The Significance of the Bifunctional Kinase/Phosphatase Activities of Diphosphoinositol Pentakisphosphate Kinases (PPIP5Ks) for Coupling Inositol Pyrophosphate Cell Signaling to Cellular Phosphate Homeostasis
The Significance of the Bifunctional Kinase/Phosphatase Activities of Diphosphoinositol Pentakisphosphate Kinases (PPIP5Ks) for Coupling Inositol Pyrophosphate Cell Signaling to Cellular Phosphate Homeostasis
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DOI：
10.1074/jbc.m116.765743
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发表时间：
2017-03-10
影响因子：
4.8
通讯作者：
Shears, Stephen B.
中科院分区：
文献类型：
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作者：
Gu, Chunfang;Nguyen, Hoai-Nghia;Shears, Stephen B.
负责 Pi 稳态的蛋白质对所有生命都至关重要。在酿酒酵母中，细胞外 [P-1] 被肌醇六磷酸激酶 (IP6K)“感知”，该激酶合成细胞内肌醇焦磷酸 5-二磷酸肌醇 1,2,3,4,6-五磷酸 (5-InsP(7))，如下所示：在 Pi 饥饿期间，细胞 [ATP] 下降； IP6K 对 ATP 的异常低亲和力迫使 5-InsP(7) 水平平行下降（Azevedo, C. 和 Saiardi, A. (2017) Trends. Biochem. Sci. 42, 219-231。迄今为止，这种 P-1 感应尚未在后生动物中得到记录。在这里，使用人肠上皮细胞系 (HCT116)，我们显示5-InsP(7) 和 ATP 在 [P-1] 饥饿时减少，随后在 Pi 补充期间恢复，然而，单独的肌醇焦磷酸，1,5-二磷酸肌醇 2,3,4,6-四磷酸 (InsP(8)) 反应更剧烈（即具有更宽的动态范围和更高的灵敏度）为了了解这种新型 InsP(8) 响应，我们表征了双功能的动力学特性。全长二磷酸肌醇五磷酸激酶 (PPIP5Ks) 的 5-InsP(7) 激酶/InsP(8) 磷酸酶活性这些数据满足先前发布的任何双功能激酶/磷酸酶表现出浓度稳健性的标准，允许激酶产物（在本例中为 InsP(8)）的水平独立于不同的前体（即 5-InsP(7)）库大小而波动。 PPIP5K 的 InsP(8) 磷酸酶活性受到 P-1 的强烈抑制（在 0-1 mM 范围内抑制 40-90%），对于 PPIP5K2，P-1 在 0-5 mM 范围内将 5-InsP(7) 激酶活性激活 2 倍，从而放大 P-1 感应。总体而言，我们的数据揭示了有助于肌醇焦磷酸特异性的机制。信号传导，独立于 5-InsP(7) 调节 InsP(8) 周转，以响应细胞外关键营养素供应的波动。
Proteins responsible for Pi homeostasis are critical for all life. In Saccharomyces cerevisiae, extracellular [P-1] is "sensed" by the inositol-hexakisphosphate kinase (IP6K) that synthesizes the intracellular inositol pyrophosphate 5-diphosphoinositol 1,2,3,4,6-pentakisphosphate (5-InsP(7)) as follows: during a period of Pi starvation, there is a decline in cellular [ATP]; the unusually low affinity of IP6Ks for ATP compels 5-InsP(7) levels to fall in parallel (Azevedo, C.,and Saiardi, A. (2017) Trends. Biochem. Sci. 42, 219-231. Hitherto, such P-1 sensing has not been documented in metazoans. Here, using a human intestinal epithelial cell line (HCT116), we show that levels of both 5-InsP(7) and ATP decrease upon [P-1] starvation and subsequently recover during Pi replenishment. However, a separate inositol pyrophosphate, 1,5-bisdiphosphoinositol 2,3,4,6-tetrakisphosphate (InsP(8)), reacts more dramatically (i.e. with a wider dynamic range and greater sensitivity). To understand this novel InsP(8) response, we characterized kinetic properties of the bifunctional 5-InsP(7) kinase/InsP(8) phosphatase activities of full-length diphosphoinositol pentakisphosphate kinases (PPIP5Ks). These data fulfil previously published criteria for any bifunctional kinase/phosphatase to exhibit concentration robustness, permitting levels of the kinase product (InsP(8) in this case) to fluctuate independently of varying precursor (i.e. 5-InsP(7)) pool size. Moreover, we report that InsP(8) phosphatase activities of PPIP5Ks are strongly inhibited by P-1 (40-90% within the 0-1 mM range). For PPIP5K2, P-1 sensing by InsP(8) is amplified by a 2-fold activation of 5-InsP(7) kinase activity by P-1 within the 0-5 mM range. Overall, our data reveal mechanisms that can contribute to specificity in inositol pyrophosphate sig-naling, regulating InsP(8) turnover independently of 5-InsP(7), in response to fluctuations in extracellular supply of a key nutrient.