Karolinska Institute, Department of Neuroscience, Stockholm, Sweden.
J Cell Sci. 2009 Dec 15;122(Pt 24):4547-57. doi: 10.1242/jcs.058263. Epub 2009 Nov 24.
The success of acrosomal exocytosis, a complex process with a variety of inter-related steps, relies on the coordinated interaction of participating signaling molecules. Since the acrosome reaction resembles Ca(2+)-regulated exocytosis in neurons, we investigated whether cognate neuronal binding partners of the multi-PDZ domain protein MUPP1, which recruits molecules that control the initial tethering and/or docking between the acrosomal vesicle and the plasma membrane, are also expressed in spermatozoa, and whether they contribute to the regulation of acrosomal secretion. We observed that CaMKIIalpha colocalizes with MUPP1 in the acrosomal region of epididymal spermatozoa where the kinase selectively binds to a region encompassing PDZ domains 10-11 of MUPP1. Furthermore, we found that pre-treating mouse spermatozoa with a CaMKII inhibitor that directly blocks the catalytic region of the kinase, as well as a competitive displacement of CaMKIIalpha from PDZ domains 10-11, led to a significant increase in spontaneous acrosomal exocytosis. Since Ca(2+)-calmodulin releases CaMKIIalpha from the PDZ scaffolding protein, MUPP1 represents a central signaling platform to dynamically regulate the assembly and disassembly of binding partners pertinent to acrosomal secretion, thereby precisely adjusting an increase in Ca(2+) to synchronized fusion pore formation.
顶体反应类似于神经元中 Ca(2+)-调节的胞吐作用，因此我们研究了多 PDZ 域蛋白 MUPP1 的同源神经元结合伴侣是否也在精子中表达，以及它们是否参与调节顶体分泌。我们观察到 CaMKIIalpha 与 MUPP1 在附睾精子的顶体区域共定位，激酶选择性地结合到包含 MUPP1 的 PDZ 结构域 10-11 的区域。此外，我们发现用 CaMKII 抑制剂预处理小鼠精子，该抑制剂直接阻断激酶的催化区域，以及竞争性地将 CaMKIIalpha 从 PDZ 结构域 10-11 上置换，会导致自发顶体 exocytosis 显著增加。由于 Ca(2+)-钙调蛋白将 CaMKIIalpha 从 PDZ 支架蛋白中释放出来，因此 MUPP1 代表了一个中央信号平台，可动态调节与顶体分泌相关的结合伴侣的组装和拆卸，从而精确地调整 Ca(2+)的增加以实现融合孔的同步形成。
