Down-regulation of fibronectin gene expression by the p53 tumor suppressor protein.

The tumor suppressor p53 protein down-regulates in vitro the expression of several cellular and viral promoters. However, it is not clear whether this down-regulation reflects equivalent modulation of the activity of these promoters in vivo. Here, we propose a suitable system to assess the effect of p53 on gene expression in vivo: the pair of p53 antisense-transfected and parental HeLa cells. The low amount of free wild-type p53 in HeLa cells seems still sufficient for the repression of several promoters that might be derepressed in p53 antisense-transfected HeLa cells. We have used this system for the demonstration both in vivo and in vitro of the repression of the fibronectin (FN) gene promoter by wild-type p53. The protein and mRNA amounts for FN were increased in the p53 antisense-transfected HeLa clones. This was accompanied by the restoration of the FN network in these cells. FN promoter constructs fused to the chloramphenicol acetyltransferase reporter gene were specifically repressed by wild-type p53 in different cell lines. Integrin alpha 5 beta 1 clustering was changed in the sites of focal contacts, most probably representing its relocalization as a consequence of the increased amounts of fibronectin.