Activation of luteinizing hormone beta gene by gonadotropin-releasing hormone requires the synergy of early growth response-1 and steroidogenic factor-1.
We have previously shown that early growth response (Egr) 1-deficient mice exhibit female infertility, reflecting a luteinizing hormone (LH) beta deficiency. Egr-1 activates the LHbeta gene in vitro through synergy with steroidogenic factor-1 (SF-1), a protein required for gonadotrope function. To test if this synergy is essential for gonadotropin-releasing hormone (GnRH) stimulation of LHbeta, we examined the activity of the LHbeta promoter in the gonadotrope cell line LbetaT2. GnRH markedly stimulated the LHbeta promoter (15-fold). Mutation of either Egr-1 or SF-1 elements within the LHbeta promoter attenuated this stimulation, whereas mutation of both promoter elements abrogated GnRH induction of the LHbeta promoter. Furthermore, GnRH stimulated Egr-1 but not SF-1 expression in LbetaT2 cells. Importantly, overexpression of Egr-1 alone was sufficient to enhance LHbeta expression. Although other Egr proteins are expressed in LbetaT2 cells and are capable of interacting with SF-1, GnRH stimulation of Egr-1 was the most robust. We also found that the nuclear receptor DAX-1, a repressor of SF-1 activity, reduced Egr-1-SF-1 synergy and diminished GnRH stimulation of the LHbeta promoter. We conclude that the synergy between Egr-1 and SF-1 is essential for GnRH stimulation of the LHbeta gene and plays a central role in the dynamic regulation of LHbeta expression.
D000818:Animals; D002460:Cell Line; D057137:DAX-1 Orphan Nuclear Receptor; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D004357:Drug Synergism; D051766:Early Growth Response Protein 1; D005260:Female; D051717:Fushi Tarazu Transcription Factors; D005786:Gene Expression Regulation; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D018398:Homeodomain Proteins; D017874:Immediate-Early Proteins / Q000502:physiology*; D007986:Luteinizing Hormone / Q000235:genetics*; D051379:Mice; D011401:Promoter Regions, Genetic; D011673:Pulsatile Flow; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D012097:Repressor Proteins; D054339:Steroidogenic Factor 1; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D016335:Zinc Fingers