Protein Serine/Threonine Phosphatase Ptc2p Negatively Regulates the Unfolded-Protein Response by Dephosphorylating Ire1p Kinase
Protein Serine/Threonine Phosphatase Ptc2p Negatively Regulates the Unfolded-Protein Response by Dephosphorylating Ire1p Kinase
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DOI：
10.1128/mcb.18.4.1967
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发表时间：
1998-04
影响因子：
5.3
通讯作者：
A. Welihinda;W. Tirasophon;S. R. Green;R. Kaufman
中科院分区：
文献类型：
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作者：
A. Welihinda;W. Tirasophon;S. R. Green;R. Kaufman
细胞通过增加编码内质网内伴侣蛋白的基因转录来响应内质网（ER）中未折叠蛋白的积累。Ire1p是一种跨膜蛋白激酶，通过其胞质核质激酶结构域的寡聚化和反式自磷酸化的机制传递内质腔内未折叠蛋白的信号。Ire1p的激活诱导了一种新的hac1 mRNA剪接形式，产生Hac1p， Hac1p是一种转录因子，是激活未折叠蛋白反应（UPR）元件控制下的基因转录所必需的。在酿酒酵母中寻找与Ire1p相互作用的蛋白，我们分离到了编码2C型丝氨酸/苏氨酸磷酸酶的PTC2。Ptc2p与Ire1p的相互作用是特异性的，直接的，依赖于Ire1p的磷酸化，并通过Ptc2p内的激酶相互作用域介导。Ptc2p在体外以Mg2+依赖的方式有效地使Ire1p去磷酸化。PTC2对生长不是必需的，并负向调节UPR通路。携带ptc2空等位基因的菌株UPR增加了三到四倍，剪接的HAC1 mRNA水平也增加了。野生型Ptc2p但不具有催化活性的Ptc2p过表达会降低剪接hac1 mRNA的水平并减弱UPR，这表明Ptc2p的磷酸酶活性是UPR调控所必需的。这些结果表明，Ptc2p通过去磷酸化Ire1p来下调UPR，并揭示了HAC1 mRNA剪接事件上游UPR通路的一种新的调控机制。
ABSTRACT Cells respond to the accumulation of unfolded proteins in the endoplasmic reticulum (ER) by increasing the transcription of the genes encoding ER-resident chaperone proteins. Ire1p is a transmembrane protein kinase that transmits the signal from unfolded proteins in the lumen of the ER by a mechanism that requires oligomerization andtrans-autophosphorylation of its cytoplasmic-nucleoplasmic kinase domain. Activation of Ire1p induces a novel spliced form ofHAC1 mRNA that produces Hac1p, a transcription factor that is required for activation of the transcription of genes under the control of the unfolded-protein response (UPR) element. Searching for proteins that interact with Ire1p in Saccharomyces cerevisiae, we isolated PTC2, which encodes a serine/threonine phosphatase of type 2C. The Ptc2p interaction with Ire1p is specific, direct, dependent on Ire1p phosphorylation, and mediated through a kinase interaction domain within Ptc2p. Ptc2p dephosphorylates Ire1p efficiently in an Mg2+-dependent manner in vitro. PTC2 is nonessential for growth and negatively regulates the UPR pathway. Strains carrying null alleles ofPTC2 have a three- to fourfold-increased UPR and increased levels of spliced HAC1 mRNA. Overexpression of wild-type Ptc2p but not catalytically inactive Ptc2p reduces levels of splicedHAC1 mRNA and attenuates the UPR, demonstrating that the phosphatase activity of Ptc2p is required for regulation of the UPR. These results demonstrate that Ptc2p downregulates the UPR by dephosphorylating Ire1p and reveal a novel mechanism of regulation in the UPR pathway upstream of the HAC1 mRNA splicing event.