Transforming growth factor-β: a growth factor inducing αB-crystallin expression in ciliary muscle cells

Abstract 

Background: In a recent study we showed that, in vitro, transforming growth factor-β2 (TGF-β2) induces αB-crystallin expression in cultured trabecular meshwork (TM) cells, but not in cultured fibroblasts. We assumed that αB-crystallin can be induced by TGF-β2 only if the cells are already expressing a basal level of the protein. In the present study we therefore treated cultured ciliary muscle (CM) cells constitutively expressing αB-crystallin and investigated the effect of TGF-β on expression of αB-crystallin and the corresponding mRNA in these cells. Material and methods: Monolayer cultures of third-passage CM cells from eyes of five human donors (12–73 years), being confluent for 7 days, were treated with 1.0 ng/ml TGF-β1 or TGF-β2. Induction of αB-crystallin and the related mRNA was investigated by immunofluorescence and by western and northern blot analysis. Results: An increase in αB-crystallin mRNA was observed following treatment with TGF-β. Actinomycin blocked the induction of αB-crystallin by the cytokine TGF-β. Using western blotting the increase in αB-crystallin expression in CM cells was only small. Conclusion: These results confirm our assumption that induction of αB-crystallin by the cytokine TGF-β depends on basal levels of the protein and its mRNA constitutively present within the cells. Comparison of the increase in αB-crystallin mRNA and protein expression indicate that post-transcriptional regulation mechanisms are responsible for these findings in CM cells.