GENETIC AND PHYSIOLOGICAL MODULATION OF THE PRESTARVATION RESPONSE IN DICTYOSTELIUM-DISCOIDEUM
GENETIC AND PHYSIOLOGICAL MODULATION OF THE PRESTARVATION RESPONSE IN DICTYOSTELIUM-DISCOIDEUM
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DOI：
10.1091/mbc.6.3.311
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发表时间：
1995-03-01
影响因子：
3.3
通讯作者：
CLARKE, M
中科院分区：
文献类型：
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作者：
BURDINE, V;CLARKE, M
在整个营养生长过程中，网骨藻分泌一种自分泌因子，即饥饿前因子，PSF，其积累与细胞密度成比例。在指数生长后期，PSF诱导几种基因的表达，其产物是cAMP信号传导和细胞聚集所需的。这些基因中有盘状蛋白-I和环核苷酸磷酸二酯酶（PDE）的2.4 kb转录本。我们已经确定了几个参数，调节一个或两个这些prestarvation反应基因的表达，所有的影响进行了监测，在细胞上的细菌呈指数增长。在这些条件下，无菌突变体产生比野生型细胞更高水平的PSF活性。与高PSF水平一致，在相同的细胞密度下，2.4-kb PDE转录物在纯性菌株中比野生型细胞中更丰富。与此相反，密度依赖性诱导discoidin-I在纯菌株中大大延迟，只发生在指数增长的最后。对独立来源的纯性菌株的分析表明，这种对盘状蛋白-I表达的负面影响是由于纯性突变本身。还分析了抑制饥饿前反应的两个环境因素（细胞赖以为生的细菌和细菌产物叶酸）的影响。我们发现叶酸不能解释细菌的抑制作用。缺乏G蛋白β亚基的细胞（被认为是网骨藻中所有异源三聚体G蛋白所共有的）以与G β（+）细胞相同的方式对PSF作出反应，并且这种反应被细菌抑制。然而，叶酸对g β（-）细胞没有抑制作用，表明叶酸抑制作用是由异源三聚体G蛋白介导的。在缺乏蛋白激酶A催化亚单位的细胞中，饥饿前反应严重受损，但约3%的pka（-）细胞表现出明显正常的密度依赖性诱导discoidin-I。这种行为和野生型细胞中的饥饿前反应的异质性使我们推测蛋白激酶A可能不是PSF信号转导本身所需的，而是可能使细胞对PSF产生反应。基于腺苷酸环化酶突变体（acn（-））的分析，蛋白激酶A的作用不是cAMP依赖性的。
Throughout vegetative growth, Dictyostelium amoebae secrete an autocrine factor, prestarvation factor, PSF, which accumulates in proportion to cell density. During late exponential growth, PSF induces the expression of several genes whose products are needed for cAMP signaling and cell aggregation. Among these genes are discoidin-I and the 2.4-kb transcript of cyclic nucleotide phosphodiesterase (PDE). We have identified several parameters that modulate expression of one or both of these prestarvation response genes; all effects were monitored in cells growing exponentially on bacteria. Under these conditions, axenic mutants produce higher levels of PSF activity than wild-type cells. Consistent with the high PSF levels, the 2.4-kb PDE transcript is more abundant in axenic strains than wild-type cells at the same cell density. In contrast, the density-dependent induction of discoidin-I is greatly delayed in axenic strains, occurring only at the very end of exponential growth. Analysis of axenic strains of independent origin suggested that this negative effect on discoidin-I expression is attributable to the axenic mutations themselves. The effects of two environmental factors that inhibit the prestarvation response (the bacteria upon which the cells feed and a bacterial product, folic acid) were also analyzed. We found that folate does not account for the inhibitory effect of bacteria. Cells deficient in the G-protein beta subunit, which is thought to be common to all heterotrimeric G-proteins in Dictyostelium, respond to PSF in the same manner as G beta(+) cells, and this response is inhibited by bacteria. However, folate has no inhibitory effect on g beta(-) cells, indicating that folate inhibition is mediated by a heterotrimeric G-protein. In cells lacking the catalytic subunit of protein kinase A, the prestarvation response is severely impaired, but about 3% of the pka(-) cells manifest an apparently normal density-dependent induction of discoidin-I. This behavior and the heterogeneity of the prestarvation response in wild-type cells lead us to speculate that protein kinase A may not be required for PSF signal transduction per se, but rather may render the cells responsive to PSF. Based on analysis of adenylyl cyclase mutants (acn(-)), the effect of protein kinase A is not cAMP-dependent.