Novel link of anti-apoptotic ATF3 with pro-apoptotic CTMP in the ischemic brain.
Activating transcription factor 3 (ATF3) is a stress-induced transcription factor with diverse functions under disease states in multiple cell types. ATF3 has neuroprotective action against cerebral ischemia, which may involve caspase 3. However, the molecular mechanisms underlying ATF3 regulation of apoptosis are largely unknown. Here, we used gain- and loss-of-function and rescue approaches to demonstrate ATF3 attenuating hypoxic neuronal apoptosis. As well, the protective effect of ATF3 was mediated by downregulation of carboxyl-terminal modulator protein (CTMP), a pro-apoptotic factor that inhibits the anti-apoptotic Akt/PKB cascade. ATF3 (1) downregulated the mRNA and protein levels of CTMP; (2) its temporal expression pattern was reciprocal to that of CTMP; and (3) nuclear localization suggested that ATF3 may regulate CTMP transcription following hypoxic insult. Reporter assays demonstrated that ATF3 suppressed CTMP transcription, whereas ATF3 fusion with VP16, converting ATF3 to transcriptional activator, boosted CTMP transcription. By contrast, NF-κB increased CTMP transcription, and degradation-resistant IκBα decreased CTMP transcription. ChIP assays further confirmed that binding of ATF3 to the ATF/CREB site hindered NF-κB binding to the CTMP promoter, which repressed CTMP expression. Furthermore, CTMP siRNA treatment reduced hypoxic neuronal apoptosis by increasing p-Akt (Ser473) levels and leaving the upstream ATF3 level unchanged. We have identified an endogenous neuroprotective ATF3→CTMP signal cascade that may be a therapeutic target for reducing ischemic brain injury.
Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
Chien-Yu
CY
Huang
Jin-Jer
JJ
Chen
Jui-Sheng
JS
Wu
Hsin-Da
HD
Tsai
Heng
H
Lin
Yu-Ting
YT
Yan
Chung Y
CY
Hsu
Yuan-Soon
YS
Ho
Teng-Nan
TN
Lin
D051700:Activating Transcription Factor 3 / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002545:Brain Ischemia / Q000378:metabolism* / Q000517:prevention & control; D002352:Carrier Proteins / Q000008:administration & dosage / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010170:Palmitoyl-CoA Hydrolase
D051700:Activating Transcription Factor 3; C103002:Atf3 protein, mouse; D002352:Carrier Proteins; C527670:CTMP protein, mouse; D010170:Palmitoyl-CoA Hydrolase