Abstract
The apoptosis signal-regulating kinase 1 (ASK1)-JNK/p38 signaling pathway is pivotal component in cell apoptosis and can be activated by a variety of death stimuli including tumor necrosis factor (TNF) alpha and oxidative stress (reactive oxygen species). However, the mechanism for ASK1 activation is not fully understood. We have recently identified ASK1-interacting protein (AIP1) as novel signal transducer in TNFalpha-induced ASK1 activation by facilitating dissociation of ASK1 from its inhibitor 14-3-3. In the present study, we employed yeast two-hybrid system using the N-terminal domain of AIP1 as bait and identified homeodomain-interacting protein kinase 1 (HIPK1) as an AIP1-associated protein. Interestingly, we showed that TNFalpha induced HIPK1 desumoylation concomitant with a translocation from nucleus to cytoplasm at 15 min followed by a return to nucleus by 60 min. The kinetics of HIPK1 translocation correlates with those of stress-induced ASK1-JNK/P38 activation. A specific JNK inhibitor blocked the reverse but not the initial translocation of HIPK1, suggesting that the initial translocation is an upstream event of ASK1-JNK/p38 signaling and JNK activation regulates the reverse translocation as a feedback mechanism. Consistently, expression of HIPK1 increased, whereas expression of a kinase-inactive form (HIPK1-D315N) or small interference RNA of HIPK1 decreased stress-induced ASK1-JNK/P38 activation without effects on IKK-NF-kappaB signaling. Moreover, a sumoylation-defective mutant of HIPK1 (KR5) localizes to the cytoplasm and is constitutively active in ASK1-JNK/P38 activation. Furthermore, HIPK1-KR5 induces dissociation of ASK1 from its inhibitors 14-3-3 and thioredoxin and synergizes with AIP1 to induce ASK1 activation. Our study suggests that TNFalpha-induced desumoylation and cytoplasmic translocation of HIPK1 are critical in TNFalpha-induced ASK1-JNK/p38 activation.
Highlights
Apoptosis signal-regulating kinase 1 (ASK1),1 a member of the mitogen-activated protein kinase kinase kinase family, is an upstream activator of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase signaling cascades [1]
homeodomaininteracting protein kinase 1 (HIPK1) Is Translocated from Nucleus to Cytoplasm in Response to tumor necrosis factor (TNF)␣—We have recently identified a novel Ras-GAP as an apoptosis signal-regulating kinase 1 (ASK1)-interacting protein (AIP1, called DAB2-interactin protein)
In response to TNF␣, AIP1 binds to ASK1 and facilitates 14-3-3 dissociation from ASK1 leading to ASK1-JNK activation [17]
Summary
Apoptosis signal-regulating kinase 1 (ASK1), a member of the mitogen-activated protein kinase kinase kinase family, is an upstream activator of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase signaling cascades [1]. ASK1 activation appears to involve several sequential steps including release of cellular inhibitors such as Trx, glutaredoxin, glutathione S-transferase Mu, heat shock proteins, and 14-3-3; ASK1 oligomerization/ autophosphorylation at Thr-845; and scaffold protein-mediated association of ASK1 with downstream MKK and JNK. We have recently identified a novel ASK1-interacting protein (AIP1) that plays a critical role in 14-3-3 release and ASK1-JNK activation by TNF␣/ROS [17]. AIP1, a new member of Ras-GAP protein family, via its protein kinase C-conserved (C2) domain binds to a sequence surrounding the 14-3-3-binding site (Ser(P)-967) on ASK1 but preferentially to a dephosphorylated active form of ASK1. Further studies indicate that HIPK2 phosphorylates p53 on Ser, resulting in activation of p53-dependent transcription, cell growth regulation, and apoptosis initiation [29, 30]. This raises the possibility that HIPK translocation from nucleus to cytoplasm is involved in TNF␣/ Fas signaling
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
