Tyrosine Phosphorylation of Runx1 In Megakaryocytes by Src Family Kinases
Bibliographic record
Abstract
Abstract Abstract 742 Runx1 and its cofactor, CBF-beta, are the most frequent targets of chromosomal translocations in human leukemias. Point mutations in Runx-1 also occur in some cases of myelodysplastic syndrome and undifferentiated leukemia. During normal hematopoiesis, Runx1 is required for the ontogeny of all definitive hematopoietic stem cells and for the proper maturation of megakaryocytes (Mks) and lymphocytes. Despite these critical roles, the regulation of Runx1 activity via cell signaling pathways remains incompletely understood. Here, we report that Runx-1 is tyrosine phosphorylated in Mks. This occurs on multiple residues and is mediated by src-family tyrosine kinases (SFKs). Loss of Runx1 tyrosine phosphorylation correlates with phorbol ester induced differentiation of L8057 megakaryoblastic cells, suggesting a negative regulatory function. Consistent with this model, retroviral expression of a tyrosine non-phosphorylatable mutant Runx1 molecule increases primary murine fetal liver Mk maturation and Runx1 target gene expression to a greater extent than wild type Runx1. Moreover, treatment of wild type primary Mks with SFK inhibitors markedly enhances Mk maturation, as previously reported (Lannutti BJ, et al 2005 Blood;105:3875-3878). Treatment of L8057 cells with the pan-tyrosine phosphatase inhibitor Na3VO4, significantly increases Runx1 tyrosine phosphorylation levels, suggesting that tyrosine phosphorylation of Runx1 is dynamically regulated under steady-state conditions. Using a proteomic approach, we found that Runx1 physically interacts with the non-receptor tyrosine phosphatase SHP-2 (Ptpn11). We validated this interaction and showed that it occurs via direct interactions involving the Runx1 runt domain. ShRNA mediated knock down of SHP-2 in L8057 cells increases Runx1 tyrosine phosphorylation levels. Conditional knockout of SHP-2 in Mks using SHP-2fl/fl, PF4-Cre mice leads to reduced peripheral blood platelet counts and delayed platelet recovery following transient anti-GPIb antibody induced immune thrombocytopenia. Lastly, we show that treatment of TPA-induced L8057 cells with Na3VO4 markedly diminishes binding between Runx1 and the key Mk transcription factor GATA-1. Taken together, our data suggest that tyrosine phosphorylation of Runx1 via SFKs inhibits Runx1 function. Dephosphorylation, at least in part via SHP-2, relieves this inhibition and promotes Mk maturation. These effects are likely mediated through altered protein-protein interactions. Disclosures: No relevant conflicts of interest to declare.
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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) | 0.002 | 0.001 |
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".