A study of the SNARE protein syntaxin 16 and its role in the intracellular trafficking of glucose transporter GLUT4 in 3T3-L1 adipocytes
Notice bibliographique
Résumé
In muscle and adipose tissue insulin promotes glucose uptake by stimulating the translocation of the glucose transporter GLUT4 from an intracellular location to the plasma membrane. This exocytic delivery of GLUT4 to the plasma membrane is fundamental for the maintenance of blood glucose homeostasis. Individuals with insulin resistance or type II diabetes exhibit a blunted ability of insulin to stimulate GLUT4 translocation, and, as a result, a decreased rate of insulin stimulated glucose transport. To design effective therapies we require a clear understanding of the molecular basis of intracellular GLUT4 trafficking. Recent studies support a model in which the intracellular GLUT4 itinerary involves two intracellular cycles. In the basal state, GLUT4 recycles between the PM and endosomes in the fast recycling endosomal system. However, unique sequences within GLUT4 cause a large population to be sorted away from the endosomal system, into a slowly recycling intracellular pathway between endosomes and the TGN. This pathway involves the sorting of GLUT4 into unique storage vesicles, (GLUT4 storage vesicles, GSVs) which are mobilised in response to insulin, and are responsible for the majority of GLUT4 that is delivered to the cell surface in response to insulin. The intracellular sorting of GLUT4 is therefore essential to direct GLUT4 into the insulin-responsive compartment and to effectively sequester GLUT4 from the cell surface in the basal state. However, the molecules responsible for regulating this intracellular sorting pathway remain largely unknown. Previous studies have implicated the TGN localised t-SNARE, STX16, in GLUT4 trafficking in 3T3-L1 adipocytes. STX16 is a phosphoprotein in these cells and phosphorylation is decreased in response to acute insulin stimulation. This study aimed to elucidate the role, if any, of STX16 in GLUT4 trafficking, and to determine whether phosphorylation was responsible for the regulation of this process. In this study, experiments to identify the exact site of insulin-regulated phosphorylation were carried out in HEK 293 cells and suggest that STX16 phosphorylation may be specific to adipocytes. Immunoprecipitation studies revealed the existence of a STX16 containing SNARE complex in 3T3-L1 adipocytes with the t-SNAREs STX6 and Vtila; however, this SNARE complex does not appear to be regulated by insulin. These studies also suggest that STX16 does not bind to its cognate SM protein, mVps45, when part of this SNARE complex, either in the presence or absence of insulin. Recombinant adenoviruses were generated to express wild-type STX16 and STX16 mutants in 3T3-L1 adipocytes to assess their effects on glucose transport. Expression of these STX16 mutants proved problematic due to a property inherent in STX16, which requires stabilisation by its cognate SM protein, mVps45. It appears that STX16 expressed in excess of mVps45 is subject to proteasomal degradation, since expression could be dramatically increased when proteasome function was inhibited. One mutant, STX16cyt, constituted the dominant negative cytosolic domain of STX16 and was expressed in adipocytes to perturb endogenous STX16 function. Expression of STX16cyt significantly slowed the endocytic retrieval of GLUT4 following insulin- withdrawal. In contrast, expression of STX16cyt had no effect on the secretion of an adipocyte-derived adipokine, ACRP30. In a complementary approach, endogenous STX16 was knocked down by > 90 % using a specific Morpholino Antisense Oligonucleotide. 3T3-L1 adipocytes depleted of STX16 in this way showed a significant decrease in insulin- stimulated glucose transport. This corresponded with ~ 30 % decrease in cellular GLUT4 levels. These data were rationalised within a model in which STX16 functions to sequester GLUT4 from the PM in the basal state in a step which involves the intracellular sorting of GLUT4 from the fast cycling endosomal system into the slowly recycling intracellular pool of which GSVs are part. In cells depleted of STX16, this pathway is blocked and GLUT4 appears to be directed into a degradative pathway.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,001 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».