A density-sensing factor regulates signal transduction in Dictyostelium.
A density-sensing factor regulates signal transduction in Dictyostelium.
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DOI：
10.1083/jcb.129.5.1251
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发表时间：
1995-06
期刊：
影响因子：
--
通讯作者：
Gomer RH
中科院分区：
文献类型：
--
作者：
Yuen IS;Jain R;Bishop JD;Lindsey DF;Deery WJ;Van Haastert PJ;Gomer RH
盘基网眼菌在细胞过度生长并饥饿时开始发育。为了协调发育，细胞监测饥饿细胞分泌的一种蛋白质--条件介质因子(CMF)的胞外水平。当给定区域中的大多数细胞已经饥饿时，如CMF分泌所示，CMF的胞外水平上升到阈值以上，并允许饥饿的细胞聚集。这些细胞使用传递的cAMP脉冲作为化学吸引剂进行聚集。反义阻断CMF积累的细胞中，除非存在外源性CMF，否则不会聚集。我们发现这些细胞是有活性的，但不会对cAMP产生趋化作用。视频显微镜显示，CMF反义细胞不能产生化学税并不是由于运动能力的严重缺陷，尽管视频和扫描电子显微镜都表明CMF增加了伪足形成的频率。在缺乏CMF的细胞中，钙离子内流、腺苷环化酶和鸟苷酸环化酶对cAMP脉冲的激活受到强烈抑制，但仅10 S暴露于CMF就可使其恢复。CMF不影响cAMP对磷脂酶C的激活作用。Northern杂交显示在发育过程中CMF反义细胞中cAMP受体mRNA的正常水平，而cAMP结合分析和Scatchard图表明CMF反义细胞中含有正常水平的cAMP受体。在网柄苔藓中，腺苷和鸟苷酸环化酶都是通过G蛋白激活的。我们发现cAMP受体与G蛋白在体外的相互作用不受CMF的明显影响，而G蛋白激活腺苷环化酶则需要细胞暴露在CMF中。因此，CMF似乎通过调节cAMP信号转导的早期步骤来调节聚集。
Dictyostelium discoideum initiates development when cells overgrow their bacterial food source and starve. To coordinate development, the cells monitor the extracellular level of a protein, conditioned medium factor (CMF), secreted by starved cells. When a majority of the cells in a given area have starved, as signaled by CMF secretion, the extracellular level of CMF rises above a threshold value and permits aggregation of the starved cells. The cells aggregate using relayed pulses of cAMP as the chemoattractant. Cells in which CMF accumulation has been blocked by antisense do not aggregate except in the presence of exogenous CMF. We find that these cells are viable but do not chemotax towards cAMP. Videomicroscopy indicates that the inability of CMF antisense cells to chemotax is not due to a gross defect in motility, although both video and scanning electron microscopy indicate that CMF increases the frequency of pseudopod formation. The activations of Ca2+ influx, adenylyl cyclase, and guanylyl cyclase in response to a pulse of cAMP are strongly inhibited in cells lacking CMF, but are rescued by as little as 10 s exposure of cells to CMF. The activation of phospholipase C by cAMP is not affected by CMF. Northern blots indicate normal levels of the cAMP receptor mRNA in CMF antisense cells during development, while cAMP binding assays and Scatchard plots indicate that CMF antisense cells contain normal levels of the cAMP receptor. In Dictyostelium, both adenylyl and guanylyl cyclases are activated via G proteins. We find that the interaction of the cAMP receptor with G proteins in vitro is not measurably affected by CMF, whereas the activation of adenylyl cyclase by G proteins requires cells to have been exposed to CMF. CMF thus appears to regulate aggregation by regulating an early step of cAMP signal transduction.