Vasilyev Vyacheslav V, Lawson Mark A, Dipaolo Donna, Webster Nicholas J G, Mellon Pamela L
Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093-0674, USA.
Endocrinology. 2002 Sep;143(9):3414-26. doi: 10.1210/en.2001-211215.
GnRH regulates pituitary gonadotropin gene expression through GnRH receptor activation of the protein kinase C (PKC) and calcium signaling cascades. The pulsatile pattern of GnRH release is crucial for induction of LHbeta-subunit (LHbeta) gene expression; however, continuous prolonged GnRH exposure leads to repression of LHbeta gene transcription. Although in part, long-term repression may be due to receptor down-regulation, the molecular mechanisms of this differential regulation of LHbeta transcription are unknown. Using transfection into the LH-secreting immortalized mouse gonadotrope cell line (LbetaT4), we have demonstrated that LHbeta gene transcription is increased by acute activation (6 h) of GnRH receptor or PKC but not calcium influx; in contrast long-term activation (24 h) of GnRH receptor, PKC, or calcium influx each repress LHbeta transcription. Whereas blockade of PKC prevented the acute action of GnRH and unmasked an acute repression of LHbeta transcription by calcium, it did not prevent long-term repression by GnRH or calcium. Removal of calcium resulted in potentiation of acute GnRH and PKC induction of LHbeta gene expression but prevented long-term repression by GnRH and reduced long-term repression by either calcium or 12-O-tetradecanoyl-phorbol-13-acetate (TPA). We conclude that GnRH uses PKC for acute induction, and calcium signaling is responsible for long-term repression of LHbeta gene expression by GnRH. Furthermore, analysis of the responsiveness of truncated and mutated LHbeta promoter regions demonstrated that not only do acute induction and long-term repression use different signaling systems, but they also use different target sequences for regulating the LHbeta gene.
促性腺激素释放激素（GnRH）通过激活蛋白激酶C（PKC）和钙信号级联反应来调节垂体促性腺激素基因的表达。GnRH释放的脉冲模式对于诱导促黄体生成素β亚基（LHβ）基因表达至关重要；然而，持续长时间暴露于GnRH会导致LHβ基因转录受到抑制。虽然长期抑制部分可能是由于受体下调，但这种LHβ转录差异调节的分子机制尚不清楚。通过转染到分泌LH的永生化小鼠促性腺激素细胞系（LβT4）中，我们已经证明，GnRH受体或PKC的急性激活（6小时）可增加LHβ基因转录，但钙内流则不能；相反，GnRH受体、PKC或钙内流的长期激活（24小时）均会抑制LHβ转录。虽然阻断PKC可阻止GnRH的急性作用，并揭示钙对LHβ转录的急性抑制作用，但它并不能阻止GnRH或钙的长期抑制作用。去除钙会增强GnRH和PKC对LHβ基因表达的急性诱导作用，但可阻止GnRH的长期抑制作用，并减少钙或12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯（TPA）的长期抑制作用。我们得出结论，GnRH利用PKC进行急性诱导，而钙信号负责GnRH对LHβ基因表达的长期抑制。此外，对截短和突变的LHβ启动子区域反应性的分析表明，不仅急性诱导和长期抑制使用不同的信号系统，而且它们还使用不同的靶序列来调节LHβ基因。
