Expression of the alpha(5) integrin subunit gene promoter is positively regulated by the extracellular matrix component fibronectin through the transcription factor Sp1 in corneal epithelial cells in vitro
K. Larouche et al., Expression of the alpha(5) integrin subunit gene promoter is positively regulated by the extracellular matrix component fibronectin through the transcription factor Sp1 in corneal epithelial cells in vitro, J BIOL CHEM, 275(50), 2000, pp. 39182-39192
The accumulation of fibronectin (FN) in response to corneal epithelium inju
ry has been postulated to turn on expression of the FN-binding integrin alp
ha (5)beta (1). In this work, we determined whether the activity directed b
y the ct, gene promoter can be modulated by FN in rabbit corneal epithelial
cells (RCEC). The activity driven by chloramphenicol acetyltransferase/alp
ha (5) promoter-bearing plasmids was drastically increased when transfected
into RCEC grown on FN-coated culture dishes. The promoter sequence mediati
ng FN responsiveness was shown to bear a perfect inverted repeat that we de
signated the fibronectin-responsive element (FRE). Analyses in electrophore
tic mobility shift assays provided evidence that Spl is the predominant tra
nscription factor binding the FRE. Its DNA binding affinity was found to be
increased when RCEC are grown on FN-coated dishes. The addition of the MER
kinase inhibitor PD98059 abolished FN responsiveness suggesting that alter
ation in the state of phosphorylation of Spl likely accounts for its increa
sed binding to the a, FRE. The FRE also proved sufficient to confer FN resp
onsiveness to an otherwise unresponsive heterologous promoter. However, sit
e-directed mutagenesis indicated that only the 3 ' half-site of the FRE was
required to direct FN responsiveness. Collectively, binding of FN to its a
lpha (5)beta (1) integrin activates a signal transduction pathway that resu
lts in the transcriptional activation of the alpha (5) gene likely through
altering the phosphorylation state of Sp1.