PI-3-kinase and MAPK regulate mesangial cell proliferation and migration in response to PDGF

Abstract

Proliferation and migration are important biological responses of mesangial cells to injury. Platelet-derived growth factor (PDGF) is a prime candidate to mediate these responses in glomerular disease. PDGF and its receptor (PDGFR) are upregulated in the mesangium during glomerular injury. We have recently shown that PDGF activates phosphatidylinositol 3-kinase (PI-3-kinase) in cultured mesangial cells. The role of this enzyme and other more distal signaling pathways in regulating migration and proliferation of mesangial cells has not yet been addressed. In this study, we used two inhibitors of PI-3-kinase, wortmannin (WMN) and LY-294002, to investigate the role of this enzyme in these processes. Pretreatment of mesangial cells with WMN and LY-294002 dose-dependently inhibited PDGF-induced PI-3-kinase activity assayed in antiphosphotyrosine immunoprecipitates. WMN pretreatment also inhibited the PI-3-kinase activity associated with anti-PDGFRβ immunoprecipitates prepared from mesangial cells treated with PDGF. Pretreatment of the cells with different concentrations of WMN resulted in a dose-dependent inhibition of PDGF-induced DNA synthesis. Both WMN and LY-294002 inhibited PDGF-stimulated migration of mesangial cells in a dose-dependent manner. It has recently been shown that PI-3-kinase physically interacts with Ras protein. Because Ras is an upstream regulator of the kinase cascade leading to the activation of mitogen-activated protein kinase (MAPK), we determined whether activation of PI-3-kinase is necessary for activation of MAPK. Pretreatment of mesangial cells with WMN and LY-294002 significantly inhibited PDGF-induced MAPK activity as measured by immune complex kinase assay of MAPK immunoprecipitates. Furthermore, PD-098059, an inhibitor of MAPK-activating kinase inhibited PDGF-induced MAPK activity and resulted in significant reduction of mesangial cell migration in response to PDGF. These data indicate that MAPK is a downstream target of PI-3-kinase and that both these enzymes are involved in regulating proliferation and migration of mesangial cells.

Activation of mitogen‐activated protein kinase by muscarinic receptors in astroglial cells: Role in DNA synthesis and effect of ethanol

“…7). The PI3K-specific inhibitor LY294002 and genistein, a fairly broad-spectrum tyrosine kinase inhibitor, decreased carbachol-induced MAPK activation, but only at concentrations that exceeded those required specifically to inhibit their respective targets (Choudhury et al, 1997;Akiyama et al, 1987). This suggests that a G ␤␥ -mediated activation of MAPK via PI3K or tyrosine kinase is not a relevant pathway in this cell type.…”

Akt Down-Regulates ERK1/2 Nuclear Localization and Angiotensin II-induced Cell Proliferation through PEA-15

“…PI3K has been shown to stimulate integrin-mediated Raf activation in synergy with Ras (Chaudhary et al, 2000). Cooperative effects between these two signaling cascades have also been demonstrated in the regulation of the platelet-derived growth factor-induced proliferation (Choudhury et al, 1997) or in cell cycle progression and transformation (Sheng et al, 2001a, b). Alternatively, Akt has been shown to phosphorylate Raf-1, leading to the downregulation of the ERK pathway in phorbol 12-myristate 13-acetate-stimulated MCF-7 cells or in differentiated myotubes (Rommel et al, 1999).…”

Inhibition of platelet-derived growth factor signalling induces autophagy in malignant glioma cells

“…These results suggest that the inhibition of Akt signalling might play an important role in the induction of autophagy in malignant glioma cells. Activated signalling molecules further transduce signal transduction pathways by activating downstream signalling molecules such as mitogen-activated protein kinase family members (Yu et al, 1994;Choudhury et al, 1997;Maudsley et al, 2000;Lokker et al, 2002). These signals enter the nucleus and stimulate the expression of a set of immediate-early response genes mediating PDGF-induced cellular processes such as cell cycle, migration, and transformation.…”