Glucose treatment of human pancreatic ß-cells enhances translation of mRNAs involved in energetics and insulin secretion.

Glucose-mediated signaling regulates the expression of a limited number of genes in human pancreatic ß-cells at the transcriptional level. However, it is unclear whether glucose plays a role in posttranscriptional RNA processing or translational control of gene expression. Here, we asked whether glucose affects posttranscriptional steps and regulates protein synthesis in human ß-cell lines. We first showed the involvement of the mTOR pathway in glucose-related signaling. We also used the surface sensing of translation technique, based on puromycin incorporation into newly translated proteins, to demonstrate that glucose treatment increased protein translation. Among the list of glucose-induced proteins, we identified the proconvertase PCSK1, an enzyme involved in the proteolytic conversion of proinsulin to insulin, whose translation was induced within minutes following glucose treatment. We finally performed global proteomic analysis by mass spectrometry to characterize newly translated proteins upon glucose treatment. We found enrichment in proteins involved in translation, glycolysis, TCA metabolism, and insulin secretion. Taken together, our study demonstrates that, although glucose minorly affects gene transcription in human ß-cells, it plays a major role at the translational level.

Enhanced DR5 binding capacity of nanovectorized TRAIL compared to its cytotoxic version by affinity chromatography and molecular docking studies.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis of cancer cells when bound to its cognate receptors, TRAIL-R1 and TRAIL-R2 (DR4 and DR5), without being toxic to healthy cells. Nanovectorized TRAIL (abbreviated as NPT) is 10 to 20 times more efficient than one of the most potent soluble TRAIL used in preclinical studies (His-TRAIL). To determine whether differences in affinity may account for NPT superiority, a thermodynamic study was undertaken to evaluate NPT versus TRAIL binding affinity to DR5. Docking calculations showed that TRAIL in homotrimer configuration was more stable than in heterotrimer, because of the presence of one Zn ion in its structure. Indeed, TRAIL trimers can have head-to-tail orientations when Zn is missing. Altogether these data suggest that TRAIL homotrimer structures are predominant in solution and then are grafted on NPT. When docked to DR5, NPT carrying TRAIL homotrimer leads to a more stable complex than TRAIL monomer-based NPT. To comfort these observations, the extracellular domain of DR5 was immobilized on a chromatographic support using an "in situ" immobilization technique. The determination of the thermodynamic data (enthalpy ∆H° and entropy ∆S°*) of TRAIL and NPT binding to DR5 showed that the binding mechanism was pH dependent. The affinity of NPT to DR5 increased with pH, and the ionized energy was more important for NPT than for soluble TRAIL. Moreover, because of negative values of ∆H° and ∆S°* quantities, we demonstrated that van der Waals and hydrogen bonds governed the strong NPT-DR5 association for pH > 7.4 (as for TRAIL alone). Copyright © 2016 John Wiley & Sons, Ltd.

Glucose controls co-translation of structurally related mRNAs via the mTOR and eIF2 pathways in human pancreatic beta cells.

Pancreatic beta cell response to glucose is critical for the maintenance of normoglycemia. A strong transcriptional response was classically described in rodent models but, interestingly, not in human cells. In this study, we exposed human pancreatic beta cells to an increased concentration of glucose and analysed at a global level the mRNAs steady state levels and their translationalability. Polysome profiling analysis showed an early acute increase in protein synthesis and a specific translation regulation of more than 400 mRNAs, independently of their transcriptional regulation. We clustered the co-regulated mRNAs according to their behaviour in translation in response to glucose and discovered common structural and sequence mRNA features. Among them mTOR- and eIF2-sensitive elements have a predominant role to increase mostly the translation of mRNAs encoding for proteins of the translational machinery. Furthermore, we show that mTOR and eIF2α pathways are independently regulated in response to glucose, participating to a translational reshaping to adapt beta cell metabolism. The early acute increase in the translation machinery components prepare the beta cell for further protein demand due to glucose-mediated metabolism changes.