DAPK1 Signaling Pathways in Stroke from Mechanism

Authors: Shan Wang Xiangde Shi Hao Li Pei Pang Lei Pei Huiyong Shen Youming Lu

Publish Date: 2016/07/22

Volume: 54, Issue: 6, Pages: 4716-4722

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Abstract

Deathassociated protein kinase 1 DAPK1 a Ca2+/calmodulin CaMdependent serine/threonine protein kinase plays important roles in diverse apoptosis pathways not only in tumor suppression but also in neuronal cell death The requirement of DAPK1 catalytic activity for its proposed cell functions and the elevation of catalytic activity of DAPK1 in injured neurons in models of neurological diseases such as ischemia and epilepsy validate that DAPK1 can be taken as a potential therapeutic target in these diseases Recent studies show that DAPK1NR2B DAPK1DANGER DAPK1p53 and DAPK1Tau are currently known pathways in strokeinduced cell death and blocking these cascades in an acute treatment effectively reduces neuronal loss In this review we focus on the role of DAPK1 in neuronal cell death after stroke We hope to provide exhaustive summaries of relevant studies on DAPK1 signals involved in stroke damage Therefore disrupting DAPK1relevant cell death pathway could be considered as a promising therapeutic approach in strokeStroke a major cause of morbidity and mortality affects millions of lives worldwide every year 1 It is either due to cerebral ischemia or hemorrhage and is followed with a series of complex biochemical incidents that leads to the total breakdown of cellular integrity and eventually cell death Accumulative evidence suggests that ischemic strokeinduced neuronal cell death is likely due to excitotoxicity for an excessive stimulation of glutamate receptors 2 3 4 resulting in Ca2+ overloading oxidative radical stress involved in reactive oxygen species ROS/reactive nitrogen species RNS production 2 5 6 7 and suicidal events such as apoptosis and necrosis 5 6 8 9 Blocking the glutamate receptors after ischemic insults has been shown to both be effective 1 and have severe side effects in stroke therapy 10 Therefore glutamate receptors are not desired targets in preventing ischemic neuronal death Spectacular failures in drug development programs and clinical trials for neuroprotective agents have led to the withdrawal of funding aimed at developing new drugs for stroke 1 The direct and effective treatments for stroke remain lacking other than reopening an occluded artery with thrombolytic drugs which makes the identification of new therapeutic targets a matter of great importanceDeathassociated protein kinase 1DAPK1 identified in a screen for genes that influence γinterferon IFNinduced cell death in HeLa cells 11 is a 160kDa Ca2+/calmodulindependent serine/threonine protein kinase 12 whose phosphorylation activity is known to be responsible for certain forms of apoptotic cell death including Fas tumor necrosis factor TNFα 13 ceramide 14 caspase 15 and p53mediated apoptosis 16 as well as in the disruption of matrix survival signals and suppression of integrinmediated cell adhesion 17 In addition DAPK1 which is abundantly expressed in the brain has been linked to neurological diseases associated with neuronal injury and may serve as a target for therapeutic intervention in the treatment of stroke epilepsy and Alzheimer’s disease DAPK1 is of particular interest in stroke to us because of a quantitative proteomic analysis of the deathsignaling proteins that are enrolled to the cytoplasmic tail of the NmethylDaspartate receptor NMDAR during cerebral ischemia revealing DAPK1 as the most prevalent protein 18 Over the past decades several groups have made efforts to decipher DAPK1’s cellular function in stroke focusing on its biochemical properties regulation and especially the target substrates in ischemic injuries It has become apparent that DAPK1 has multiple roles and is linked to several cell deathrelated signaling pathways in ischemia The purposes of this review are to provide a comprehensive overview of the recent literatures on DAPK1 signals in ischemic stroke and to help us better understand the molecular mechanisms of neuronal cell death during stroke injuriesThe identification of myosin light chain MLC as a substrate of DAPK1 facilitated the performance of in vitro DAPK1 kinase assays which enables the analysis of different aspects of its catalytic activity and of its mode of regulation 24 DAPK1 is regulated by a number of mechanisms Firstly the CaMregulatory segment which acts as a pseudosubstrate to the cleft of kinase domain possesses an autoinhibitory effect on the catalytic activity and can be relieved by binding to Ca2+activated CaM 25 and therefore activates DAPK1 Second DAPK1 is negatively regulated by autophosphorylation on serine 308 in the Ca2+/CaM regulatory domain at the basal level Dephosphorylation relieves autoinhibition enhances the interaction between CaM and the DAPK1 CaMregulation segment and stimulates its proapoptotic activities 25 Consistently the mere deletion of this segment from DAPK ΔCaM or the mutation of Ser308 to alanine S308A generates a constitutively active kinaseThe catalytic activity of DAPK1 is controlled by distinct mechanisms First DAPK1 loses catalytic activity upon mutation of Lys42 to Ala K42A 19 one of the amino acids critical to the binding with ATP 26 Second extracellularregulated protein kinase1/2 ERK1/2 binds a docking site within DAPK1’s death domain and phosphorylates DAPK1 Ser735 within the cytoskeletal binding region both in vitro and in vivo stimulating DAPK1 catalytic activity 27 Third the p90 ribosomal S6 kinase RSK a downstream effector of ERK inhibits exogenous DAPK1 cellular activity by phosphorylation of Ser289 within the CaMautoregulatory/binding segment 28 Last but not least DANGER denoted by Damian B et al inhibits DAPK1 activity toward MLC in a concentrationdependent manner without influencing calmodulin’s binding to DAPK1 29 Then how is DAPK1 activated during ischemic stroke It is known that cerebral ischemia induces overexcitation of the NMDA receptor causing excessive Ca2+ flow into the cytoplasm and activates not only CaM but also the calcineurin phosphatase CaN 30 and dephosphorylates DAPK1 in Ser308 Then DAPK1 combines with CaM and becomes activatedIn the developing and adult central nervous system DAPK1 mRNA is widely expressed in proliferative regions within the cerebral cortex and hippocampus 31 32 In addition DAPK1 is critically involved in the processes of both neuronal development and recovery from injury as its activity is increased in response to hypoxic ischemia 24 33 The temporal and spatial pattern of regulation suggests an important role of DAPK1 in neuronal functions The expression of DAPK1 mRNA is increased prior to selective cell death induced by transient forebrain ischemia indicating a close relationship between DAPK1 and neuronal cell death 32 Moreover a small molecule inhibitor of DAPK alkylated 3amino6phenylpyridazine significantly attenuates brain injury after ischemic stroke 34 In addition the activation of DAPK1 has also been implicated in seizureinduced neuronal death 35 36

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