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Regulation of the redox-mediated platelet-derived growth factor (PDGF) mitogenic function in human lens epithelial cells
Abstract
Platelet-derived growth factor (PDGF), which governs multiple physiological functions in human lens epithelial cells (HLE), has been identified to be involved in reactive oxygen species (ROS)-mediated cell signaling. We found that PDGF activates the cytosolic phospholipase A2 &agr; (cPLA 2&agr;) and the release of free arachidonic acid (AA) from phospholipids of the membrane, which triggers ROS production and the downstream activation of MAPK signaling, followed by cell proliferation. The overexpression of cPLA 2&agr; S228A, a dominant negative form of cPLA2&agr;, has negative effects on ROS production and the activation of ERK and JNK signaling. Experiments based on HLE B3 cells treated with various inhibitors showed that ROS generation induced by AA depends on the activation of PKC, ERK, and lipoxygenase. We concluded that AA plays a positive feedback role in PDGF-induced mitogenic cellular response by enhancing the initial mitogenic signal via activating NADPH oxidase (NOX). We further identified the existence of NOX2 enzymatic complex, which contains gp91phox, p22phox, p47phox, p67phox, p40phox, and Rac, in HLE B3 cells. In p22phox knockdown cells, we found that the levels of PDGF-induced ROS generation and cell proliferation were decreased, whereas the cells with overexpressed p22phox have increased ROS level and elevated cell proliferation. The results of Western blots showed that the expression level of p22phox has positive effects in ERK, JNK, and Akt activation, but not in p38. Interestingly, the increased or decreased ROS levels also regulated the activation of PDGF receptor (PDGFR) via affecting the activity of low molecular weight protein tyrosine phosphatase (LMW-PTP). The role of calcium was also investigated in our studies. The treatment of calcium agonist, ionomycin, induced ROS generation in HLE B3 cells in the absence of PDGF, p22phox, and functional cPLA2&agr;. We then confirmed the expression of NOX5, a Ca2+-dependent and subunits-independent NOX member, in the HLE cells, which may be responsible for such phenomenon. Taken together, our studies suggest the fundamental regulatory model of PDGF signaling in HLE cells. The PDGF-induced mitogenic signals are mediated by PDGFR and can be enhanced by the activation of NOX2 complex and ROS production in an AA- and calcium-dependent fashion.
Subject Area
Molecular biology|Cellular biology|Ophthalmology
Recommended Citation
Wang, Yin, "Regulation of the redox-mediated platelet-derived growth factor (PDGF) mitogenic function in human lens epithelial cells" (2008). ETD collection for University of Nebraska-Lincoln. AAI3331460.
https://digitalcommons.unl.edu/dissertations/AAI3331460