BAG3 induction is required to mitigate proteotoxicity via selective autophagy following inhibition of constitutive protein degradation pathways

Protein quality control systems (PQC), i.e. UPS and aggresome-autophagy pathway, have been suggested to be promising targets in cancer therapy: simultaneous pharmacological inhibition of both pathways have shown increase efficacy in various tumors such as ovarian and colon carcinoma. Here, we investigate the effect of concomitant inhibition of 26S proteasome by FDA approved inhibitor Bortezomib, and HDAC6, as key mediator of the aggresome/autophagy system, by the highly specific inhibitor ST80 in Rhabdomyosarcoma (RMS) cell lines. We demonstrated that simultaneous inhibition of 26S proteasome and selective aggresome/autophagy pathway significantly increases apoptosis in all tested RMS cell lines. Interestingly, we observed that a subpopulation of RMS cells was able to survive the co-treatment and, upon drug removal, to recover similarly to untreated cells. In this study, we identified co-chaperone BAG3 as the key mediator of this recovery: BAG3 is transcriptionally up-regulated specifically in the ST80/Bortezomib surviving cells and mediates clearance of cytotoxic protein aggregates by selective autophagy. Impairment of the autophagic pathway during the recovery phase, both by conditional knock down of ATG7 or by inhibition of lysosomal degradation by BafylomicinA1, triggers accumulation of insoluble protein aggregates, loss of cell recovery and cell death similarly to stable short harpin mRNA BAG3 knock. Our results are the first demonstration that BAG3 mediated selective autophagy is engaged to cope with proteotoxicity induced by simultaneous inhibition of constitutive PQC systems in cancer cell lines during cell recovery. Moreover our data give new insight in regulation of constitutive and on demand PQC mechanisms pointing to BAG3 as a promising target in RMS therapy

Redox Mediation at 11-Mercaptoundecanoic Acid Self-Assembled Monolayers on Gold

Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and digital simulation techniques were used to investigate quantitatively the mechanism of electron transfer (ET) through densely packed and well-ordered self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid on gold, either pristine or modified by physically adsorbed glucose oxidase (GOx). In the presence of ferrocenylmethanol (FcMeOH) as a redox mediator, ET kinetics involving either solution-phase hydrophilic redox probes such as [Fe(CN)6]3-/4- or surface-immobilized GOx is greatly accelerated: [Fe(CN)6]3-/4- undergoes diffusion-controlled ET, while the enzymatic electrochemical conversion of glucose to gluconolactone is efficiently sustained by FcMeOH. Analysis of the results, also including the digital simulation of CV and EIS data, showed the prevalence of an ET mechanism according to the so-called membrane model that comprises the permeation of the redox mediator within the SAM and the intermolecular ET to the redox probe located outside the monolayer. The analysis of the catalytic current generated at the GOx/SAM electrode in the presence of glucose and FcMeOH allowed the high surface protein coverage suggested by X-ray photoelectron spectroscopy (XPS) measurements to be confirmed.

A simple model of the electrostatic environment around the catalytic center of the ribosome and its significance for the elongation kinetics

editorial reviewedThe central function of the large subunit of the ribosome is to catalyze peptide bond formation. This biochemical reaction is conducted at the peptidyl transferase center (PTC). Experimental evidence shows that the catalytic activity is affected by the electrostatic environment around the peptidyl transferase center. Here, we set up a minimal geometrical model fitting the available X-ray solved structures of the ribonucleoproteic cavity around the catalytic center of the large subunit of the ribosome. The purpose of this phenomenological model is to estimate quantitatively the electrostatic potential and electric field that are experienced during the peptidyl transfer reaction. At least two reasons motivate the need for developing this quantification. First, we inquire whether the electric field in this particular catalytic environment, made only of nucleic acids, is of the same order of magnitude as the one prevailing in catalytic centers of the proteic enzymes counterparts. Second, the protein synthesis rate is dependent on the nature of the amino acid sequentially incorporated in the nascent chain. The activation energy of the catalytic reaction and its detailed kinetics are shown to be dependent on the mechanical work exerted on the amino acids by the electric field, especially when one of the four charged amino acid residues (R, K, E, D) is newly incorporated in the nascent chain. Physical values of the electric field provide quantitative knowledge of mechanical work, activation energy and rate of the peptide bond formation catalyzed by the ribosome. We show that our theoretical calculations are consistent with two independent sets of previously published experimental results. Experimental results for E.coli in the minimal case of the dipeptide bond formation when puromycin is used as the final amino acid acceptor strongly support our theoretically derived reaction time courses. Experimental Ribo-seq results on S. cerevisiae and E.coli comparing the residence time distribution of ribosomes upon specific codons are also well accounted for by our theoretical calculations. Our interpretation of these results sheds light on the functional role of the electrostatic profile around the PTC and its impact on the ribosome elongation cycle

Belgium

The impact of ribosome exit tunnel electrostatics on the protein elongation rate or on forces acting upon the nascent polypeptide chain are currently not fully elucidated. In the past, researchers have measured the electrostatic potential inside the ribosome polypeptide exit tunnel at a limited number of spatial points, at least in rabbit reticulocytes. Here we present a basic electrostatic model of the exit tunnel of the ribosome, providing a quantitative physical description of the tunnel interaction with the nascent proteins at all centro-axial points inside the tunnel. We show that a strong electrostatic screening is due to water molecules (not mobile ions) attracted to the ribosomal nucleic acid phosphate moieties buried in the immediate vicinity of the tunnel wall. We also show how the tunnel wall components and local ribosomal protein protrusions impact on the electrostatic potential profile and impede charged amino acid residues from progressing through the tunnel, affecting the elongation rate in a range of −40% to +85% when compared to the average elongation rate. The time spent by the ribosome to decode the genetic encrypted message is constrained accordingly. We quantitatively derive, at single-residue resolution, the axial forces acting on the nascent peptide from its particular sequence embedded in the tunnel. The model sheds light on how the experimental data point measurements of the potential are linked to the local structural chemistry of the inner wall, shape, and size of the tunnel. The model consistently connects experimental observations coming from different fields in molecular biology, x-ray crystallography, physical chemistry, biomechanics, and synthetic and multiomics biology. Our model should be a valuable tool to gain insight into protein synthesis dynamics, translational control, and the role of the ribosome's mechanochemistry in the cotranslational protein folding.FNRS-FWO EOS Grant No. 30480119 (Join-t-against-Osteoarthritis); WELBIO CR2017S02 (THERAtRAME);ERC grant agreement n°772418 (INSITE

A simple geometrical model of the electrostatic environment around the catalytic center of the ribosome and its significance for the elongation cycle kinetics

peer reviewedThe central function of the large subunit of the ribosome is to catalyze peptide bond formation. This biochemical reaction is conducted at the peptidyl transferase center (PTC). Experimental evidence shows that the catalytic activity is affected by the electrostatic environment around the peptidyl transferase center. Here, we set up a minimal geometrical model fitting the available x-ray solved structures of the ribonucleic cavity around the catalytic center of the large subunit of the ribosome. The purpose of this phenomenological model is to estimate quantitatively the electrostatic potential and electric field that are experienced during the peptidyl transfer reaction. At least two reasons motivate the need for developing this quantification. First, we inquire whether the electric field in this particular catalytic environment, made only of nucleic acids, is of the same order of magnitude as the one prevailing in catalytic centers of the proteic enzymes counterparts. Second, the protein synthesis rate is dependent on the nature of the amino acid sequentially incorporated in the nascent chain. The activation energy of the catalytic reaction and its detailed kinetics are shown to be dependent on the mechanical work exerted on the amino acids by the electric field, especially when one of the four charged amino acid residues (R, K, E, D) has previously been incorporated at the carboxy-terminal end of the peptidyl-tRNA. Physical values of the electric field provide quantitative knowledge of mechanical work, activation energy and rate of the peptide bond formation catalyzed by the ribosome. We show that our theoretical calculations are consistent with two independent sets of previously published experimental results. Experimental results for E.coli in the minimal case of the dipeptide bond formation when puromycin is used as the final amino acid acceptor strongly support our theoretically derived reaction time courses. Experimental Ribo-Seq results on E. coli and S. cerevisiae comparing the residence time distribution of ribosomes upon specific codons are also well accounted for by our theoretical calculations. The statistical queueing time theory was used to model the ribosome residence time per codon during nascent protein elongation and applied for the interpretation of the Ribo-Seq data. The hypo-exponential distribution fits the residence time observed distribution of the ribosome on a codon. An educated deconvolution of this distribution is used to estimate the rates of each elongation step in a codon specific manner. Our interpretation of all these results sheds light on the functional role of the electrostatic profile around the PTC and its impact on the ribosome elongation cycle

Wobble tRNA modification and hydrophilic amino acid patterns dictate protein fate.

peer reviewedRegulation of mRNA translation elongation impacts nascent protein synthesis and integrity and plays a critical role in disease establishment. Here, we investigate features linking regulation of codon-dependent translation elongation to protein expression and homeostasis. Using knockdown models of enzymes that catalyze the mcm(5)s(2) wobble uridine tRNA modification (U(34)-enzymes), we show that gene codon content is necessary but not sufficient to predict protein fate. While translation defects upon perturbation of U(34)-enzymes are strictly dependent on codon content, the consequences on protein output are determined by other features. Specific hydrophilic motifs cause protein aggregation and degradation upon codon-dependent translation elongation defects. Accordingly, the combination of codon content and the presence of hydrophilic motifs define the proteome whose maintenance relies on U(34)-tRNA modification. Together, these results uncover the mechanism linking wobble tRNA modification to mRNA translation and aggregation to maintain proteome homeostasis

Induced transdifferentiation of human B-leukemia/lymphoma cell lines and inhibition of leukemogenicity

B-cell malignancies encompass a wide variety of distinct diseases including Non Hodgkin lymphoma (NHL) and leukemia. Currently, chemotherapy, radiation and anti-CD20 antibody treatment are the mainstays of B-cell lymphoma and leukemia therapy. However, the fact that a large number of patients are eventually not cured justifies the search for novel and more effective therapeutic approaches. Although induction of differentiation has been shown to be effective in several tumors such as acute promyelocytic leukemia, it has not been tested yet in NHL and leukemia. We therefore hypothesized that transdifferentiation of malignant B cells could be proposed as a novel therapeutic approach. Earlier work of our laboratory demonstrated that the transcription factor C/EBPα could convert immature and mature murine B lineage cells into functional macrophages at high efficiencies. Here we show that the ectopic expression of C/EBPα can likewise induce the conversion of selected human lymphoma and leukemia B-cell lines into macrophages. The reprogrammed cells are functional and quiescent. Importantly, the tumorigenicity of transdifferentiated lymphoma and leukemia cell lines was impaired after transplantation into immunodeficient mice, even when C/EBPα was activated in vivo. In summary, our experiments show for the first time that human cancer cells can be induced to transdifferentiate by C/EBPα into seemingly normal cells at high frequencies, thus proposing transdifferentiation as novel therapeutic approach. In line with this, we believe that the finding of a small molecule that mimics C/EBPα overexpression will open new horizons for the cure of patients affected by B cell malignancies.Las neoplasias malignas de células B abarcan una amplia variedad de enfermedades diferentes, incluyendo el linfoma no Hodgkin (LNH) y leucemia. Actualmente, la quimioterapia, la radiación y el tratamiento con anticuerpos anti-CD20 son los pilares de la terapia contra el linfoma y la leucemia de células B. Sin embargo, el hecho de que un gran porcentaje de pacientes no se cura con estos tratamientos, justifica la búsqueda de nuevas terapias más eficaces. Aunque la inducción de la diferenciación ha demostrado ser eficaz en el tratamiento de varios tumores tales como la leucemia promielocítica aguda, esta técnica no se ha probado aún en el tratamiento del LNH o de la leucemia. Por lo tanto, la transdiferenciación de las células B malignas podría ser propuesta como un nuevo enfoque terapéutico. Trabajos anteriores de nuestro laboratorio han demostrado que el factor de transcripción C/EBPα puede convertir células de linaje B murinas inmaduras y maduras en macrófagos funcionales con una alta eficiencia. En este trabajo mostramos que la expresión ectópica de C/EBPα puede inducir la conversión de ciertas líneas de linfoma y leucemia humana en macrófagos. Las células reprogramadas son funcionales y quiescientes. Es importante destacar que la tumorigenicidad de linfoma transdiferenciados y líneas celulares de leucemia se vio afectada después del trasplante en ratones inmunodeficientes, incluso cuando C/EBPα se activó in vivo. En resumen, nuestros experimentos muestran por primera vez que las células de cáncer humano pueden ser inducidas por C/EBPα a transdifferenciarse en células aparentemente normales con una alta frecuencia, proponiendo así la transdiferenciación como nuevo enfoque terapéutico. En línea con esto, creemos que el hallazgo de una pequeña molécula que sea capaz de imitar la sobreexpresión de C/EBPα abrirá nuevos horizontes para la cura de los pacientes afectados por tumores malignos de células B