Highly modular protein micropatterning sheds light on the role of clathrin-mediated endocytosis for the quantitative analysis of protein-protein interactions in live cells

Protein micropatterning is a powerful tool for spatial arrangement of transmembrane and intracellular proteins in living cells. The restriction of one interaction partner (the bait, e.g., the receptor) in regular micropatterns within the plasma membrane and the monitoring of the lateral distribution of the bait’s interaction partner (the prey, e.g., the cytosolic downstream molecule) enables the in-depth examination of protein-protein interactions in a live cell context. This study reports on potential pitfalls and difficulties in data interpretation based on the enrichment of clathrin, which is a protein essential for clathrin-mediated receptor endocytosis. Using a highly modular micropatterning approach based on large-area micro-contact printing and streptavidin-biotin-mediated surface functionalization, clathrin was found to form internalization hotspots within the patterned areas, which, potentially, leads to unspecific bait/prey protein co-recruitment. We discuss the consequences of clathrin-coated pit formation on the quantitative analysis of relevant protein-protein interactions, describe controls and strategies to prevent the misinterpretation of data, and show that the use of DNA-based linker systems can lead to the improvement of the technical platform

Micropatterning of Plasma Membrane Proteins to Analyze Raft Localization in Living Cells

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Cholesterol Slows down the Lateral Mobility of an Oxidized Phospholipid in a Supported Lipid Bilayer

We investigated the mobility and phase-partitioning of the fluorescent oxidized phospholipid analogue 1-palmitoyl-2-glutaroyl-sn-glycero-3-phospho-N-Alexa647-ethanolamine (PGPE-Alexa647) in supported lipid bilayers. Compared to the conventional phospholipid dihexadecanoylphosphoethanolamine (DHPE)-Bodipy we found consistently higher diffusion constants. The effect become dramatic when immobile obstacles were inserted into the bilayer. which essentially blocked the diffusion of DHPE-Bodipy but hardly influenced the movements of PGPE-Alexa647. In a supported lipid bilayer made of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the differences in probe mobility leveled off with increasing cholesterol content. Using coarse-grained molecular dynamics simulations, we could ascribe this effect to increased interactions between the oxidized phospholipid and the membrane matrix, concomitant with a translation in the headgroup position of the oxidized phospholipid: at zero cholesterol content, its headgroup is shifted to the outside of the DOPC headgroup region, whereas increasing cholesterol concentrations pulls the headgroup into the bilayer plane

Mrs2p Forms a High Conductance Mg2+ Selective Channel in Mitochondria

Members of the CorA-Mrs2-Alr1 superfamily of Mg2+ transporters are ubiquitous among pro- and eukaryotes. The crystal structure of a bacterial CorA protein has recently been solved, but the mode of ion transport of this protein family remained obscure. Using single channel patch clamping we unequivocally show here that the mitochondrial Mrs2 protein forms a Mg2+-selective channel of high conductance (155 pS). It has an open probability of ∼60% in the absence of Mg2+ at the matrix site, which decreases to ∼20% in its presence. With a lower conductance (∼45 pS) the Mrs2 channel is also permeable for Ni2+, whereas no permeability has been observed for either Ca2+, Mn2+, or Co2+. Mutational changes in key domains of Mrs2p are shown either to abolish its Mg2+ transport or to change its characteristics toward more open and partly deregulated states. We conclude that Mrs2p forms a high conductance Mg2+ selective channel that controls Mg2+ influx into mitochondria by an intrinsic negative feedback mechanism

Multi-level suppression of receptor-PI3K-mTORC1 by fatty acid synthase inhibitors is crucial for their efficacy against ovarian cancer cells

Receptor-PI3K-mTORC1 signaling and fatty acid synthase (FASN)-regulated lipid biosynthesis harbor numerous drug targets and are molecularly connected. We hypothesize that unraveling the mechanisms of pathway cross-talk will be useful for designing novel co-targeting strategies for ovarian cancer (OC). The impact of receptor-PI3K-mTORC1 onto FASN is already well-characterized. However, reverse actions–from FASN towards receptor-PI3K-mTORC1–are still elusive. We show that FASN-blockade impairs receptor-PI3K-mTORC1 signaling at multiple levels. Thin-layer chromatography and MALDI-MS/MS reveals that FASN-inhibitors (C75, G28UCM) augment polyunsaturated fatty acids and diminish signaling lipids diacylglycerol (DAG) and phosphatidylinositol 3,4,5-trisphosphate (PIP3) in OC cells (SKOV3, OVCAR-3, A2780, HOC-7). Western blotting and micropatterning demonstrate that FASN-blockers impair phosphorylation/expression of EGF-receptor/ERBB/HER and decrease GRB2–EGF-receptor recruitment leading to PI3K-AKT suppression. FASN-inhibitors activate stress response-genes HIF-1α-REDD1 (RTP801/DIG2/DDIT4) and AMPKα causing mTORC1- and S6-repression. We conclude that FASN-inhibitor-mediated blockade of receptor-PI3K-mTORC1 occurs due to a number of distinct but cooperating processes. Moreover, decrease of PI3K-mTORC1 abolishes cross-repression of MEK-ERK causing ERK activation. Consequently, the MEK-inhibitor selumetinib/AZD6244, in contrast to the PI3K/mTOR-inhibitor dactolisib/NVP-BEZ235, increases growth inhibition when given together with a FASN-blocker. We are the first to provide deep insight on how FASN-inhibition blocks ERBB-PI3K-mTORC1 activity at multiple molecular levels. Moreover, our data encourage therapeutic approaches using FASN-antagonists together with MEK-ERK-inhibitors

Bi-allelic Variants in TKFC Encoding Triokinase/FMN Cyclase Are Associated with Cataracts and Multisystem Disease

We report an inborn error of metabolism caused by TKFC deficiency in two unrelated families. Rapid trio genome sequencing in family 1 and exome sequencing in family 2 excluded known genetic etiologies, and further variant analysis identified rare homozygous variants in TKFC. TKFC encodes a bifunctional enzyme involved in fructose metabolism through its glyceraldehyde kinase activity and in the generation of riboflavin cyclic 4′,5′-phosphate (cyclic FMN) through an FMN lyase domain. The TKFC homozygous variants reported here are located within the FMN lyase domain. Functional assays in yeast support the deleterious effect of these variants on protein function. Shared phenotypes between affected individuals with TKFC deficiency include cataracts and developmental delay, associated with cerebellar hypoplasia in one case. Further complications observed in two affected individuals included liver dysfunction and microcytic anemia, while one had fatal cardiomyopathy with lactic acidosis following a febrile illness. We postulate that deficiency of TKFC causes disruption of endogenous fructose metabolism leading to generation of by-products that can cause cataract. In line with this, an affected individual had mildly elevated urinary galactitol, which has been linked to cataract development in the galactosemias. Further, in light of a previously reported role of TKFC in regulating innate antiviral immunity through suppression of MDA5, we speculate that deficiency of TKFC leads to impaired innate immunity in response to viral illness, which may explain the fatal illness observed in the most severely affected individual

Pharmacological interventions for the management of children and adolescents living with obesity – An update of a Cochrane systematic review with meta-analyses

Importance: The effectiveness of anti-obesity medications for children and adolescents is unclear. Objective: To update the evidence on the benefits and harms of anti-obesity medication. Data sources: Cochrane CENTRAL, MEDLINE, ClinicalTrials.gov, WHO ICTRP (1/1/16-17/3/23). Study selection: Randomized controlled trials ≥6-months in people <19years living with obesity. Data extraction and Synthesis: Screening, data extraction, quality assessment conducted in duplicate, independently. Main Outcomes and Measures: Body Mass Index (BMI): 95th percentile BMI, adverse events, quality of life. Results: Thirty-five trials (N=4,331), follow-up: 6-24 months; age: 8.8-16.3 years; BMI: 26.2-41.7kg/m2. Moderate certainty evidence demonstrated a -1.71 (95% confidence interval [CI]: -2.27 to -1.14)-unit BMI reduction, ranging from -0.8 to -5.9 units between individual drugs with Semaglutide producing the largest reduction of -5.88 kg/m2 (95% CI: -6.99 to -4.77, N = 201). Drug type explained ~44% of heterogeneity. Low certainty evidence demonstrated reduction in 95th percentile BMI: -11.88 percentage points (95% CI: -18.43 to -5.30, N = 668). Serious adverse events and study discontinuation due to adverse events, did not differ between medications and comparators, but medication dose adjustments were higher compared to comparator (10.6% vs 1.7%; RR = 3.74 [95% CI: 1.51 to 9.26], I2 = 15%), regardless of approval status. There was a trend towards improved quality of life. Evidence gaps exist for children, psychosocial outcomes, comorbidities, and weight loss maintenance. Conclusions and Relevance: Anti-obesity medications in addition to behaviour-change, improves BMI but may require dose adjustment, with 1 in 100 adolescents experiencing a serious adverse event

Pharmacological interventions for the management of children and adolescents living with obesity - An update of a Cochrane systematic review with meta-analyses

Importance The effectiveness of anti-obesity medications for children and adolescents is unclear. Objective To update the evidence on the benefits and harms of anti-obesity medication. Data Sources Cochrane CENTRAL, MEDLINE, ClinicalTrials.gov and WHO ICTRP (1/1/16–17/3/23). Study Selection Randomized controlled trials ≥6 months in people <19 years living with obesity. Data Extraction and Synthesis Screening, data extraction and quality assessment conducted in duplicate, independently. Main Outcomes and Measures Body mass index (BMI): 95th percentile BMI, adverse events and quality of life. Results Thirty-five trials (N = 4331), follow-up: 6–24 months; age: 8.8–16.3 years; BMI: 26.2–41.7 kg/m2. Moderate certainty evidence demonstrated a −1.71 (95% confidence interval [CI]: −2.27 to −1.14)-unit BMI reduction, ranging from −0.8 to −5.9 units between individual drugs with semaglutide producing the largest reduction of −5.88 kg/m2 (95% CI: −6.99 to −4.77, N = 201). Drug type explained ~44% of heterogeneity. Low certainty evidence demonstrated reduction in 95th percentile BMI: −11.88 percentage points (95% CI: −18.43 to −5.30, N = 668). Serious adverse events and study discontinuation due to adverse events did not differ between medications and comparators, but medication dose adjustments were higher compared to comparator (10.6% vs 1.7%; RR = 3.74 [95% CI: 1.51 to 9.26], I2 = 15%), regardless of approval status. There was a trend towards improved quality of life. Evidence gaps exist for children, psychosocial outcomes, comorbidities and weight loss maintenance. Conclusions and Relevance Anti-obesity medications in addition to behaviour change improve BMI but may require dose adjustment, with 1 in 100 adolescents experiencing a serious adverse event