Molecular Cloning of Paired Related Homeobox 2 (Prx2) as a Novel Pituitary Transcription Factor

This study aimed to identify protein(s) that bind(s) to the highly AT-rich sequence of porcine Fshb promoter region -852/-746 (named Fd2) by the Yeast One-Hybrid Cloning System and finally a paired related homeodomain transcription factor, Prx2, known as a key factor for skeletogenesis was cloned. RT-PCR analysis of fetal and postnatal porcine pituitaries demonstrated that Prx2 starts to be expressed at around fetal days 40-50 just before the beginning of Lhb-expression and that the level of Prx2 increases after birth. Immunohistochemical analysis of the prepubertal porcine pituitary revealed that some Prx2-positive cells overlap some Lh beta-positive cells. Transient transfection assay using non-pituitary CHO cells and pituitary tumor-derived L beta T2 cells revealed that Prx2 plays a cell-type dependent role in modulation of the Fshb promoter, showing stimulation in CHO cells and repression in L beta T2 cells via the regions of Fd2 and -596/-239. The binding ability of Prx2 to the regions of Fd2 and -596/-239 was confirmed by electrophoretic mobility shift assay. DNase I footprinting revealed that broad regions of Fd2 were bound by Prx2 and that -596/-239 contained seven Prx2-binding sites. The SELEX method using a random N15-mer oligonucleotide pool demonstrated that Prx2 monomer binds to a TAATT motif, which is present in Fd2 and -596/-239. However, the binding of Prx2 to TAATT with a single molecule and its inverted repeat with two molecules could not induce transcriptional activation, indicating that the Prx2-dependent transcriptional modulation demonstrated in cultured cells is not introduced by Prx2 alone. Thus, this study demonstrated for the first time that Prx2 is expressed in the pituitary gland and at least in a part of gonadotropes in which Prx2 may play a role in repression of the Fshb gene.