Rapid Insulin-like Growth Factor-1-induced Changes in Granulosa Cell Thrombospondin-1 Expression In Vitro
Bibliographic record
Abstract
Thrombospondin-1 (TSP-1) is a large extracellular matrix-associated protein that is important for normal follicular development, is rapidly modulated during follicular growth and plays important roles in cellular proliferation and angiogenesis. TSP-1 mRNA is post-transcriptionally regulated, although the underlying mechanisms are largely unknown. Insulin-like growth factor-1 is a potent signalling molecule that participates in folliculogenesis. We hypothesized that IGF-1 modulates TSP-1 expression in granulosa cells, and that such modulation requires rapid turnover of the TSP-1 mRNA and protein. Spontaneously-immortalized rat granulosa cells (SIGC) were cultured in the presence or absence of IGF-1, after which the expression and turnover of TSP-1 mRNA and protein was evaluated by western blot and quantitative PCR. RNA stability reporter constructs were prepared in which wild-type and mutated AU-rich elements from the TSP-1 3'UTR were cloned downstream of the luciferase gene in a mammalian expression vector. These were transfected into SIGC cells in order to characterize mRNA elements that regulate the stability of the TSP-1 mRNA. TSP-1 expression decreased rapidly at the mRNA and protein levels in IGF-1 treated cultures. Following 12 h of IGF-I treatment, TSP-1 protein decreased by 25% and was 73% lower than in untreated cultures. The half-life of endogenous TSP-1 mRNA in SIGC was 2.0 h. This was not changed in the presence of IGF-1, however, transcription of new TSP-1 mRNA was inhibited. Reporter mRNAs with mutated AU-rich elements demonstrated a longer half-life than mRNAs in which the wild type AU-rich elements were present. These studies reveal that IGF-1 rapidly inhibits TSP-1 expression at the protein and mRNA levels in cultured granulosa cells through apparent inhibition of TSP-1 transcription. The decrease depends on an intrinsically short half-life of TSP-1 mRNA and protein. The short mRNA half life is due, at least in part, to AU-rich elements in the 3'UTR of the TSP-1 mRNA.
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How this classification was reachedexpand
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 | 0.000 | 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) | 0.000 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".