Identification of Domains Participating in the Substrate Specificity and Subcellular Localization of the Multidrug Resistance Proteins MRP1 and MRP2
Bibliographic record
Abstract
The human multidrug resistance protein MRP1 and its homolog, MRP2, are both thought to be involved in cancer drug resistance and the transport of a wide variety of organic anions, including the cysteinyl leukotriene C4 (LTC4) (Km = 0.1 and 1 microm). To determine which domain of these proteins is associated with substrate specificity and subcellular localization, we constructed various chimeric MRP1/MRP2 molecules and expressed them in polarized mammalian LLC-PK1 cells. We examined the kinetic properties of each chimeric protein by measuring LTC4 and methotrexate transport in inside-out membrane vesicles, sensitivity to an anticancer agent, etoposide, and subcellular localization by indirect immunofluorescence methods. The following results were determined in these studies: (i) when the NH2-proximal 108 amino acids of MRP2, including transmembrane (TM) helices 1-3, were exchanged with the corresponding region of MRP1, Km(LTC4) values of the chimera decreased approximately 4-fold and Km(methotrexate) values increased approximately 5-fold relative to those of wild-type MRP2 and MRP1, respectively, whereas resistance to etoposide increased approximately 3-fold; (ii) when the NH2-proximal region up to TM9 of MRP2 was exchanged with the corresponding region of MRP1, a further increase in etoposide resistance was observed, and subcellular localization moved from the apical to the lateral membrane; (iii) when two-thirds of MRP2 at the NH2 terminus were exchanged with the corresponding MRP1 region, the chimeric protein transported LTC4 with an efficiency comparable with that achieved by the wild-type MRP1; and (iv) exchange of the COOH-terminal 51 amino acids between MRP1 and MRP2 did not affect the localization of either of the proteins. These results provide a strong framework for further studies aimed at determining the precise domains of MRP1 and MRP2 with affinity for LTC4 and anticancer agents.
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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 | 0.000 |
| 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".