DOWN-REGULATION OF FIBRONECTIN GENE-EXPRESSION BY THE P53 TUMOR-SUPPRESSOR PROTEIN

The tumor suppressor p53 protein down-regulates in vitro the expressio n of several cellular and viral promoters. However, it is not clear wh ether this downregulation reflects equivalent modulation of the activi ty of these promoters in vivo. Here, we propose a suitable system to a ssess the effect of p53 on gene expression in vivo: the pair of p53 an tisense-transfected and parental HeLa cells. The low amount of free wi ld-type p53 in HeLa cells seems still sufficient for the repression of several promoters that might be derepressed in p53 antisense-transfec ted HeLa cells. We have used this system for the demonstration both in vivo and in vitro of the repression of the fibronectin (FN) gene prom oter by wild-type p53. The protein and mRNA amounts for FN were increa sed in the p53 antisense-transfected HeLa clones. This was accompanied by the restoration of the FN network in these cells. FN promoter cons tructs fused to the chloramphenicol acetyltransferase reporter gene we re specifically repressed by wild-type p53 in different cell lines. In tegrin alpha 5 beta 1 clustering was changed in the sites of focal con tacts, most probably representing its relocalization as a consequence of the increased amounts of fibronectin.