The cAMP signaling system regulates LHβ gene expression:: roles of early growth response protein-1 SP1 and steroidogenic factor-1
The cAMP signaling system regulates LHβ gene expression:: roles of early growth response protein-1 SP1 and steroidogenic factor-1
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DOI：
10.1677/jme.0.0320291
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发表时间：
2004-02-01
影响因子：
3.5
通讯作者：
Halvorson, LM
中科院分区：
文献类型：
--
作者：
Horton, CD;Halvorson, LM
促性腺激素基因的表达已被证明是由蛋白激酶C（PKC）和cAMP第二信使信号通路的药理学或生理学激活剂调节。在过去的几年中，在LH β亚基（LH β）基因中介导PKC反应的转录因子和同源顺式元件的鉴定和表征方面取得了大量进展。相反，很少有人知道有关的分子机制，介导cAMP介导的调节该基因。使用垂体细胞系，我们现在证明，大鼠LH β基因启动子活性刺激后激活的cAMP系统的腺苷酸环化酶激活剂，毛喉素，或肽，垂体腺苷酸环化酶激活肽。当在LH β基因的区域-207/+5的背景下进行评价时，通过先前鉴定的早期生长反应蛋白-1（Egr-1）的3'顺式作用元件的突变消除了毛喉素反应。cAMP系统的激活增加了Egr-1基因启动子活性、Egr-1蛋白水平和Egr-1与LH β基因启动子的结合，支持了该转录因子在介导cAMP应答中的作用。对较长的LH β启动子构建体（-797/+5）的分析揭示了上游Sp1 DNA调控区的额外贡献。感兴趣的是，观察到毛喉素诱导的LH β基因启动子活性的刺激与转录因子类固醇生成因子-1（SF-1）的引入协同增加。虽然SF-1是其他基因中cAMP反应的关键介质，但大鼠LH β基因中SF-1 DNA结合位点的突变并没有改变毛喉素反应，也没有增加促性腺细胞系中SF-1蛋白水平。在另一组实验中，确定了在先前定义的同源框结合元件在位置-100处突变后，毛喉素反应性得以维持。我们的结论是，Egr-1和Sp1有助于cAMP依赖性转录的大鼠LH β基因启动子。虽然SF-1不能独立地介导cAMP/PKA反应，但SF-1对放大这种反应很重要。
Expression of the gonadotropin genes has been shown to be modulated by pharmacological or physiological activators of both the protein kinase C (PKC) and the cAMP second messenger signaling pathways. Over the past few years, a substantial amount of progress has been made in the identification and characterization of the transcription factors and cognate cis-elements which mediate the PKC response in the LH beta-subunit (LHbeta) gene. In contrast, little is known regarding the molecular mechanisms which mediate cAMP-mediated regulation of this gene. Using pituitary cell lines, we now demonstrate that rat LHbeta gene promoter activity is stimulated following activation of the cAMP system by the adenylate cyclase activating agent, forskolin, or by the peptide, pituitary adenylate cyclase-activating peptide. The forskolin response was eliminated with mutation of a previously identified 3' cis-acting element for the early growth response protein-1 (Egr-1) when evaluated in the context of region -207/+5 of the LHbeta gene. Activation of the cAMP system increased Egr-1 gene promoter activity, Egr-1 protein levels and Egr-1 binding to the LHbeta gene promoter, supporting the role of this transcription factor in mediating the cAMP response. Analysis of a longer LHbeta promoter construct (-797/+5) revealed additional contribution by upstream Sp1 DNA-regulatory regions. Of interest, forskolin-induced stimulation of LHbeta gene promoter activity was observed to increase synergistically with introduction of the transcription factor, steroidogenic factor-1 (SF-1). Although SF-1 is a critical mediator of the cAMP response in other genes, mutation of the SF-1 DNA-binding sites in the rat LHbeta gene did not alter the forskolin response nor did forskolin increase SF-1 protein levels in a gonadotrope cell line. In a further set of experiments, it was determined that forskolin-responsiveness was maintained following mutation of the previously defined homeobox-binding element at position -100. We conclude that both Egr-1 and Sp1 contribute to cAMP-dependent transcription of the rat LHbeta gene promoter. While SF-1 does not act independently to mediate the cAMP/PKA response, SF-1 is important for magnification of this response.