GnRH-Regulated Expression of Jun and JUN Target Genes in Gonadotropes Requires a Functional Interaction between TCF/LEF Family Members and β-Catenin

Abstract

AbstractGnRH regulates gonadotrope function through a complex transcriptional network that includes three members of the immediate early gene family: Egr1, Jun, and Atf3. These DNA-binding proteins act alone or in pairs to confer hormonal responsiveness to Cga, Lhb, Fshb, and Gnrhr. Herein we suggest that the transcriptional response of Jun requires a functional interaction between the T-cell factor (TCF)/lymphoid enhancer factor (LEF) family of DNA-binding proteins and β-catenin (officially CTNNB1), a coactivator of TCF/LEF. Supporting data include demonstration that GnRH increases activity of TOPflash, a TCF/LEF-dependent luciferase reporter, in LβT2 cells, a gonadotrope-derived cell line. Additional cotransfection experiments indicate that a dominant-negative form of TCF7L2 (TCFDN) that binds DNA, but not β-catenin, blocks GnRH induction of TOPflash. Overexpression of AXIN, an inhibitor of β-catenin, also reduces GnRH stimulation of TOPflash. Transduction of LβT2 cells with TCFDN adenoviruses diminishes GnRH stimulation of Jun mRNA without altering expression of Egr1 and Atf3, two other immediate early genes that confer GnRH responsiveness. Reduction of β-catenin in LβT2 cells, through stable expression of short hairpin RNA, also selectively compromises GnRH regulation of Jun expression and levels of JUN protein. Finally, overexpression of TCFDN attenuates GnRH regulation of Cga promoter activity, a known downstream target of JUN. Together, these results indicate that GnRH regulation of Jun transcription requires a functional interaction between TCF/LEF and β-catenin and that alteration of either impacts expression of JUN downstream targets such as Cga.