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Updated: Aug 10, 2026
Experimental Models for Study of Retinal Pigment Epithelial Physiology and Pathophysiology
Published on: November 7, 2010
TGF-beta receptors are diminished after retinoid exposure in rat liver epithelial cells
T Mercier1, I Gaillard-Sanchez, P Martel
1Laboratoire de Nutrition et Securite Alimentaire, INRA-CRJ, 78352 Jouy-en-Josas Cedex, France.
Abstract:
When rat liver epithelial cells were exposed to retinoic acid or retinol for 24 hr, the levels of transforming growth factor-beta (TGF-beta) receptors were reduced in a dose-dependent way. The decrease appeared after 12 hr of incubation with the retinoids and binding levels remained low until 24 hr after the removal of the molecules. Retinoid treatment induced a fourfold enhancement of transglutaminase (TGase) activity in the cell membranes, and cystamine, an inhibitor of TGase, prevented the decrease of the receptors. Neutralization of TGF-beta by a monoclonal antibody did not suppress the decrease of the binding levels, indicating that decreased TGF-beta binding capacity was not due merely to the internalization of ligand-bound receptors promoted by a stimulation of TCF-beta synthesis. Thus, retinoid treatment resulted in an intense disappearance of the functional receptors from the membranes that seemed to be mediated by increased TGase activity. This phenomenon can represent a strong signal attenuation for TGF-beta following retinoid exposure.
Insights
Retinoid exposure, like retinoic acid, reduces transforming growth factor-beta (TGF-beta) receptors on rat liver cells. Increased transglutaminase (TGase) activity mediates this reduction, impacting TGF-beta signaling.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Transforming growth factor-beta (TGF-beta) is a crucial cytokine regulating cell proliferation, differentiation, and immune responses.
- Retinoids, including retinoic acid and retinol, are vital for cellular processes and are known to influence gene expression and signaling pathways.
Purpose of the Study:
- To investigate the effect of retinoid exposure on the levels and function of TGF-beta receptors in rat liver epithelial cells.
- To elucidate the molecular mechanisms underlying retinoid-induced changes in TGF-beta receptor expression.
Main Methods:
- Rat liver epithelial cells were treated with varying concentrations of retinoic acid or retinol.
- Transforming growth factor-beta (TGF-beta) receptor binding levels were quantified using radioligand assays.
- Transglutaminase (TGase) activity was measured in cell membranes.
- The effect of cystamine (a TGase inhibitor) and a monoclonal antibody against TGF-beta on receptor levels was assessed.
Main Results:
- Retinoid treatment led to a dose-dependent decrease in TGF-beta receptor levels, observable after 12 hours and persisting post-treatment.
- A significant fourfold increase in membrane-bound TGase activity was observed following retinoid exposure.
- Inhibition of TGase by cystamine prevented the retinoid-induced decrease in TGF-beta receptors.
- Neutralization of TGF-beta did not prevent the receptor level reduction, suggesting it's not solely due to ligand-induced internalization.
Conclusions:
- Retinoid administration causes a substantial reduction in functional TGF-beta receptors on the cell surface.
- Increased transglutaminase (TGase) activity appears to be the primary mediator of this receptor downregulation.
- This mechanism represents a significant attenuation of TGF-beta signaling in response to retinoid exposure.
