Objective:It has been found that the expression of Hedgehog signaling molecule Gli1 can inhibit the activity of estrogen signaling pathway.The present study is to observe the effect of estrogen receptor α (ERα) on the transactivation and expression of Gli1 in breast cancer cells,so as to study whether there is a cross talk between the two pathways.Methods: Using luciferase reporter gene transactivation analysis,we cotransfected MCF-7 cells with pGli-BS-luc,pcDNA3.1-Gli1,pRL-CMV,pSG5-ERα or equimolar amounts of pSG5 vector.Then the cells were subjected to Luciferase Assays to analyze the change of Gli1 transactivation.The mRNA and protein expression of Gli1 following ectopic overexpression of ERα was also analyzed by quantitative real-time PCR and Western blotting analysis.Results: Expression of ERα induced the luciferase activity in a dose-dependent manner.ERα at 500 ng/well increased the activity of luciferase by 3.5 folds (P<0.001).The luciferase activity had no obvious changes after estrogen treatment.Overexpression of ERα increased the expression of Gli1 mRNA by 2 folds (P<0.01),and obviously increased the expression of Gli1 protein.Conclusion: Overexpression of ERα in MCF-7 cells can greatly increase the transactivity of Gli1 and increase its expression,which indicates that there is a cross talk between the two transcription factors in breast cancer cells.