Transforming growth factor-beta: a growth factor inducing alpha B-crystallin expression in ciliary muscle cells.

Abstract

In a recent study we showed that, in vitro, transforming growth factor-beta 2 (TGF-beta 2) induces alpha B-crystallin expression in cultured trabecular meshwork (TM) cells, but not in cultured fibroblasts. We assumed that alpha B-crystallin can be induced by TGF-beta 2 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 alpha B-crystallin and investigated the effect of TGF-beta on expression of alpha B-crystallin and the corresponding mRNA in these cells. 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-beta 1 or TGF-beta 2. Induction of alpha B-crystallin and the related mRNA was investigated by immunofluorescence and by western and northern blot analysis. An increase in alpha B-crystallin mRNA was observed following treatment with TGF-beta. Actinomycin blocked the induction of alpha B-crystallin by the cytokine TGF-beta. Using western blotting the increase in alpha B-crystallin expression in CM cells was only small. These results confirm our assumption that induction of alpha B-crystallin by the cytokine TGF-beta depends on basal levels of the protein and its mRNA constitutively present within the cells. Comparison of the increase in alpha B-crystallin mRNA and protein expression indicate that post-transcriptional regulation mechanisms are responsible for these findings in CM cells.