Regulation of fibronectin matrix assembly by activated Ras in transformed cells

Fibronectin extracellular matrix plays a critical role in the microenvironm ent of cells. Loss of this matrix frequently accompanies oncogenic transfor mation, allowing changes in cell growth, morphology, and tissue organizatio n. The HT1080 human fibrosarcoma cell lint is deficient in formation of fib ronectin match fibrils but assembly can be induced by the glucocorticoid de x-amethasone, Here we show that fibronectin assembly can also be restored b y stimulation of alpha(5)beta(1) integrin with activating antibody or with Mn2+ suggesting that integrin activity is reduced in these cells. While dex amethasone promoted actin stress fiber formation, actin filaments remained cortical following Mn2+ treatment shelving that the dexamethasone effect is not due solely to cytoskeletal changes. HT1080 cells have one activated al lele of N-ras and PD98059 inhibition of signaling from Ras through ERK incr eased fibronectin matrix accumulation. Conversely, the p38 MAP kinase inhib itor SB203580 blocked induction of matrix and increased ERK phosphorylation , Thus, two MAP kinase pathways contribute to the control of integrin-media ted fibronectin assembly, ERK activity and fibronectin assembly were linked in three different ras-transformed cell Lines but not in SV40- or RSV-tran sformed cells indicating that oncogenic Ras uses a distinct mechanism to do wn-regulate cell-fibronectin interactions.