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 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".