Constitutive Endocytosis of the Chemokine CX3CL1 Prevents Its Degradation by Cell Surface Metalloproteases
Bibliographic record
Abstract
CX(3)CL1, a chemokine with transmembrane and soluble species, plays a key role in inflammation by acting as both chemoattractant and adhesion molecule. CX(3)CL1 is the only chemokine known to undergo constitutive internalization, raising the possibility that dynamic equilibrium between the endocytic compartment and the plasma membrane critically regulates the availability and processing of CX(3)CL1 at the cell surface. We therefore investigated how transmembrane CX(3)CL1 is internalized. Inhibition of dynamin using a nonfunctional allele or of clathrin using specific small interfering RNA prevented endocytosis of the chemokine in CX(3)CL1-expressing human ECV-304 cells. Perusal of the cytoplasmic domain of CX(3)CL1 revealed two putative adaptor protein-2 (AP-2)-binding motifs. Accordingly, CX(3)CL1 co-localized with AP-2 at the plasma membrane. We generated a mutant allele of CX(3)CL1 lacking the cytoplasmic tail. Deletion of the cytosolic tail precluded internalization of the chemokine. We used site-directed mutagenesis to disrupt AP-2-binding motifs, singly or in combination, which resulted in diminished internalization of CX(3)CL1. Although CX(3)CL1 was present in both superficial and endomembrane compartments, ADAM10 (a disintegrin and metalloprotease 10) and tumor necrosis factor-converting enzyme, the two metalloproteases that cleave CX(3)CL1, localized predominantly to the plasmalemma. Inhibition of endocytosis using the dynamin inhibitor, Dynasore, promoted rapid metalloprotease-dependent shedding of CX(3)CL1 from the cell surface into the surrounding medium. These findings indicate that the cytoplasmic tail of CX(3)CL1 facilitates its constitutive clathrin-mediated endocytosis. Such regulation enables intracellular storage of a sizable pool of presynthesized CX(3)CL1 that protects the chemokine from degradation by metalloproteases at the plasma membrane.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".