Ligands for several nuclear receptors inhibit expression of stromelysin in human retinal pigmented epithelial cells

Purpose. We have previously demonstrated that all-trans retinoic acid (RA) inhibits the proliferation of retinal pigmented epithelial (RPE) cells, and that the inhibitory effect of RA is enhanced when it is used in combination with ligands for other nuclear receptors including dexamethasone (Dex), tri-iodothyronine (T₃), or vitamin D₃ (D₃). In this study, we sought to determine if RA, Dex, T₃ and D₃ alter gene expression in RPE cells; for our target gene we selected stromelysin, a metalloproteinase. Methods. Human RPE cells at confluence were incubated for 14 h with vehicle alone, 12-O-tetradecanoylphorbol 13-acetate (TPA; 162 nM), or RA, T₃, or D₃ (1 μM) in the presence or absence of TPA. Total RNA was isolated and unique oligonucleotide pairs for human stromelysin were used to measure stromelysin mRNA by RT-PCR. Primers for ribosomal RNA were used in all reactions as an internal control. Results. There was low level constitutive expression of stromelysin in cultured RPE that was markedly stimulated by incubation with TPA and markedly decreased by incubation with RA. Co-incubation with TPA and RA, Dex, T₃, or D₃ blocked the induction by TPA. Conclusions. RA, Dex, T₃, and D₃ are all strong inhibitors of stromelysin gene expression in RPE cells. Since TPA stimulates transcription through the AP-1 site, the nuclear receptors may all act through antagonism at AP-1 and this may result in their inhibition of RPE proliferation. Inhibition of stromelysin expression in RPE cells by RA, Dex, T₃, and D₃ may have implications for therapy of choroidal neovascularization in which metalloproteinases have been implicated.