Departamento de Biología Celular, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Avenida Instituto Politécnico Nacional 2508, San Pedro Zacatenco, México DF 07360, Mexico.
Reproduction. 2012 Jul;144(1):123-34. doi: 10.1530/REP-11-0433. Epub 2012 May 17.
In the mammalian sperm, the acrosome reaction (AR) is considered to be a regulated secretion that is an essential requirement for physiological fertilization. The AR is the all-or-nothing secretion system that allows for multiple membrane fusion events. It is a Ca(2)(+)-regulated exocytosis reaction that has also been shown to be regulated by several signaling pathways. CDC42 has a central role in the regulated exocytosis through the activation of SNARE proteins and actin polymerization. Furthermore, the lipid raft protein caveolin-1 (CAV1) functions as a scaffold and guanine nucleotide dissociation inhibitor protein for CDC42, which is inactivated when associated with CAV1. CDC42 and other RHO proteins have been shown to localize in the acrosome region of mammalian sperm; however, their relationship with the AR is unknown. Here, we present the first evidence that CDC42 and CAV1 could be involved in the regulation of capacitation and the AR. Our findings show that CDC42 is activated early during capacitation, reaching an activation maximum after 20 min of capacitation. Spontaneous and progesterone-induced ARs were inhibited when sperm were capacitated in presence of secramine A, a specific CDC42 inhibitor. CAV1 and CDC42 were co-immunoprecipitated from the membranes of noncapacitated sperm; this association was reduced in capacitated sperm, and our data suggest that the phosphorylation (Tyr14) of CAV1 by c-Src is involved in such reductions. We suggest that CDC42 activation is favored by the disruption of the CAV1-CDC42 interaction, allowing for its participation in the regulation of capacitation and the AR.
在哺乳动物精子中，顶体反应（AR）被认为是一种受调控的分泌过程，是生理受精的必要条件。AR 是一种全或无的分泌系统，允许发生多次膜融合事件。它是一种 Ca(2)(+) 调控的胞吐反应，也被证明受到几种信号通路的调节。CDC42 通过激活 SNARE 蛋白和肌动蛋白聚合在调控的胞吐作用中起核心作用。此外，脂质筏蛋白 caveolin-1（CAV1）作为 CDC42 的支架和鸟嘌呤核苷酸解离抑制剂蛋白发挥作用，当与 CAV1 相关联时，CDC42 被失活。CDC42 和其他 RHO 蛋白已被证明定位于哺乳动物精子的顶体区域；然而，它们与 AR 的关系尚不清楚。在这里，我们首次提供证据表明 CDC42 和 CAV1 可能参与调节顶体化和 AR。我们的研究结果表明，CDC42 在顶体化早期被激活，在顶体化 20 分钟后达到激活最大值。当精子在 secramine A（一种特异性 CDC42 抑制剂）存在下进行顶体化时，自发和孕酮诱导的 AR 被抑制。CAV1 和 CDC42 从未顶体化精子的膜中共同免疫沉淀；这种结合在顶体化精子中减少，我们的数据表明，c-Src 对 CAV1 的酪氨酸 14 磷酸化（Tyr14）参与了这种减少。我们认为，CDC42 的激活得益于 CAV1-CDC42 相互作用的破坏，从而允许其参与顶体化和 AR 的调节。
