Parathyroid Hormone-related Protein Promotes Quiescence and Survival of Serum-deprived Chondrocytes by Inhibiting rRNA Synthesis
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Bibliographic record
Abstract
Parathyroid hormone-related protein (PTHrP) was initially recognized for its ability to promote parathyroid hormone-like bioactivity in kidney, bone, and squamous epithelial cells. PTHrP is a multifunctional protein in which bioactivity is mediated by two distinct pathways. Its classic parathyroid hormone-like activity results from binding of its amino terminus to cell surface PTH1R and activation of signal transduction pathways. Another less well recognized pathway involves translocation of PTHrP to the nucleus via a mid-region bipartite nuclear targeting sequence (NTS), similar in structure and function to those found in retroviral regulatory proteins. PTHrP was identified in the nucleus of several different cell types in vivo and in vitro, where it has been implicated in cell cycle progression, cellular differentiation, and apoptosis. In previous work we showed that nuclear translocation of PTHrP enhanced the survival of serum-deprived chondrogenic cells, associated with RNA, and localized to a region of the nucleus rich in complexes of newly transcribed ribosomal RNA and protein. In this work we have used two chondrogenic cell lines, CFK2 (PTH1R+) and 27m21 (PTH1R-) to further explore mechanisms whereby PTHrP rescues immature chondrocytes from apoptosis. Endogenous PTHrP and exogenous PTHrP NTS peptide protected serum-deprived cells from apoptosis, in the presence and absence of PTH1R. The survival of cells expressing PTHrP and those treated with PTHrP NTS peptide was associated with a rapid shift into G(o)/G1 accompanied by a significant down-regulation of rRNA synthesis and a decrease in the number of actively translating polyribosome complexes. Together with our previous observations, this work predicts a role for PTHrP in modulating ribosome biogenesis and preventing chondrogenic cells from progressing through the cell cycle in an unfavorable environment.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| 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) | 0.000 | 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 it