Activation of extracellular signal-regulated protein kinase1,2 results in down-regulation of decorin expression in fibroblasts.

Decorin is a small leucine-rich extracellular matrix proteoglycan, the expression of which is down-regulated in proliferating and malignantly transformed cells. In the present study we show that the expression of decorin in fibroblasts is suppressed by epidermal growth factor (EGF) and PMA, and that the effect of both is potently inhibited by blocking the extracellular signal-regulated protein kinase (ERK)1,2 signalling pathway (Raf/MEK1,2/ERK1,2) with the specific MAPK/ERK kinase (MEK)1,2 inhibitor, PD98059. In addition, specific activation of ERK1,2 by adenovirus-mediated expression of constitutively active MEK1 in dermal fibroblasts results in marked reduction in decorin mRNA abundance and production. Co-transfection of NIH-3T3 fibroblasts with human decorin promoter/chloramphenicol acetyltransferase (CAT) construct (pDEC--879/CAT) in combination with the expression vectors for constitutively active Raf-1 and MEK1 markedly suppressed decorin promoter activity. Co-transfections of human decorin promoter 5'-deletion constructs with constitutively active MEK1 expression vector identified the region -278 to -188 as essential for ERK1,2 mediated down-regulation of decorin promoter activity. These results show that activation of the ERK1,2 signalling pathway by a mitogenic growth factor, a tumour promoter or transformation suppresses decorin gene expression in fibroblasts, which in turn may promote proliferation and migration of normal and malignant cells.