A New Role for Wilms Tumor Protein 1: Differential Activities of plus KTS and -KTS Variants to Regulate LHβ Transcription

Luteinizing hormone (LH) is synthesized and secreted throughout the reproductive cycle from gonadotrope cells in the anterior pituitary, and is required for steroidogenesis and ovulation. LH contains an a-subunit common with FSH, and a unique LH beta subunit that defines biological activity. Basal LH beta transcription is low and stimulated by hypothalamic GnRH, which induces synthesis of early growth response protein-1 (Egr1), and stimulates binding of transcription factors Egr1 and steroidogenic factor-1 (SF1) on the promoter. WT1 (Wilms tumor protein1) is a zinc finger transcription factor with an essential role in urogenital system development, and which regulates several reproductive genes via interactions with SF1 or binding to GC-rich elements such as Egr1 binding sites. We investigated a potential role for WT1 in LH beta transcription in clonal mouse gonadotrope L beta T2 cells. WT1 was present in L beta T2 and mouse pituitary cells, and protein bound to the endogenous LH beta promoter. Interestingly, mRNAs for WT1(+KTS), which contains a three amino-acid insertion between the 3rd and 4th zinc fingers, and the WT1 (-KTS) variant were both expressed at significant levels. WT1 mRNAs and protein were decreased approximately 50% by GnRH treatment, under conditions where Egr1 mRNA and protein, and LH beta transcription, were stimulated. Decreasing expression of mRNA for WT1 (-KTS) decreased stimulation of LH beta and Egr1 by GnRH, whereas decreasing both WT1 (-KTS) and (+KTS) increased endogenous LH beta transcription, and prevented LH beta but not Egr1 stimulation by GnRH, suggesting differing biological activities for the WT1 isoforms. Overexpression of WT1 showed that WT1(-KTS) enhanced LH beta promoter GnRH stimulation 2-to-3-fold and required the 3' Egr1 site, but WT1(+KTS) repressed both basal and GnRH-stimulated LH beta promoter activity by approximately 70%. Our data suggest that WT1 can modulate LH beta transcription, with differential roles for the two WT1 variants; WT1 (-KTS) enhances and WT1 (+KTS) suppresses transcription.