CHC22 clathrin recruitment to the early secretory pathway requires two-site interaction with SNX5 and p115.

The two clathrin isoforms, CHC17 and CHC22, mediate separate intracellular transport routes. CHC17 performs endocytosis and housekeeping membrane traffic in all cells. CHC22, expressed most highly in skeletal muscle, shuttles the glucose transporter GLUT4 from the ERGIC (endoplasmic-reticulum-to-Golgi intermediate compartment) directly to an intracellular GLUT4 storage compartment (GSC), from where GLUT4 can be mobilized to the plasma membrane by insulin.

Neurodevelopmental and synaptic defects in DNAJC6 parkinsonism, amenable to gene therapy.

DNAJC6 encodes auxilin, a co-chaperone protein involved in clathrin-mediated endocytosis (CME) at the presynaptic terminal. Biallelic mutations in DNAJC6 cause a complex, early-onset neurodegenerative disorder characterized by rapidly progressive parkinsonism-dystonia in childhood. The disease is commonly associated with additional neurodevelopmental, neurological and neuropsychiatric features.

Clathrin light chains CLCa and CLCb have non-redundant roles in epithelial lumen formation.

To identify functional differences between vertebrate clathrin light chains (CLCa or CLCb), phenotypes of mice lacking genes encoding either isoform were characterised. Mice without CLCa displayed 50% neonatal mortality, reduced body weight, reduced fertility, and ∼40% of aged females developed uterine pyometra. Mice lacking CLCb displayed a less severe weight reduction phenotype compared with those lacking CLCa and had no survival or reproductive system defects.

Trafficking regulator of GLUT4-1 (TRARG1) is a GSK3 substrate.

Trafficking regulator of GLUT4-1, TRARG1, positively regulates insulin-stimulated GLUT4 trafficking and insulin sensitivity. However, the mechanism(s) by which this occurs remain(s) unclear. Using biochemical and mass spectrometry analyses we found that TRARG1 is dephosphorylated in response to insulin in a PI3K/Akt-dependent manner and is a novel substrate for GSK3.

Antagonistic regulation controls clathrin-mediated endocytosis: AP2 adaptor facilitation vs restraint from clathrin light chains.

Orchestration of a complex network of protein interactions drives clathrin-mediated endocytosis (CME). A central role for the AP2 adaptor complex beyond cargo recognition and clathrin recruitment has emerged in recent years. It is now apparent that AP2 serves as a pivotal hub for protein interactions to mediate clathrin coated pit maturation, and couples lattice formation to membrane deformation.

Ernst Joachim Ungewickell: 1950-2020.

Linton M. Traub and Frances M. Brodsky discuss the life and achievements of Ernst Ungewickell, who passed away on August 19th.

Clathrin light chain diversity regulates membrane deformation in vitro and synaptic vesicle formation in vivo.

Clathrin light chain (CLC) subunits in vertebrates are encoded by paralogous genes and , and both gene products are alternatively spliced in neurons. To understand how this CLC diversity influences neuronal clathrin function, we characterized the biophysical properties of clathrin comprising individual CLC variants for correlation with neuronal phenotypes of mice lacking either CLC-encoding gene. CLC splice variants differentially influenced clathrin knee conformation within assemblies, and clathrin with neuronal CLC mixtures was more effective in membrane deformation than clathrin with single neuronal isoforms nCLCa or nCLCb.

Clathrin's life beyond 40: Connecting biochemistry with physiology and disease.

Understanding of the range and mechanisms of clathrin functions has developed exponentially since clathrin's discovery in 1975. Here, newly established molecular mechanisms that regulate clathrin activity and connect clathrin pathways to differentiation, disease and physiological processes such as glucose metabolism are reviewed. Diversity and commonalities of clathrin pathways across the tree of life reveal species-specific differences enabling functional plasticity in both membrane traffic and cytokinesis.

Building GLUT4 Vesicles: CHC22 Clathrin's Human Touch.

Insulin stimulates glucose transport by triggering regulated delivery of intracellular vesicles containing the GLUT4 glucose transporter to the plasma membrane. This process is defective in diseases such as type 2 diabetes (T2DM). While studies in rodent cells have been invaluable in understanding GLUT4 traffic, evolutionary plasticity must be considered when extrapolating these findings to humans.

CHC22 clathrin mediates traffic from early secretory compartments for human GLUT4 pathway biogenesis.

Glucose transporter 4 (GLUT4) is sequestered inside muscle and fat and then released by vesicle traffic to the cell surface in response to postprandial insulin for blood glucose clearance. Here, we map the biogenesis of this GLUT4 traffic pathway in humans, which involves clathrin isoform CHC22. We observe that GLUT4 transits through the early secretory pathway more slowly than the constitutively secreted GLUT1 transporter and localize CHC22 to the ER-to-Golgi intermediate compartment (ERGIC).

Clathrin light chain A drives selective myosin VI recruitment to clathrin-coated pits under membrane tension.

Clathrin light chains (CLCa and CLCb) are major constituents of clathrin-coated vesicles. Unique functions for these evolutionary conserved paralogs remain elusive, and their role in clathrin-mediated endocytosis in mammalian cells is debated. Here, we find and structurally characterize a direct and selective interaction between CLCa and the long isoform of the actin motor protein myosin VI, which is expressed exclusively in highly polarized tissues.

Lipid Metabolism Links Nutrient-Exercise Timing to Insulin Sensitivity in Men Classified as Overweight or Obese.

Context: Pre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness.

Objective: To assess acute and chronic effects of exercise performed before versus after nutrient ingestion on whole-body and intramuscular lipid utilization and postprandial glucose metabolism.

Design: (1) Acute, randomized, crossover design (Acute Study); (2) 6-week, randomized, controlled design (Training Study).

The AP2 adaptor enhances clathrin coat stiffness.

Deformation of the plasma membrane into clathrin-coated vesicles is a critical step in clathrin-mediated endocytosis and requires the orchestrated assembly of clathrin and endocytic adaptors into a membrane-associated protein coat. The individual role of these membrane-bending and curvature-stabilizing factors is subject to current debate. As such, it is unclear whether the clathrin coat itself is stiff enough to impose curvature and if so, whether this could be effectively transferred to the membrane by the linking adaptor proteins.

Genetic diversity of CHC22 clathrin impacts its function in glucose metabolism.

CHC22 clathrin plays a key role in intracellular membrane traffic of the insulin-responsive glucose transporter GLUT4 in humans. We performed population genetic and phylogenetic analyses of the CHC22-encoding gene, revealing independent gene loss in at least two vertebrate lineages, after arising from gene duplication. All vertebrates retained the paralogous gene encoding CHC17 clathrin, which mediates endocytosis.

CHC22 and CHC17 clathrins have distinct biochemical properties and display differential regulation and function.

Clathrins are cytoplasmic proteins that play essential roles in endocytosis and other membrane traffic pathways. Upon recruitment to intracellular membranes, the canonical clathrin triskelion assembles into a polyhedral protein coat that facilitates vesicle formation and captures cargo molecules for transport. The triskelion is formed by trimerization of three clathrin heavy-chain subunits.

Clathrin light chains' role in selective endocytosis influences antibody isotype switching.

Clathrin, a cytosolic protein composed of heavy and light chain subunits, assembles into a vesicle coat, controlling receptor-mediated endocytosis. To establish clathrin light chain (CLC) function in vivo, we engineered mice lacking CLCa, the major CLC isoform in B lymphocytes, generating animals with CLC-deficient B cells. In CLCa-null mice, the germinal centers have fewer B cells, and they are enriched for IgA-producing cells.

A Distinctive Cytoplasmic Tail Contributes to Low Surface Expression and Intracellular Retention of the Patr-AL MHC Class I Molecule.

Chimpanzees have orthologs of the six fixed, functional human MHC class I genes. But, in addition, the chimpanzee has a seventh functional gene, Patr-AL, which is not polymorphic but contributes substantially to population diversity by its presence on only 50% of MHC haplotypes. The ancestral AL gene emerged long before the separation of human and chimpanzee ancestors and then subsequently and specifically lost function during human evolution, but was maintained in chimpanzees.

Unconventional functions for clathrin, ESCRTs, and other endocytic regulators in the cytoskeleton, cell cycle, nucleus, and beyond: links to human disease.

The roles of clathrin, its regulators, and the ESCRT (endosomal sorting complex required for transport) proteins are well defined in endocytosis. These proteins can also participate in intracellular pathways that are independent of endocytosis and even independent of the membrane trafficking function of these proteins. These nonendocytic functions involve unconventional biochemical interactions for some endocytic regulators, but can also exploit known interactions for nonendocytic functions.

Clathrin light chains are required for the gyrating-clathrin recycling pathway and thereby promote cell migration.

The clathrin light chain (CLC) subunits participate in several membrane traffic pathways involving both clathrin and actin, through binding the actin-organizing huntingtin-interacting proteins (Hip). However, CLCs are dispensable for clathrin-mediated endocytosis of many cargoes. Here we observe that CLC depletion affects cell migration through Hip binding and reduces surface expression of β1-integrin by interference with recycling following normal endocytosis of inactive β1-integrin.

Actin scaffolding by clathrin heavy chain is required for skeletal muscle sarcomere organization.

The ubiquitous clathrin heavy chain (CHC), the main component of clathrin-coated vesicles, is well characterized for its role in intracellular membrane traffic and endocytosis from the plasma membrane (PM). Here, we demonstrate that in skeletal muscle CHC regulates the formation and maintenance of PM-sarcomere attachment sites also known as costameres. We show that clathrin forms large coated lattices associated with actin filaments and the muscle-specific isoform of α-actinin at the PM of differentiated myotubes.

The adaptor protein GULP promotes Jedi-1-mediated phagocytosis through a clathrin-dependent mechanism.

During the development of the peripheral nervous system, the large number of apoptotic neurons generated are phagocytosed by glial precursor cells. This clearance is mediated, in part, through the mammalian engulfment receptor Jedi-1. However, the mechanisms by which Jedi-1 mediates phagocytosis are poorly understood.