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

Background: In a recent study we showed that, in vitro, transforming growth factor-beta2 (TGF-beta2) induces alphaB-crystallin expression in cultured trabecular meshwork (TM) cells, but not in cultured fibroblasts. We assumed that alphaB-crystallin can be induced by TGF-beta2 only if the cells are a lready expressing a basal level of the protein. In the present study we the refore treated cultured ciliary muscle (CM) cells constitutively expressing alphaB-crystallin and investigated the effect of TGF-beta on expression of alphaB-crystallin and the corresponding mRNA in these cells. Material and Methods: Monolayer cultures of third-passage CM cells from eyes of five hum an donors (12-73 years), being confluent for 7 days, were treated with 1.0 ng/ml TGF-beta1 or TGF-beta2. Induction of alphaB-crystallin and the relate d mRNA was investigated by immunofluorescence and by western and northern b lot analysis. Results: An increase in alphaB-crystallin mRNA was observed f ollowing treatment with TGF-beta. Actinomycin blocked the induction of alph aB-crystallin by the cytokine TGF-beta. Using western blotting the increase in alphaB-crystallin expression in CM cells was only small. Conclusion: Th ese results confirm our assumption that induction of alphaB-crystallin by t he cytokine TGF-beta depends on basal levels of the protein and its mRNA co nstitutively present within the cells. Comparison of the increase in alphaB -crystallin mRNA and protein expression indicate that post-transcriptional regulation mechanisms are responsible for these findings in CM cells.