Essential but differential role of FOXL2wt and FOXL2C134W in GDF-9 stimulation of follistatin transcription in co-operation with Smad3 in the human granulosa cell line COV434

摘要

The FOXL2^C134W mutation has been identified in virtually all adult granulosa cell tumors (GCTs). Here we show that the exogenous FOXL2 expression is necessary for GDF-9 stimulation of follistatin transcription in the human GCT cell line, COV434 that lacks endogenous FOXL2 expression. Interestingly, in the presence of Smad3 co-expression, FOXL2^C134W negated GDF-9 stimulation of follistatin transcription. However, mutation of the Smad binding element (SBE) located in the intronic enhancer elements in the follistatin gene restored normal FOXL2 activity to FOXL2^C134W, thus the altered activity of FOXL2^C134W is dependent on the ability of Smad3 to directly bind the SBE. Mutation of the FOXL2 binding element (FBE) or the FBE and SBE completely prevented GDF-9 activity, suggesting that the FBE is essential for GDF-9 stimulation in COV434. Overall, our study supports the view that altered interaction of FOXL2^C134W with co-factors may underlie the pathogenesis of this mutation in GCTs.