Small Nuclear RING Finger Protein Stimulates the Rat Luteinizing Hormone-β Promoter by Interacting with Sp1 and Steroidogenic Factor-1 and Protects from Androgen Suppression

GnRH controls expression of the LH subunit genes, α and LHβ, with the LHβ subunit regulated most dramatically. Two enhancer regions, distal and proximal, on the rat LHβ gene promoter cooperate for full basal expression and GnRH stimulation. It has been hypothesized that the transcription factors binding to these regions, Sp1, Egr-1, and steroidogenic factor 1 (SF-1), may interact directly or indirectly via a coactivator. One such coactivator may be small nuclear RING finger protein (SNURF), which is expressed in pituitary tissue and the LβT2 gonadotrope cell line. In transfection experiments in LβT2 cells, SNURF stimulated basal expression of LHβ and increased overall GnRH stimulation. SNURF specifically stimulated LHβ, with no effect on the α-subunit promoter. SNURF interacts with Sp1 and SF-1, but not Egr-1, in pull-down experiments. Point mutations or deletions of SNURF functional domains demonstrated that Sp1 and SF-1 interactions with SNURF are required for SNURF stimulatory effects on the LHβ promoter. Endogenous SNURF is associated with the LHβ promoter on native chromatin, suggesting that it plays a physiological role in LHβ gene expression. SNURF also binds the androgen receptor, and SNURF overexpression overcomes androgen suppression of GnRH-stimulated LHβ but not αsubunit promoter activity. SNURF mutations that disrupt Sp1 or SF-1 binding eliminate rescue by SNURF. We conclude that SNURF may mediate interactions between the distal and proximal GnRH response regions of the LHβ promoter to stimulate transcription and can also protect the promoter from androgen suppression.