Characterizing New Negative Regulators of Tubular GEF-H1 Signaling: Possible Role in Kidney Fibrosis
Bibliographic record
Abstract
Background: Kidney fibrosis is attributed to chronic injury, inflammation and maladaptive repair caused by kidney diseases of various etiologies. Tubular RhoA proteins, activated by cytokines, regulate release of fibrogenic mediators, including Connective Tissue Growth Factor (CTGF/CCN2). These in turn stimulate mesenchymal cells to produce extracellular matrix proteins. This epithelial-mesenchymal crosstalk is crucial for fibrogenesis. The guanine nucleotide exchange factor GEF-H1 (ArhGEF2), activated and upregulated by inflammatory and pro-fibrotic input, is an activator of tubular fibrogenic RhoA signaling. The dynamic activation-inactivation cycle of GEF-H1, and its fibrosis-related dysregulation however remain poorly understood. This study aimed at identifying new druggable regulators of fibrogenic GEF-H1/RhoA signaling and tubular cytokine production. Methods: LLC-PK1 and hTERT-immortalized human renal proximal tubule cells were used. Proteins coimmunoprecipitating with GEF-H1 were identified using mass spectrometry and verified by western blotting. Expression of key proteins were altered by siRNA-mediated silencing or overexpression. RhoA and GEF-H1 activity were assessed by affinity precipitation assays. Fibrosis-related genes were measured using RT2 Profiler™ PCR Array (Qiagen). Protein and mRNA expression changes were explored in a mouse kidney fibrosis model. Results: GEF-H1 associated with subunits of protein phosphatase 6 (PP6) and with Myotonic Dystrophy Kinase-related Cdc42-binding kinase (MRCK)α. Silencing of either the PP6 catalytic domain (PP6C) or MRCKα stimulated GEF-H1 activity and promoted GEF-H1-dependent RhoA activation. We identified several genes upregulated by depletion of PP6C or MRCKα. Notably, depletion of PP6C or MRCKα activated the RhoA effector Myocardin-related Transcription Factor (MRTF), and elevated MRTF-dependent genes, including CTGF/CCN2 and α-smooth muscle actin. Finally, expression of PP6C was decreased in a mouse kidney fibrosis model and in tubular cells stimulated by TGFβ1. Conclusion: We identified PP6 and MRCKα as new suppressors of GEF-H1/RhoA signaling and tubular fibrotic changes. Cytokine-induced downregulation of these regulators may contribute to epithelial-mesenchymal crosstalk and could represent new drug targets for kidney fibrosis. Funding: Government Support – Non-U.S.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.001 | 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 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".