Coexpression of FGF-5 and bFGF by the retinal pigment epithelium in vitro.

Members of the fibroblast growth factor (FGF) gene family have been proposed to play critical roles in the biology of the outer retina. In this study, in vitro cultures of human retinal pigment epithelial (RPE) cells were surveyed for the expression of FGF gene family members. Northern analysis provided evidence for the expression of the previously reported 7.0 and 3.7 kb basic FGF (bFGF) transcripts and for the 4.0 and 2.1 kb FGF-5 transcripts. Western analysis demonstrated the presence of three bFGF proteins ranging in size from 18 to 26 kDa and three FGF-5 proteins of molecular weights 28.5, 34, and 36 kDa. We were particularly interested in cellular mechanisms which might regulate the steady-state mRNA levels of these genes. It was determined that bFGF message levels decreased with increasing culture density, increased upon serum stimulation and when placed in contact with matrix components found in the extracellular matrix of RPE cells in vivo. In a similar fashion, the steady state mRNA levels for FGF-5 decreased with increasing culture density, increased upon serum stimulation, but appeared to be unaffected by matrix contact.