DAPK活化MARK1/2進而調控微管組合、神經分化和tau毒性

Abstract

死亡相關蛋白激酶(Death-associated protein kinase, DAPK)是一個促進死亡，由鈣/攜鈣素所調節的絲氨酸/蘇氨酸激酶。DAPK在腦內大量存在，並調節好幾種神經死亡或傷害的情況。此外，遺傳實驗發現兩個在DAPK基因座上的單核甘酸多型性(single nucleotide polymorphisms, SNPs)和遲發性阿滋海默症有高度關聯，而這兩個SNPs和對偶基因特異性表現相關，暗示DAPK的基因差異調控遲發性阿滋海默症的敏感性。已知DAPK促進細胞死亡的能力有一部分是透過肌動蛋白細胞骨架(actin cytoskeletons)，在此，我們發現DAPK會活化微管親合性調控激酶(MAP/microtubule affinity regulating kinase, MARK) 1/2，進而抑制微管組合(microtubule assembly)。已知MARK1/2會磷酸化微管相關蛋白(microtubule-associated protein, MAP)，包括MAP2/4和tau。MARK2的活性增加，也促使tau絲氨酸262殘基的磷酸化增加，進而影響 tau和微管的接合，而使tau無法繼續穩定微管，因此，DAPK促進由MARK1/2所造成的微管破壞現象。特別的是，對於活化MARK1/2，DAPK的死亡區塊(death domain)是必須且足夠的，而不需要DAPK的酵素能力。死亡區塊和MARK1/2的間隔區域(spacer region)結合，引起MARK1/2構型改變，而將它從自我抑制中釋放。因此，我們發現在DAPK基因剔除小鼠的腦組織中，絲氨酸262殘基的磷酸化會降低；也發現DAPK會促進MARK1/2功能而調控極化軸索向外生長(polarized neurite outgrowth)。利用果蠅系統，我們發現大量表現包含死亡區塊的DAPK可引起毛糙眼(rough eye)和光受器神經元(photoreceptor neuron)的流失，而這樣的現象是透過PAR-1 (MARK在果蠅的同源基因) 和tau所造成的，並和tau的絲氨酸262殘基磷酸化有關。總結，由上述的實驗，我們發現DAPK可以增進MARK1/2的激酶活性，進而調控它的生物功能，包含微管組合、神經分化、及和阿滋海默症相關的tau毒性。

Death-associated protein kinase (DAPK) is a key player in several modes of neuronal death/injury and has been implicated in the late-onset Alzheimer’s disease (AD). DAPK promotes cell death partly through its effect on regulating actin cytoskeletons. Here, we report that DAPK inhibits microtubule (MT) assembly by activating MARK/PAR-1 family kinases MARK1/2, which destabilize MT by phosphorylating tau and related MAP2/4. DAPK death domain, but not catalytic activity, is responsible for this activation by binding to MARK1/2 spacer region, thereby disrupting an intramolecular interaction that inhibits MARK1/2. Accordingly, DAPK-/- mice brain displays a reduction of tau phosphorylation and DAPK enhances the effect of MARK2 on regulating polarized neurite outgrowth. Using a well characterized Drosophila model of tauopathy, we show that DAPK acts in part through MARK Drosophila ortholog PAR-1 to induce rough eye and loss of photoreceptor neurons. Furthermore, DAPK enhances tau toxicity through a PAR-1 phosphorylation-dependent mechanism. Together, our study reveals a novel mechanism of MARK activation, uncovers DAPK functions in modulating MT assembly and neuronal differentiation, and provides a molecular link of DAPK to tau phosphorylation, an event associated with AD pathology.