The thrombin cleavage domain of osteopontin is important for mediating growth and adhesive properties of human breast cancer cells
Bibliographic record
Abstract
3432 Osteopontin (OPN) is a secreted phosphoprotein that has been associated with malignancy of breast and other cancers. OPN contains several conserved structural domains, including two integrin-binding sites and a thrombin cleavage site located in close proximity to each other. Recent evidence indicates that thrombin, commonly known for its proteolytic role in coagulation, may also play an important role in tumor growth and metastasis. The presence of a thrombin cleavage site in the OPN backbone suggests that the function of OPN may rely, at least in part, on its interaction with thrombin. The purpose of this study was to determine if OPN-mediated malignancy depends on conservation of the thrombin cleavage site within OPN. MDA-MB-468 human breast cancer cells were stably transfected to overexpress wildtype OPN (468-OPN), mutant OPN containing a deleted thrombin cleavage site (468-ΔTC), or a control vector (468-CON). Pooled populations of 468-OPN, 468-ΔTC, and 468-CON cells were compared for functional differences in malignant behavior in vitro, including cell proliferation, plating efficiency (colony formation), and cell adhesion. Proliferation assays demonstrated that there was no significant difference in doubling time between the three cell lines. However, an extended lag phase in the growth of 468-ΔTC cells was observed relative to 468-OPN and 468-CON cells. In plating efficiency assays, overexpression of either wildtype OPN or thrombin-uncleavable OPN resulted in the formation of a significantly greater number of colonies relative to control, but the mean diameter of the colonies formed by 468-ΔTC cells was significantly less than colonies formed by 468-OPN cells. Overexpression of wildtype OPN also resulted in significantly increased cell adhesion to vitronectin, and this adhesion was dependant on conservation of the thrombin cleavage site. Differences in cell growth and adhesion were specific to the interaction between OPN and thrombin, since treatment with the thrombin-specific inhibitor Argatroban caused 468-OPN cells to develop an extended lag phase of growth similar to that shown by 468-ΔTC cells, as well as significantly reducing their adhesion to vitronectin. In contrast, treatment with Argatroban had little effect on the growth or adhesion of 468-ΔTC and 468-CON cells. These novel findings indicate that the thrombin cleavage site in OPN is important for mediating growth and adhesive properties of MDA-MB-468 breast cancer cells in vitro, potentially by increasing accessibility to adjacent integrin-binding sites. Ongoing studies are aimed at determining the involvement of integrins, as well as investigating the role of thrombin in OPN-mediated malignancy in vivo. These studies complement clinical findings in our laboratory that have identified OPN as an important prognostic indicator and potential therapeutic target in breast cancer patients.
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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".