The understanding that organelles are not floating in the cytosol, but rather held in an organized yet dynamic interplay through membrane contact sites, is altering the way we grasp cell biological ...phenomena. However, we still have not identified the entire repertoire of contact sites, their tethering molecules and functions. To systematically characterize contact sites and their tethering molecules here we employ a proximity detection method based on split fluorophores and discover four potential new yeast contact sites. We then focus on a little-studied yet highly disease-relevant contact, the Peroxisome-Mitochondria (PerMit) proximity, and uncover and characterize two tether proteins: Fzo1 and Pex34. We genetically expand the PerMit contact site and demonstrate a physiological function in β-oxidation of fatty acids. Our work showcases how systematic analysis of contact site machinery and functions can deepen our understanding of these structures in health and disease.
The integral membrane protein ATG9A plays a key role in autophagy. It displays a broad intracellular distribution and is present in numerous compartments, including the plasma membrane (PM). The ...reasons for the distribution of ATG9A to the PM and its role at the PM are not understood. Here, we show that ATG9A organizes, in concert with IQGAP1, components of the ESCRT system and uncover cooperation between ATG9A, IQGAP1 and ESCRTs in protection from PM damage. ESCRTs and ATG9A phenocopied each other in protection against PM injury. ATG9A knockouts sensitized the PM to permeabilization by a broad spectrum of microbial and endogenous agents, including gasdermin, MLKL and the MLKL-like action of coronavirus ORF3a. Thus, ATG9A engages IQGAP1 and the ESCRT system to maintain PM integrity.
Lipid droplets store neutral lipids, primarily triacylglycerol and steryl esters. Seipin plays a role in lipid droplet biogenesis and is thought to determine the site of lipid droplet biogenesis and ...the size of newly formed lipid droplets. Here we show a seipin-independent pathway of lipid droplet biogenesis. In silico and in vitro experiments reveal that retinyl esters have the intrinsic propensity to sequester and nucleate in lipid bilayers. Production of retinyl esters in mammalian and yeast cells that do not normally produce retinyl esters causes the formation of lipid droplets, even in a yeast strain that produces only retinyl esters and no other neutral lipids. Seipin does not determine the size or biogenesis site of lipid droplets composed of only retinyl esters or steryl esters. These findings indicate that the role of seipin in lipid droplet biogenesis depends on the type of neutral lipid stored in forming droplets.
Many different tissues and cell types exhibit regulated secretion of lipoprotein lipase (LPL). However, the sorting of LPL in the trans Golgi network has not, hitherto, been understood in detail. ...Here, we characterize the role of SorLA (officially known as SorLA-1 or sortilin-related receptor) in the intracellular trafficking of LPL. We found that LPL bound to SorLA under neutral and acidic conditions, and in cells this binding mainly occurred in vesicular structures. SorLA expression changed the subcellular distribution of LPL so it became more concentrated in endosomes. From the endosomes, LPL was further routed to the lysosomes, which resulted in a degradation of newly synthesized LPL. Consequently, an 80% reduction of LPL activity was observed in cells that expressed SorLA. By analogy, SorLA regulated the vesicle-like localization of LPL in primary neuronal cells. Thus, LPL binds to SorLA in the biosynthetic pathway and is subsequently transported to endosomes. As a result of this SorLA mediated-transport, newly synthesized LPL can be routed into specialized vesicles and eventually sent to degradation, and its activity thereby regulated.
Protein therapeutics have a major role in medicine in that they are used to treat diverse pathologies. Their three-dimensional structures not only offer higher specificity and lower toxicity than ...small organic compounds but also make them less stable, limiting their in vivo half-life. Protein analogues obtained by recombinant DNA technology or by chemical modification and/or the use of drug delivery vehicles has been adopted to improve or modulate the in vivo pharmacological activity of proteins. Nevertheless, strategies to improve the shelf-life of protein pharmaceuticals have been less explored, which has challenged the preservation of their activity. Herein, we present a methodology that simultaneously increases the stability of proteins and modulates the release profile, and implement it with human insulin as a proof of concept. Two novel thermally stable insulin composite crystal formulations intended for the therapeutic treatment of diabetes are reported. These composite crystals have been obtained by crystallizing insulin in agarose and fluorenylmethoxycarbonyl-dialanine (Fmoc-AA) hydrogels. This process affords composite crystals, in which hydrogel fibers are occluded. The insulin in both crystalline formulations remains unaltered at 50 °C for 7 days. Differential scanning calorimetry, high-performance liquid chromatography, mass spectrometry, and in vivo studies have shown that insulin does not degrade after the heat treatment. The nature of the hydrogel modifies the physicochemical properties of the crystals. Crystals grown in Fmoc-AA hydrogel are more stable and have a slower dissolution rate than crystals grown in agarose. This methodology paves the way for the development of more stable protein pharmaceuticals overcoming some of the existing limitations.
Phosphatidylcholine (PC) is an abundant membrane lipid component in most eukaryotes, including yeast, and has been assigned multiple functions in addition to acting as building block of the lipid ...bilayer. Here, by isolating S. cerevisiae suppressor mutants that exhibit robust growth in the absence of PC, we show that PC essentiality is subject to cellular evolvability in yeast. The requirement for PC is suppressed by monosomy of chromosome XV or by a point mutation in the ACC1 gene encoding acetyl‐CoA carboxylase. Although these two genetic adaptations rewire lipid biosynthesis in different ways, both decrease Acc1 activity, thereby reducing average acyl chain length. Consistently, soraphen A, a specific inhibitor of Acc1, rescues a yeast mutant with deficient PC synthesis. In the aneuploid suppressor, feedback inhibition of Acc1 through acyl‐CoA produced by fatty acid synthase (FAS) results from upregulation of lipid synthesis. The results show that budding yeast regulates acyl chain length by fine‐tuning the activities of Acc1 and FAS and indicate that PC evolved by benefitting the maintenance of membrane fluidity.
SYNOPSIS
Saccharomyces cerevisiae suppressor mutants overcoming choline auxotrophy allow growth in the absence of the major membrane lipid phosphatidylcholine (PC). This study reveals that the interplay between acetyl‐CoA carboxylase (Acc1) and fatty acid synthase (FAS), which regulates lipid acyl chain length, renders PC redundant in such mutant.
Most PC‐free choline auxotrophy suppressors are 2n‐1 aneuploids lacking one copy of chromosome XV.
Rare diploid suppressor strains contain a homozygous point mutation in the ACC1 gene encoding acetyl‐CoA carboxylase.
Aneuploid suppressors rely on feed‐back inhibition of Acc1 by FAS‐derived acyl‐CoA, resulting from up‐regulation of lipid synthesis.
Inhibition of Acc1 activity is crucial for suppression by reducing average lipid acyl chain length to maintain membrane fluidity.
The interplay between acetyl‐CoA carboxylase and fatty acid synthase regulates lipid acyl chain length, and renders phosphatidylcholine redundant in Saccharomyces cerevisiae.
Metabolic function and architecture of mitochondria are intimately linked. More than 60 years ago, cristae were discovered as characteristic elements of mitochondria that harbor the protein complexes ...of oxidative phosphorylation, but how cristae are formed, remained an open question. Here we present experimental results obtained with yeast that support a novel hypothesis on the existence of two molecular pathways that lead to the generation of lamellar and tubular cristae. Formation of lamellar cristae depends on the mitochondrial fusion machinery through a pathway that is required also for homeostasis of mitochondria and mitochondrial DNA. Tubular cristae are formed via invaginations of the inner boundary membrane by a pathway independent of the fusion machinery. Dimerization of the F
F
-ATP synthase and the presence of the MICOS complex are necessary for both pathways. The proposed hypothesis is suggested to apply also to higher eukaryotes, since the key components are conserved in structure and function throughout evolution.
Locally advanced colon cancer is a high-risk condition for tumour recurrence with poor survival. The current treatment is surgery followed by adjuvant chemotherapy based on fluoropyrimidines and ...oxaliplatin. This approach has improved the oncological outcomes on this population, however the mucinous condition has not been studied in depth and although the evidence is weak, it is thought to have a worse response to systemic chemotherapy. The CHEMUCCA study aims to answer this question.
To evaluate the effectiveness of adjuvant systemic chemotherapy using the disease-free survival for stage II and III mucinous colon cancer who underwent surgical resection plus systemic adjuvant chemotherapy vs. surgery alone.
Retrospective analytical study including patients diagnosed with high-risk stage II and stage III colon cancer, treated between 2010 and 2021, with a minimum follow-up of 3 years. Demographic variables and tumour features were analysed. The primary endpoint was disease-free survival. Log rank test and Cox regression were used.
Of 1134 patients with high-risk stage II and III colon cancer disease, 206 (18,17 %) had mucinous histology and 928 (81,83 %) had non-mucinous histology. 708 patients who received adjuvant chemotherapy, 129 (62,62 %) in mucinous group and 579 (62,39 %) in the non-mucinous group. Adjuvant systemic chemotherapy in stage II and III mucinous colon cancer improved the DFS (HR = 0.58 95 % CI 0.37−0.91; p = 0,017). However, in a stratified analysis, patients with high-risk stage II mucinous colon cancer showed no benefit with this approach (HR = 0.4541 95 % CI 0.19−1.03; p = 0.06).
Adjuvant chemotherapy has demonstrated to be effective in locally advanced mucinous colorectal cancer improving the oncological outcomes. However, this benefit could be diminished in high-risk stage II mucinous colon cancer patients. The administration of adjuvant chemotherapy on this patient's sub-group must be balanced according to risk versus benefits.
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