Differential expression of the fibronectin isoform containing the ED-B oncofetal domain in normal human fibroblast cell lines originating from different tissues.

Fibronectin (FN) polymorphism is due both to alternative splicing of three sequences (ED-A, ED-B, and IIICS) of the primary transcript and to post-translational modifications. The FN isoform containing the ED-B sequence (B-FN), while having an extremely restricted distribution in normal adult tissues, has a high expression in fetal and tumor tissues. On a panel of non-fetal skin, fetal skin, and fetal lung fibroblast cell lines we have studied, through S1-nuclease protection analysis, the expression of the ED-B containing FN mRNA as well as the expression of the ED-B containing FN isoform through immunoblotting and immunofluorescence techniques, using domain specific monoclonal antibodies. The results show that the expression of B-FN in the different fibroblast cell lines has an extremely great variability depending on the developmental stage of the donor and on the tissue of origin. Moreover, we found that SV-40-transformed fibroblasts present a higher expression of B-FN mRNA with respect to their normal counterparts. An increase in the relative amount of the B-FN isoform in normal human fibroblasts was also obtained by treatment with transforming growth factor-beta.