Serum Albumin Stimulates Protein Kinase G-dependent Microneme Secretion in Toxoplasma gondii
Serum Albumin Stimulates Protein Kinase G-dependent Microneme Secretion in Toxoplasma gondii
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DOI：
10.1074/jbc.m115.700518
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发表时间：
2016-04-29
影响因子：
4.8
通讯作者：
Sibley, L. David
中科院分区：
文献类型：
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作者：
Brown, Kevin M.;Lourido, Sebastian;Sibley, L. David
在顶复门寄生虫中，丝素分泌对于运动、侵入和外出是必需的。虽然以前的研究表明，Ca 2+和cGMP控制微线体分泌，很少有人知道这些途径是如何自然激活。在这里，我们已经开发了遗传编码的Ca 2+和微线分泌的指标，以更好地定义信号通路，调节这些过程中的弓形虫。我们发现，微线体分泌触发在体外暴露于一个单一的主机蛋白，血清白蛋白。天然激动剂血清白蛋白以蛋白激酶G依赖的方式诱导微线体分泌，该方式与cGMP水平增加相关。令人惊讶的是，血清白蛋白的作用独立于升高的Ca 2+，但它是增强人工激动剂，提高Ca 2+，如乙醇。此外，虽然乙醇升高细胞内Ca 2+，但在没有血清或血清白蛋白存在的情况下，乙醇本身不能触发分泌。这种二分法被扎普司特概括，扎普司特是一种磷酸二酯酶抑制剂，以蛋白激酶G-非依赖性方式升高cGMP并单独增加Ca 2+，导致微线体分泌。两者合计，这些研究结果表明，微线体分泌是由蛋白激酶G集中控制，这一途径是进一步增强细胞内Ca 2+的升高。
Microneme secretion is essential for motility, invasion, and egress in apicomplexan parasites. Although previous studies indicate that Ca2+ and cGMP control microneme secretion, little is known about how these pathways are naturally activated. Here we have developed genetically encoded indicators for Ca2+ and microneme secretion to better define the signaling pathways that regulate these processes in Toxoplasma gondii. We found that microneme secretion was triggered in vitro by exposure to a single host protein, serum albumin. The natural agonist serum albumin induced microneme secretion in a protein kinase G-dependent manner that correlated with increased cGMP levels. Surprisingly, serum albumin acted independently of elevated Ca2+ and yet it was augmented by artificial agonists that raise Ca2+, such as ethanol. Furthermore, although ethanol elevated intracellular Ca2+, it alone was unable to trigger secretion without the presence of serum or serum albumin. This dichotomy was recapitulated by zaprinast, a phosphodiesterase inhibitor that elevated cGMP and separately increased Ca2+ in a protein kinase G-independent manner leading to microneme secretion. Taken together, these findings reveal that microneme secretion is centrally controlled by protein kinase G and that this pathway is further augmented by elevation of intracellular Ca2+.