plasma membrane receptors (for which fluorochrome-conjugated ligands are available to track their receptor internalization). In brief, cells are treated with fluorescent EGF at 4 °C to allow binding to the receptor, but not internalization; then, endocytosis is allowed at 37 °C for different timepoints. For the setting up of this protocol we are really indebted to Dr. Letizia Lanzetti (Lanzetti et al., 2000).
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Abstract In a companion report (Moss and Ward: J. Cell. Physiol. 149:313–318, 1991) evidence was presented for multiple pathways for insulin internalization based on differences between the internalization of insulin and that of two other ligands, asialofetuin (Afet) and epidermal growth factor (EGF), in the presence of several perturbations of endocytosis. In the present study we have explored the characteristics of three internalization pathways and the contribution of each to overall insulin uptake. Freshly isolated hepatocytes were incubated with radiolabeled ligands in the presence of hyperosmolar sucrose, treatment that is thought to inhibit the coated pit pathway of endocytosis. Insulin internalization was decreased approximately 39%, but much greater decreases were observed with Afet (86%) and EGF (62%). Competition between uptake of radiolabeled and unlabeled insulin was observed in hyperosmolar‐treated cells, suggestive of endocytosis by a receptor‐mediated noncoated‐pit pathway. Uptake of radiolabeled insulin that persisted in the presence of hyperosmolarity and high concentrations of unlabeled insulin suggested a third uptake pathway: fluid‐phase endocytosis. A rate of fluid‐phase endocytosis of 7.2 μL/hr/10 6 cells was determined from the uptake of the fluid‐phase marker lucifer yellow. At high insulin concentrations (≥ 250 ng/ml), fluid‐phase endocytosis appears to be the predominant pathway for insulin uptake, but at lower insulin concentrations (physiological) the coated pit and noncoated pit pathways are the primary routes for insulin internalization.
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Abstract We reported here an alternative strategy of antibody internalization by crosslinker-mediated endocytosis. This crosslinker consists of IgG binding peptide and folic acid as cancer targeting ligands toward the folate receptor, which highly expresses in many cancer cells surface. This crosslinker successfully facilitated antibody internalization into cancer cell by the folate receptor-mediated endocytosis.
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