MODULATION OF BASIC FIBROBLAST GROWTH-FACTOR EFFECT BY RETINOIC ACID IN CULTURED RETINAL-PIGMENT EPITHELIUM

Purpose. We investigated the effect of retinoic acid (RA) on basic fib roblast growth factor (bFGF)-stimulated proliferation of cultured huma n retinal pigment epithelial (hRPE) cells and of I-125-bFGF-binding, t o the bFGF plasma membrane receptors of hRPE. Methods. Proliferation o f hRPE cells in the presence of increasing concentrations of bFGF and bFGF + RA was measured by H-3-thymidine incorporation into hRPE cells. To characterize bFGF receptors, hRPE cells were incubated at 4 degree s C with I-125- bFGF in the presence or absence of heparin. Results. B asic-FGF stimulated H-3-thymidine incorporation into hRPE cells in a d ose-dependent manner. RA inhibited bFGF stimulated H-3-thymidine incor poration in the presence or absence of heparin. Increasing concentrati ons of unlabeled bFGF decreased the binding of I-125-bFGF to hRPE cell s. Scatchard analysis indicated the presence of high and low affinity binding sites for bFGF with an apparent affinity Kd Of 50 pM and 330 p M, respectively, and a binding capacity (B-max) of 1.25 x 10(5) and 3. 38 x 10(5) binding sites per cell. Inhibition of I-125-bFGF binding wa s also possible by the carboxyl-terminal region peptide fragment bFGF- (106-120)-NH2, but not amino-terminal region peptide fragment bFGF-(1- 24)-NH2. The addition of heparin to the medium during binding studies did not prevent RA from inhibiting binding of I-125-bFGF to hRPE cells . Scatchard analysis demonstrated that, in the presence of heparin, th ere is a decrease in the number of high affinity binding sites (from 1 .12 +/- 0.11 X 10(5) to 0.7 +/- 0.03 X 10(5) binding sites per cell, a reduction of 36.7 +/- 0.04%, n = 3, p < 0.05). There was no significa nt change in affinity constants. Conclusions. These results suggest th at RA inhibits bFGF cell proliferation in hRPE cells by decreasing the bFGF receptor number.