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Madhuja Gupta, Everad Tilokee, Judith West-Mays; MRTF-A As A Novel Biomarker Of EMT In Lens Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3931.
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© ARVO (1962-2015); The Authors (2016-present)
Epithelial to mesenchymal transition (EMT) of cells is a key feature of fibrosis and occurs during both anterior subcapsular cataract (ASC) and posterior capsular opacification (PCO) formation. TGFβ is a known inducer of EMT and recent studies have shown in other systems that nuclear localization of the myocardin-related transcription factor-A (MRTF-A) is downstream of TGFβ. In the following study we investigated whether nuclear translocation of MRTF-A is involved in TGFβ-induced EMT of lens epithelial cells.
A human lens epithelial cell line (FHL124) and rat lens explant cultures were used as model systems. Both cell culture systems were treated with TGFβ as well as two different actin binding drugs, Cytochalasin D (CD) and Latranculin B (LatB). These drugs interact with the actin cytoskeleton in the cell and thus affect the intra-cellular movement of MRTF-A. CD facilitates nuclear translocation of MRTF-A even in absence of TGFβ. On the other hand, LatB interrupts nuclear import of MRTF-A despite being co-treated with TGFβ. MRTF-A translocation in the cells was assessed by immunofluorescence and the EMT of cells was determined by examining expression of alpha smooth muscle actin(αSMA).
In both cell culture systems, untreated cells exhibited very little expression of αSMA and MRTF-A was found to reside mostly in the cytosol. However, when stimulated with TGFβ for 48 hours, a much greater number of cells exhibited nuclear expression of MRTF-A and this was accompanied by an increase in expression of αSMA. Furthermore, when the cells were treated with CD alone, increased nuclear expression of MRTF-A was observed along with an induction in expression of αSMA. However, in cells co-treated with LatB and TGFβ, MRTF-A is present mostly in the cytosol and αSMA expression is diminished compared to cells treated with TGFβ alone.
Our results are the first to demonstrate expression of MRTF-A in lens epithelial cells and that TGFβ stimulates the nuclear translocation of MRTF-A in these cells. It is evident from the results that MRTF-A nuclear localization is directly related to αSMA production and EMT in lens epithelial cells. In addition, findings for the actin binding drugs demonstrates that in this system, preventing MRTF-A nuclear translocation can inhibit TGFβ-induced EMT. Therefore, in the future, MRTF-A may be used as a downstream target for preventing ASC and PCO.
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