Molecular Characterization of a PU.1 Transcription Complex Formed on the IL-1β Proximal Promoter.
Bibliographic record
Abstract
Abstract The gene coding for the pro-inflammatory cytokine IL-1β is induced at the transcription level in differentiating macrophages and in stress response. Interestingly, PU.1 and C/EBPβ, two transcription factors implicated in IL-1β gene expression are not induced by stress exposure, while c-Jun is strongly induced. Strikingly, this upregulation of c-Jun is required for IL-1β induction, as cells expressing a c-Jun antisense construct fail to respond to stress exposure. We have mapped the induction of IL-1β gene expression to its proximal promoter and show that it is mediated by the transcriptional synergy between C/EBPβ, c-Jun and PU.1 via specific DNA binding sites for C/EBPβ and PU.1 only. To elucidate how PU.1 and C/EBPβ cooperate with c-Jun at the molecular level, we have optimized a DNA binding assay based on IL-1β promoter fragments immobilized on beads to isolate protein complexes from nuclear extracts, which were subsequently eluted and identified by Western blotting. We show that PU.1 or C/EBPβ alone directly bind this promoter fragment via specific sequences while purified recombinant c-Jun fails to do so. However, the presence of either PU.1 or C/EBPβ on the promoter allows for a recruitment of c-Jun to the DNA template, mediated by direct protein-protein interaction. Interestingly, the leucine zipper domain of c-Jun is essential for its interaction with C/EBPβ while dispensable for PU.1 interaction in vitro whereas its basic domain is required for both interactions. Furthermore, we show that PU.1 and C/EBPβ cooperatively bind the IL-1β promoter, resulting in a synergistic recruitment of c-Jun. Finally, we show that the strength of interaction of c-Jun mutants with PU.1 or C/EBPβ determine the strength of transcription output and c-Jun mutants that fail to associate with either PU.1 or C/EBPβ are transcriptionally inactive. In contrast, c-Jun mutants exhibiting increased homodimerization are more active that the wild type protein. Taken together, our data suggest that c-Jun homodimers can be targeted to the IL-1β promoter in the absence of a specific DNA binding element, and conclude that PU.1 and C/EBPβ are specifically tethered to the IL-1β promoter while c-Jun cooperatively binds these proteins and acts as a transcriptional co-activator. We propose a mechanism based on an initial binding of PU.1 and C/EBPβ to the IL-1β promoter followed by a cooperative recruitment of c-Jun, resulting in transcriptional synergy and IL-1β gene expression in stress response.
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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".