Induction of fibronectin gene transcription and mRNA is a primary response to growth-factor stimulation of AKR-2B cells.

Abstract

A cDNA library, prepared from poly(A)+ RNA isolated from quiescent AKR-2B cells 4 hr after stimulation with epidermal growth factor in the presence of cycloheximide, was screened to identify RNA transcripts whose abundance is specifically increased as a primary response to growth stimulation. Approximately 40% of the inducible clones detected by this procedure corresponded to either cytoskeletal 13-or y-actin genes. One nonactin clone, designated c99, was found to be derived from an 8.5-kilobase RNA whose abundance began to increase as early as 30 min after stimulation. DNA sequencing established the identity of this RNA as fibronectin. Several additional mitogens were then tested and found to efficiently induce fibronectin mRNA. These included fetal calf serum, platelet-derived growth factor, and transforming growth factor type P. For at least one inducer, fetal calf serum, the increase in mRNA was preceded by an increase in fibronectin gene transcription. This increase was rapid, reaching maximal levels within 10 min, and was accompanied by near-coordinate increases in both c-fos and 13-actin transcription. These results indicate that fibronectin is a member of a class of "early-response" genes, typified by c-fos and including j3-actin, whose rapid expression may be important in mediating cellular responses to peptide growth factors.Peptide growth factors govern a wide range of cellular activity including embryonic development and differentiation, maintenance of cell-type homeostasis, and wound healing. Genetic and biochemical evidence indicates that cellular responses to growth factors are mediated, in part, through the regulation of specific gene expression. Thus, one approach to understanding how growth factors influence cell behavior is to clone and identify responsive genes. Estimates derived from such endeavors are inexact (1) but suggest that growth factors exert their influence through the action of perhaps 50-100 genes.In studies of cell growth control, particular attention has been focused on genes expressed soon after growth-factor stimulation of quiescent cells in culture. Such genes presumably encode proteins important to growth stimulation and have been shown to include the c-fos and c-myc protooncogenes (2, 3). Interestingly, enhanced expression of the cytoskeletal actin genes is also a prominent and rapid response to mitogenic stimuli in several cell types (4-7). This contrasts with the traditional view of the cytoskeletal actins as passive structural proteins but is broadly consistent with other data suggesting an important role for actin microfilaments in mediating cellular responses to growth factors (8) and in neoplastic transformation (9).Although the exact role of actin in cell growth control is not clear, the degree of anchorage of cells to the extracellular matrix has long been known to influence both cell division and cell differentiation (reviewed in ref. 10). Among the major mediators of cell adhesion are transmembrane glycoproteins that link actin microfilaments on the cytop...

Regulation of the expression of a secreted acidic protein rich in cysteine (SPARC) in human fibroblasts by transforming growth factor β

“…Interestingly, celltype-specific control of fibronectin expression may be mediated by changes in transcription rates and in mRNA stability, since cell lines transformed in vitro display reduced tran- [16,17,19,201. Nevertheless, TGF-fi has been directly demonstrated to regulate fibronectin transcription and mRNA stability in the fibrosarcoma cell line HT 1080 [15].…”

Transcription factors control invasion: AP-1 the first among equals

“…These immediate responses include rapid and dramatic changes in cell adhesion, actin cytoskeleton, cell polarity and membrane organization, often regulated by the Rac-Rho pathway (Ridley and Hall, 1992). Long-term responses include the activation of transcription factors that regulate prolonged changes in gene expression (Blatti et al, 1988;Lanahan et al, 1992). Under normal circumstances, when the initiating signal is withdrawn, or the migrating cell reaches its destination, the invasive response attenuates and migratory fibroblasts can differentiate into stationary myofibroblasts that perform discrete wound healing functions (Grinnell, 1994).…”

A cell cycle and mutational analysis of anchorage-independent growth: cell adhesion and TGF-beta 1 control G1/S transit specifically

“…3); these cells showed no increase in number (not shown). Note that NIH-3T3 and Balb/c 3T3 cells have TGF-/31 receptors as determined by ligand binding (Massagu6 et al, 1990;Segarini, 1990) and respond to 100 pM TGF-/31 as evidenced by stimulation of fibronectin or a5B1 integrin levels (Ignotz and Massagut, 1986;Blatti et al, 1988;and Dalton and Assoian, unpublished data). Moreover, the lack of colony formation in TGF-/~l-treated NIH-3T3 cells and Balb/c 3T3 cells is not likely due to insufficient mitogenic stimulation because the concentrations of mitogens (10% FCS, 1 nM EGF, and 10 #g/ml insulin) that were present in the cultures were highly growth stimulatory for the cells in monolayer.…”