AIP1 recruits phosphatase PP2A to ASK1 in tumor necrosis factor-induced ASK1-JNK activation.
Previously we have shown that AIP1 (apoptosis signal-regulating kinase [ASK]1-interacting protein 1), a novel member of the Ras-GAP protein family, facilitates dephosphorylation of ASK1 at pSer967 and subsequently 14-3-3 release from ASK1, leading to enhanced ASK1-JNK signaling. However, the phosphatase(s) responsible for ASK1 dephosphorylation at pSer967 has not been identified. In the present study, we identified protein phosphatase (PP)2A as a potential phosphatase in vascular endothelial cells (ECs). Tumor necrosis factor (TNF)-induced dephosphorylation of ASK1 pSer967 in ECs was blocked by PP2A inhibitor okadaic acid. Overexpression of PP2A catalytic subunit induced dephosphorylation of ASK1 pSer967 and activation of c-Jun N-terminal kinase (JNK). In contrast, a catalytic inactive form of PP2A or PP2A small interfering RNA blunted TNF-induced dephosphorylation of ASK1 pSer967 and activation of JNK without effects on NF-kappaB activation. Whereas AIP1, via its C2 domain, binds to ASK1, PP2A binds to the GAP domain of AIP1. Endogenous AIP1-PP2A complex can be detected in the resting state, and TNF induces a complex formation of AIP1-PP2A with ASK1. Furthermore, TNF-induced association of PP2A with ASK1 was diminished in AIP1-knockdown ECs, suggesting a critical role of AIP1 in recruiting PP2A to ASK1. TNF-signaling molecules TRAF2 and RIP1, known to be in complex with AIP1 and activate AIP1 by phosphorylating AIP1 at Ser604, are critical for TNF-induced ASK1 dephosphorylation. Finally, PP2A and AIP1 cooperatively induce activation of ASK1-JNK signaling and EC apoptosis, as demonstrated by both overexpression and small interfering RNA knockdown approaches. Taken together, our data support a critical role of PP2A-AIP1 complex in TNF-induced activation of ASK1-JNK apoptotic signaling.
Min
Wang
W
Vascular Biology and Therapeutics Program and Department of Pathology, Yale University School of Medicine, 10 Amistad St, New Haven, CT 06520, USA. wang.min@yale.edu
Lin
Yan
Y
Tang
Shibo
S
Yu
Luyang
L
Zhang
Haifeng
H
Wan
Ting
T
Luhn
Tricia
T
Fu
Haian
H
Chen
Hong
H
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001011:Aorta / Q000378:metabolism / Q000473:pathology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins; D002417:Cattle; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000473:pathology; D051528:Guanylate Kinases; D006801:Humans; D048670:MAP Kinase Kinase 4 / Q000378:metabolism*; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D011506:Proteins; D014409:Tumor Necrosis Factor-alpha; D048848:MAP Kinase Kinase Kinase 5; C482858:MAP3K5 protein, human; D048670:MAP Kinase Kinase 4; D051528:Guanylate Kinases; C485777:MAGI2 protein, human; D054648:Protein Phosphatase 2