ACTIVIN EXPRESSION BY CULTURED HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS

Purpose. To determine whether human retinal pigment epithelial (hRPE) cells produce activin, a growth factor in the transforming growth fact or beta family, and to characterize growth regulatory effects of activ in on retinal pigment epithelium. Methods. mRNA expression was examine d using polymerase chain reaction with primers specific for the beta A and beta B chains of activin and by slot blot analysis with a probe s pecific for the beta A chain. Protein localization was determined immu nocytochemically using antibodies specific for the beta A chain of act ivin and intact activin A. The effect of activin A on DNA synthesis wa s studied by measuring (H-3) thymidine incorporation after cells were exposed to recombinant human activin A (rhA). Growth regulatory effect s of rhA on hRPE cells were examined with cell growth assays. Results. beta A mRNA was expressed constitutively in 8/8 cell lines tested. be ta B mRNA was not expressed in any of the six cell lines tested but wa s expressed in human ovarian granulosa cell controls. Positive immunos taining was observed for both the beta A chain and intact activin A. ( H-3) thymidine incorporation was inhibited 44% (P < 0.025), 45% (P < 0 .025), and 44% (P < 0.015) when RPE cells were exposed to 100 ng/ml rh A and grown in serum-free medium, medium with 0.5% serum, and 1% serum , respectively. Cell growth was inhibited 33.2% (P = 0.0001) after RPE cells were exposed to 100 ng/ml rhA for 8 days. Conclusions. These re sults suggest that activin A can act as an autocrine-paracrine growth regulator in RPE cells and may help control cellular growth in ocular development and proliferative eye disease.