title: Modulation of basic fibroblast growth factor effect by retinoic acid in cultured retinal pigment epithelium.
abstract: OBJECTIVE
  We investigated the effect of retinoic acid (RA) on basic fibroblast growth factor (bFGF)-stimulated proliferation of cultured human retinal pigment epithelial (hRPE) cells and of 125I-bFGF-binding to the bFGF plasma membrane receptors of hRPE.
  
  
  METHODS
  Proliferation of hRPE cells in the presence of increasing concentrations of bFGF and bFGF + RA was measured by 3H-thymidine incorporation into hRPE cells. To characterize bFGF receptors, hRPE cells were incubated at 4 degrees C with 125I-bFGF in the presence or absence of heparin.
  
  
  RESULTS
  Basic-FGF stimulated 3H-thymidine incorporation into hRPE cells in a dose-dependent manner. RA inhibited bFGF-stimulated 3H-thymidine incorporation in the presence or absence of heparin. Increasing concentrations of unlabeled bFGF decreased the binding of 125I-bFGF to hRPE cells. Scatchared analysis indicated the presence of high and low affinity binding sites for bFGF with an apparent affinity Kd of 50 pM and 330 pM, respectively, and a binding capacity (Bmax) of 1.25 X 10(5) and 3.38 X 10(5) binding sites per cell. Inhibition of 125I-bFGF binding was 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 125I-bFGF to hRPE cells. Scatchard analysis demonstrated that, in the presence of heparin, there 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 significant change in affinity constants.
  
  
  CONCLUSIONS
  These results suggest that RA inhibits bFGF cell proliferation in hRPE cells by decreasing the bFGF receptor number.
authors.affiliation: Department of Ophthalmology, W. K. Kellogg Eye Center, University of Michigan, Ann Arbor 48105, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kusaka
authors.forename: P C
authors.initials: PC
authors.lastname: Kothary
authors.forename: M A
authors.initials: MA
authors.lastname: Del Monte
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004261:DNA Replication / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism* / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism*; D017468:Receptors, Fibroblast Growth Factor / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D017468:Receptors, Fibroblast Growth Factor; D016222:Fibroblast Growth Factor 2; D014212:Tretinoin; D006493:Heparin; D013936:Thymidine