Requirement for tyrosine kinase-ERK1/2 signaling in alpha 1 beta 1 integrin-mediated collagen matrix remodeling by rat mesangial cells

Abnormal mesangial extracellular matrix remodeling by mesangial cells (MCs) is the hallmark of progressive glomerulonephritis (GN). We recently showed , using a type I collagen gel contraction assay, that alpha1 beta1 integrin -dependent MC adhesion and migration are necessary cell behaviors for colla gen matrix remodeling. To further determine the mechanism of alpha1 beta1 i ntegrin-mediated collagen remodeling, we studied the signaling pathways of MCs that participate in the regulation of collagen gel contraction. Immunop recipitation and phosphotyrosine detection revealed that gel contraction is associated with the enhanced activity and phosphorylation of ERK1/2 by MCs . The tyrosine kinase inhibitors herbimycin and genistein inhibited collage n gel contraction dose dependently. Furthermore, targeting ERK1/2 activity with a MEK inhibitor, PD98059, and antisense ERK1/2 hindered gel contractio n in a dose-dependent manner. Similar inhibitory effects on gel contraction and ERK1/2 phosphorylation were observed when MC-mediated gel contraction was performed in the presence of function-blocking anti-alpha1 or anti-beta 1 integrin antibodies. However, cell adhesion and migration assays indicate d that PD98059 and antisense ERK1/2 blocked alpha1 beta1 integrin-dependent MC migration, but did not interfere with collagen adhesion, although there was a marked decrease in ERK1/2 phosphorylation and ERK1/2 protein express ion in cell adhesion on type I collagen. None of the above could affect mem brane expression of alpha1/beta1 integrin. These results suggested that ERK 1/2 activation is critical for the alpha1 beta1 integrin-dependent MC migra tion necessary for collagen matrix reorganization. We therefore conclude th at ERK1/2 may serve as a possible target for pharmacological inhibition of pathological collagen matrix formation in GN. (C) 2001 Academic Press.