Maturation and persistence of the anti-SARS-CoV-2 memory B cell response

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Intracellular localization of lipoprotein lipase in adipose cells

Subcellular localization of lipoprotein lipase has been examined in differentiated Ob17 adipose cells. No patent activity is detectable in carefully homogenized cells. All latent activity can be unmasked by disrupting membrane structures with neutral detergents. The sequestration of lipoprotein lipase in closed membrane structures is supported by experiments of immunotitration with anti-lipoprotein lipase antibodies and by experiments showing a full protection of the masked activity against proteolytic attack by trypsin. The intracellular distribution of lipoprotein lipase investigated by immunofluorescence staining and by isopycnic centrifugation indicates that a large proportion of the enzyme is located in the Golgi apparatus, in which the activation of the enzyme is likely to take place (C. Vannier et al. (1985) J. Biol. Chem. 260, 4424-4431). Altogether, the results are in favor of a localization of lipoprotein lipase in adipose cells as being typical of that of a secretory protein and underline the absence of lipoprotein lipase in the cell cytoplasm.     

Functional and molecular characterization of the conserved Arabidopsis PUMILIO protein,APUM9

Plant Molecular Biology - Here we demonstrate that the APUM9 RNA-binding protein and its co-factors play a role in mRNA destabilization and how this activity might regulate early plant development....     

Computational Modelling of Metastasis Development in Renal Cell Carcinoma

The biology of the metastatic colonization process remains a poorly understood phenomenon. To improve our knowledge of its dynamics, we conducted a modelling study based on multi-modal data from an orthotopic murine experimental system of metastatic renal cell carcinoma. The standard theory of metastatic colonization usually assumes that secondary tumours, once established at a distant site, grow independently from each other and from the primary tumour. Using a mathematical model that translates this assumption into equations, we challenged this theory against our data that included: 1) dynamics of primary tumour cells in the kidney and metastatic cells in the lungs, retrieved by green fluorescent protein tracking, and 2) magnetic resonance images (MRI) informing on the number and size of macroscopic lesions. Critically, when calibrated on the growth of the primary tumour and total metastatic burden, the predicted theoretical size distributions were not in agreement with the MRI observations. Moreover, tumour expansion only based on proliferation was not able to explain the volume increase of the metastatic lesions. These findings strongly suggested rejection of the standard theory, demonstrating that the time development of the size distribution of metastases could not be explained by independent growth of metastatic foci. This led us to investigate the effect of spatial interactions between merging metastatic tumours on the dynamics of the global metastatic burden. We derived a mathematical model of spatial tumour growth, confronted it with experimental data of single metastatic tumour growth, and used it to provide insights on the dynamics of multiple tumours growing in close vicinity. Together, our results have implications for theories of the metastatic process and suggest that global dynamics of metastasis development is dependent on spatial interactions between metastatic lesions.     

Maturation and secretion of lipoprotein lipase in cultured adipose cells. I. Intracellular activation of the enzyme

The intracellular pathway and the activation of lipoprotein lipase have been examined in differentiated Ob17 cells. These adipose cells were previously shown to secrete lipoprotein lipase during exposure to heparin. Treatment of the cells with cycloheximide and heparin leads to enzyme depletion, as shown by activity measurement and immunofluorescence microscopy. The repletion phase has been studied in the presence of monensin or carbonyl cyanide m-chlorophenylhydrazone, ionophores known to affect the intracellular transport of membrane and secretory proteins. Monensin-treated cells synthesize fully active lipoprotein lipase. Under these conditions the antigen accumulates in the Golgi apparatus and the heparin-stimulated enzyme release is extensively reduced. Carbonyl cyanide m-chlorophenylhydrazone-treated cells do not contain any enzyme activity but show detectable antigen which accumulates in the endoplasmic reticulum. Competition for binding to immobilized anti-lipoprotein lipase antibodies of mature and endoplasmic reticulum-sequestered antigens is observed. Carbonyl cyanide m-chlorophenylhydrazone removal is rapidly followed by a transient burst of enzyme activity and a redistribution of the antigen in the different subcellular compartments. Therefore, the results show that the activation of lipoprotein lipase is an intracellular event taking place after the enzyme exits from the endoplasmic reticulum and before it reaches the trans-Golgi cisternae.     

RNA-dependent dynamic histone acetylation regulates MCL1 alternative splicing

Histone deacetylases (HDACs) and lysine acetyltransferases (KATs) catalyze dynamic histone acetylation at regulatory and coding regions of transcribed genes. Highly phosphorylated HDAC2 is recruited within corepressor complexes to regulatory regions, while the nonphosphorylated form is associated with the gene body. In this study, we characterized the nonphosphorylated HDAC2 complexes recruited to the transcribed gene body and explored the function of HDAC-complex-mediated dynamic histone acetylation. HDAC1 and 2 were coimmunoprecipitated with several splicing factors, including serine/arginine-rich splicing factor 1 (SRSF1) which has roles in alternative splicing. The co-chromatin immunoprecipitation of HDAC1/2 and SRSF1 to the gene body was RNA-dependent. Inhibition of HDAC activity and knockdown of HDAC1, HDAC2 or SRSF1 showed that these proteins were involved in alternative splicing of MCL1. HDAC1/2 and KAT2B were associated with nascent pre-mRNA in general and with MCL1 pre-mRNA specifically. Inhibition of HDAC activity increased the occupancy of KAT2B and acetylation of H3 and H4 of the H3K4 methylated alternative MCL1 exon 2 nucleosome. Thus, nonphosphorylated HDAC1/2 is recruited to pre-mRNA by splicing factors to act at the RNA level with KAT2B and other KATs to catalyze dynamic histone acetylation of the MCL1 alternative exon and alter the splicing of MCL1 pre-mRNA.     

Mitochondrial morphodynamics alteration induced by influenza virus infection as a new antiviral strategy

Influenza virus infections are major public health threats due to their high rates of morbidity and mortality. Upon influenza virus entry, host cells experience modifications of endomembranes, including those used for virus trafficking and replication. Here we report that influenza virus infection modifies mitochondrial morphodynamics by promoting mitochondria elongation and altering endoplasmic reticulum-mitochondria tethering in host cells. Expression of the viral RNA recapitulates these modifications inside cells. Virus induced mitochondria hyper-elongation was promoted by fission associated protein DRP1 relocalization to the cytosol, enhancing a pro-fusion status. We show that altering mitochondrial hyper-fusion with Mito-C, a novel pro-fission compound, not only restores mitochondrial morphodynamics and endoplasmic reticulum-mitochondria contact sites but also dramatically reduces influenza replication. Finally, we demonstrate that the observed Mito-C antiviral property is directly connected with the innate immunity signaling RIG-I complex at mitochondria. Our data highlight the importance of a functional interchange between mitochondrial morphodynamics and innate immunity machineries in the context of influenza viral infection.