Interactions between kinases and phosphatases in the rapid control of brain aromatase
Interactions between kinases and phosphatases in the rapid control of brain aromatase
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DOI：
10.1111/j.1365-2826.2005.01344.x
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发表时间：
2005-09-01
影响因子：
3.2
通讯作者：
Ball, GF
中科院分区：
文献类型：
--
作者：
Balthazart, J;Baillien, M;Ball, GF
睾酮芳构化成雌二醇在许多脊椎动物雄性性行为的激活中起着关键作用。脑芳香化酶活性的快速变化最近被发现，由此导致的局部雌激素生物利用度的变化可以调节对雌激素的快速行为反应。在鹌鹑下丘脑匀浆中，在ATP、MgCl2和CaCl2 （ATP/Mg/Ca）存在的情况下，芳香酶活性在几分钟内被钙依赖性磷酸化下调。三种激酶（蛋白激酶A、C和钙调蛋白激酶；PKA、PKC和CAMK）可能参与了这一过程。如果激酶以可逆的方式降低芳香化酶的活性，那么在磷酸酶存在的情况下，酶的活性将会增加和/或恢复到基线水平。我们之前的研究表明，0.1 mM钒酸盐（一种普通的蛋白磷酸酶抑制剂）会显著降低芳香化酶的活性，但迄今为止还没有发现能够上调芳香化酶活性的特异性蛋白磷酸酶。以碱性磷酸酶和酸性磷酸酶（Alk和Ac）为研究对象，探讨了磷酸化对芳香化酶活性抑制的可逆性。出乎意料的是，Alk PPase在存在和不存在ATP/Mg/Ca的情况下以剂量依赖的方式抑制芳香化酶活性。相比之下，Ac PPase完全阻断了ATP/Mg/Ca对芳香化酶活性的抑制作用，即使它在没有ATP/Mg/Ca的情况下适度抑制芳香化酶活性。然而，在暴露于ATP/Mg/Ca环境后，添加Ac PPase无法恢复芳香化酶的活性。综上所述，这些数据表明，在鹌鹑芳香化酶序列中确定的15个潜在的共识磷酸化位点中，一些位点必须被组成性磷酸化才能使酶具有活性，而其他位点的磷酸化则参与了蛋白激酶和磷酸酶的竞争作用对芳香化酶活性的快速抑制。在这15个假定的磷酸化位点中，有两个发生在与PKC、PKA（可能还有CAMK）的共识位点相对应的环境中，并且很可能代表了磷酸化迅速阻断酶活性的位点。
Aromatization of testosterone into oestradiol plays a key role in the activation of male sexual behaviour in many vertebrate species. Rapid changes in brain aromatase activity have recently been identified and the resulting changes in local oestrogen bioavailability could modulate fast behavioural responses to oestrogens. In quail hypothalamic homogenates, aromatase activity is down-regulated within minutes by calcium-dependent phosphorylations in the presence of ATP, MgCl2 and CaCl2 (ATP/Mg/Ca). Three kinases (protein kinases A and C and calmodulin kinase; PKA, PKC and CAMK) are potentially implicated in this process. If kinases decrease aromatase activity in a reversible manner, then it would be expected that the enzymatic activity would increase and/or return to baseline levels in the presence of phosphatases. We showed previously that 0.1 mM vanadate (a general inhibitor of protein phosphatases) significantly decreases aromatase activity but specific protein phosphatases that could up-regulate aromatase activity have not been identified to date. The reversibility of aromatase activity inhibition by phosphorylations was investigated in the present study using alkaline and acid phosphatase (Alk and Ac PPase). Unexpectedly, Alk PPase inhibited aromatase activity in a dose-dependent manner in the presence, as well as in the absence, of ATP/Mg/Ca. By contrast, Ac PPase completely blocked the inhibitory effects of ATP/Mg/Ca on aromatase activity, even if it moderately inhibited aromatase activity in the absence of ATP/Mg/Ca. However, the addition of Ac PPase was unable to restore aromatase activity after it had been inhibited by exposure to ATP/Mg/Ca. Taken together, these data suggest that, amongst the 15 potential consensus phosphorylation sites identified on the quail aromatase sequence, some must be constitutively phosphorylated for the enzyme to be active whereas phosphorylation of the others is involved in the rapid inhibition of aromatase activity by the competitive effects of protein kinases and phosphatases. Two out of these 15 putative phosphorylation sites occur in an environment corresponding to the consensus sites for PKC, PKA (and possibly a CAMK) and, in all probability, represent the sites whose phosphorylation rapidly blocks enzyme activity.