Caspase-3对磷酸化tau蛋白截断作用的研究

Truncation of Caspase-3 on Phosphorylated tau

磷酸化tau是阿尔茨海默病(Alzheimer蒺s disease,AD) 的特征性病理改变——神经原纤维缠结(neurofibrillary tangles,NFTs) 的主要组成部分. 最近的研究显示:NFT存在Glu391和Asp421位点被截断的tau片段,然而,tau蛋白的磷酸化是否会影响caspase-3的切割作用尚不清楚. 首先纯化重组tau 蛋白,然后利用蛋白激酶A (PKA)、钙/钙调蛋白依赖性蛋白激酶Ⅱ(CaMKⅡ)和乳鼠海马组织抽提液对其磷酸化,并用caspase-3对不同磷酸化的tau 蛋白进行切割,比较caspase-3对非磷酸化和不同蛋白激酶磷酸化的tau 蛋白的切割特性. 结果显示:除切割非磷酸化tau蛋白外,caspase-3在体外可分别切割被PKA、CaMKⅡ和乳鼠海马组织抽提液磷酸化的tau蛋白. 这一结果提示:磷酸化修饰的tau蛋白仍然是caspase-3的底物.

It is reported recently that truncated tau at Glu391 and Asp421 presents in the patients of Alzheimer's disease (AD) brain, and caspase-3 is involved in tau truncation at Asp421. In vitro studies show that caspase-3 can cleaved tau only at Asp421 and the proteolytic cleavage of tau at Asp421 by caspase-3 generates a truncated tau fragment namely taul-421, which enhances filament assembly in vitro. Expression of taul-421 in neurons promotes apoptosis. It is not known that if phosphorylated tau is also a substrate of caspase-3. To understand the question, recombinant human tau protein was purified and phosphorylated with protein kinase A (PKA), calcium/calmodulin dependent protein kinase II (CaMK II) or kinases from newborn rat hippocampi extract, and then these different tau species were cleaven by caspase-3. It was demonstrated that tau phosphorylated by PKA, CaMK II and newborn hippocampi extract is also cleaven by caspase-3. As the phosphorylated tau also can be cleaven by caspase-3, it was speculated that phosphorylation tau is still the substrate of caspase-3.