The Mina and Everard Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel.
Dev Biol. 2010 Aug 15;344(2):650-7. doi: 10.1016/j.ydbio.2010.05.490. Epub 2010 May 24.
The sperm acrosome reaction occurs after the binding of the capacitated sperm to the egg zona pellucida. This study describes a novel mode of regulation of the sperm epidermal growth factor receptor (EGFR) under physiological conditions and its relevance to the acrosome reaction. Ouabain, a known Na/K ATPase blocker is present in the blood and in the female reproductive tract. We show here that physiological concentrations (nM) of ouabain enhance phosphorylation of EGFR on tyr-845, stimulate Ca(2+) influx and induce the acrosome reaction in sperm. These effects could be seen only in the presence of very low concentrations of EGF (0.1 ng/ml or 0.016 nM) added together with nano-molar ouabain. Phosphorylation, Ca(2+) influx, and the acrosome reaction are inhibited by an EGFR blocker, suggesting that trans-activation of the EGFR is involved. Moreover, our data revealed that protein kinase A and the family of tyrosine kinase, SRC, shown before to be involved in EGFR activation in sperm, mediate the acrosome reaction induced by ouabain. Ouabain alone (without EGF) at relatively high concentration (10microM) could enhance EGFR phosphorylation, Ca(2+) influx and acrosome reaction, and these processes were inhibited by EGFR blockers. Moreover, we show here that PKA and SRC family are involved in the activation of EGFR by 10 microM ouabain, further demonstrating that ouabain induces the acrosome reaction by a mechanism mediated by the trans-activation of EGFR. In conclusion, this study describes an interesting regulatory path of EGFR by physiological concentrations of ouabain and EGF found in the female reproductive tract. Neither of these compounds can activate the EGFR alone at such low physiological levels; however, when both are present, the interaction of ouabain with the Na/K ATPase leads to the priming of the EGFR, which undergoes its full activation by EGF.
精子顶体反应发生在获能精子与卵透明带结合之后。本研究描述了一种生理条件下调节精子表皮生长因子受体（EGFR）的新方式及其与顶体反应的相关性。哇巴因是一种已知的 Na+/K+ATP 酶抑制剂，存在于血液和女性生殖道中。我们在这里表明，生理浓度（nM）的哇巴因增强 EGFR 酪氨酸 845 上的磷酸化，刺激 Ca2+内流，并诱导精子顶体反应。只有在添加低浓度 EGF（0.1ng/ml 或 0.016nM）的情况下，才能观察到这些效应与纳米摩尔哇巴因一起。磷酸化、Ca2+内流和顶体反应被 EGFR 阻滞剂抑制，表明 EGFR 的转激活参与其中。此外，我们的数据表明，蛋白激酶 A 和 SRC 家族，以前被证明参与精子中 EGFR 的激活，介导了哇巴因诱导的顶体反应。哇巴因（无 EGF）单独在相对较高浓度（10μM）时可以增强 EGFR 磷酸化、Ca2+内流和顶体反应，这些过程被 EGFR 阻滞剂抑制。此外，我们在这里表明，PKA 和 SRC 家族参与 10μM 哇巴因激活 EGFR，进一步表明哇巴因通过 EGFR 转激活介导的机制诱导顶体反应。总之，本研究描述了一种有趣的生理浓度哇巴因和 EGF 调节 EGFR 的途径，这些物质在女性生殖道中都有发现。在如此低的生理水平下，这两种化合物都不能单独激活 EGFR；然而，当它们同时存在时，哇巴因与 Na+/K+ATP 酶的相互作用导致 EGFR 的启动，然后通过 EGF 使其完全激活。
