Tumor necrosis factor inhibits growth hormone-mediated gene expression in hepatocytes
Tumor necrosis factor inhibits growth hormone-mediated gene expression in hepatocytes
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DOI：
10.1152/ajpgi.00550.2005
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发表时间：
2006-07-01
影响因子：
4.5
通讯作者：
Cooney, Robert N.
中科院分区：
文献类型：
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作者：
Ahmed, Tamer;Yumet, Gladys;Cooney, Robert N.
生长激素 (GH) 通过 JAK2 刺激 STAT5 磷酸化，从而激活 IGF-I 和丝氨酸蛋白酶抑制剂 2.1 (Spi 2.1) 转录，而蛋白酪氨酸磷酸酶 (PTP) 使 STAT5 去磷酸化终止该信号。我们假设 TNF 对 GH 信号传导和基因转录的抑制作用是导致肝脏 GH 抵抗的原因。在 GH 刺激之前，用 TNF、过钒酸盐（一种 PTP 抑制剂）或两者处理 CWSV-1 肝细胞。测量总的和酪氨酸磷酸化的JAK2、STAT5、ERK1/2、SHP-1和SHP-2、IGF-I和Spi 2.1 mRNA水平。 GH 刺激 STAT5 和 ERK1/2 磷酸化、IGF-I 和 Spi 2.1 mRNA 表达。 GH 刺激后，TNF 减弱 JAK2/STAT5 和 ERK1/2 磷酸化以及 IGF-I 和 Spi 2.1 mRNA 表达。 TNF 或 GH 不会改变 SHP-1 和 SHP-2 蛋白水平，并且 TNF 不会进一步增加 GH 诱导的 SHP-1 PTP 活性增加。在 TNF 处理的细胞中，过钒酸盐在 GH 刺激后将 STAT5 和 ERK1/2 磷酸化恢复至对照水平，但没有恢复 IGF-I 或 Spi 2.1 mRNA 诱导。经 Spi 2.1 启动子-荧光素酶载体转染的细胞在 GH 刺激或与组成型活性 STAT5 载体共转染后，荧光素酶活性诱导了 50 倍。 TNF 阻止 GH 和 STAT5 构建体诱导 Spi 2.1 启动子活性。我们得出的结论是，TNF 不会通过诱导 SHP-1 或 -2 表达来抑制 GH 活性，并且用过钒酸盐纠正 TNF 处理的细胞中的 GH 信号传导缺陷不会恢复 GH 诱导的基因表达。 TNF 对 GH 介导的基因转录的抑制作用似乎与 STAT5 活性和先前发现的 JAK2/STAT5 信号传导异常无关。
Growth hormone (GH) stimulates STAT5 phosphorylation by JAK2, which activates IGF-I and serine protease inhibitor 2.1 (Spi 2.1) transcription, whereas STAT5 dephosphorylation by protein tyrosine phosphatases (PTPs) terminates this signal. We hypothesized that the inhibitory effects of TNF on GH signaling and gene transcription were responsible for hepatic GH resistance. CWSV-1 hepatocytes were treated with TNF, pervanadate ( a PTP inhibitor), or both, before GH stimulation. Total and tyrosine- phosphorylated JAK2, STAT5, ERK1/2, SHP-1 and SHP-2, IGF-I, and Spi 2.1 mRNA levels were measured. GH stimulated STAT5 and ERK1/2 phosphorylation, IGF-I, and Spi 2.1 mRNA expression. TNF attenuated JAK2/STAT5 and ERK1/2 phosphorylation and IGF-I and Spi 2.1 mRNA expression following GH stimulation. SHP-1 and SHP-2 protein levels were unaltered by TNF or GH, and the GH-induced increase in SHP-1 PTP activity was not further increased by TNF. In TNF-treated cells, pervanadate restored STAT5 and ERK1/2 phosphorylation to control levels following GH stimulation but did not restore IGF-I or Spi 2.1 mRNA induction. Cells transfected with a Spi 2.1 promoter- luciferase vector demonstrate a 50-fold induction in luciferase activity following GH stimulation or cotransfection with a constitutively active STAT5 vector. TNF prevented the induction of Spi 2.1 promoter activity by GH and the STAT5 construct. We conclude that TNF does not inhibit GH activity by inducing SHP-1 or -2 expression and that correction of GH signaling defects in TNF- treated cells by pervanadate does not restore GH- induced gene expression. The inhibitory effects of TNF on GH- mediated gene transcription appear independent of STAT5 activity and previously identified abnormalities in JAK2/STAT5 signaling.