Heat Shock Protein Hsp72 Is a Negative Regulator of Apoptosis Signal-Regulating Kinase 1

Abstract

Heat shock protein 72 (Hsp72) is thought to protect cells against cellular stress. The protective role of Hsp72 was investigated by determining the effect of this protein on the stress-activated protein kinase signaling pathways. Prior exposure of NIH 3T3 cells to mild heat shock (43°C for 20 min) resulted in inhibition of H 2 O 2 -induced activation of apoptosis signal-regulating kinase 1 (ASK1). Overexpression of Hsp72 also inhibited H 2 O 2 -induced activation of ASK1 as well as that of downstream kinases in the p38 mitogen-activated protein kinase (MAPK) signaling cascade. Recombinant Hsp72 bound directly to ASK1 and inhibited ASK1 activity in vitro. Furthermore, coimmunoprecipitation analysis revealed a physical interaction between endogenous Hsp72 and ASK1 in NIH 3T3 cells exposed to mild heat shock. Hsp72 blocked both the homooligomerization of ASK1 and ASK1-dependent apoptosis. Hsp72 antisense oligonucleotides prevented the inhibitory effects of mild heat shock on H 2 O 2 -induced ASK1 activation and apoptosis. These observations suggest that Hsp72 functions as an endogenous inhibitor of ASK1.Apoptosis signal-regulating kinase 1 (ASK1) is a widely expressed serine-threonine kinase that was initially discovered as a mitogen-activated protein kinase kinase kinase (MAPKKK) in the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and p38 MAPK signaling cascades (12, 13). ASK1 functions in apoptosis induced by diverse stimuli, including tumor necrosis factor alpha (TNF-␣), Fas, and many apoptotic stresses (12,13,30). Overexpression of a dominantnegative mutant of ASK1 thus prevents apoptosis induced by withdrawal of growth factors, DNA-damaging agents, TNF-␣, or agonistic antibodies to Fas (4,13,16,30). Activation of ASK1 is reported to induce apoptotic cell death by triggering mitochondrial events that include the release of cytochrome c from mitochondria and the subsequent activation of caspase 9 and caspase 3 (11).Many cellular stresses that stimulate the stress-activated MAPK pathways can also induce expression of heat shock proteins. Heat shock protein 72 (Hsp72) is the major inducible heat shock protein (35). It plays a role in many cellular activities including protein synthesis, folding, and translocation into organelles as well as the assembly of multiprotein complexes (2,5,24,25,33). Hsp72 contains two conserved domains, an ATP-binding domain (ABD) and a peptide-binding domain (PBD), that are important for its chaperon function (7, 21). Hsp72 also prevents cell death initiated by various apoptotic stresses including heat shock, ceramide, ionizing irradiation, TNF-␣, and ischemia (8,14,20,23,32). Hsp72 suppresses several apoptotic signaling pathways, including caspase cascades and stress-activated MAPK pathways that include the JNK and p38 signaling cascades (3,8,9,15,17,19,22,23,29,31). Furthermore, Hsp72 has been shown to physically interact with and inhibit Apaf-1 and apoptosis-inducing factor, resulting in suppression of caspase-dependent and -independent apoptosis, respectively ...

CIB1 functions as a Ca 2+ -sensitive modulator of stress-induced signaling by targeting ASK1

“…ASK1 plays a role in apoptosis induced by a variety of cellular stressors including oxidative stress, tumor necrosis factor (TNF)-␣, endoplasmic reticulum stress, and anticancer drugs (4). ASK1-mediated signaling is modulated either positively or negatively by various ASK1 binding proteins that include thioredoxin and tumor necrosis factor receptor-associated factors 2 (TRAF2) (5)(6)(7)(8)(9)(10).…”

Small Heat-Shock Protein Hsp20 Attenuates β-Agonist–Mediated Cardiac Remodeling Through Apoptosis Signal–Regulating Kinase 1

“…32 Furthermore, Hsp72 physically associates with ASK1, thereby inhibiting H 2 O 2 -induced activation of ASK1 in NIH 3T3 cells. 33 Hsp90 also forms a complex with ASK1 to retain ASK1 in an inactive state and protects endothelial cells from H 2 O 2 -induced apoptosis. 34 Thus, various regulators may act via different mechanisms to block the activity of ASK1.…”

Human glutathione S-transferase P1-1 interacts with TRAF2 and regulates TRAF2–ASK1 signals

“…TNF-a or TRAF2 overexpression stimulates production of reactive oxygen species (ROS) that in turn activates ASK1-MKKs-JNK/p38 signal pathways through eliciting TRAF2-ASK1 interaction in target cells Hoeflich et al, 1999;Liu et al, 2000;Tobiume et al, 2002). Some redoxsensing proteins including thioredoxin (Trx), heat-shock protein 72 (HSP72) and 90 (HSP90) and glutathione S-transferase (GST) Mu (GSTM1-1) Cho et al, 2001;Park et al, 2002;Zhang et al, 2005) could bind ASK1 and inhibit its activity. TRAF2-induced ASK1 activation is likely to be owing to prior dissociation of Trx, a major endogenous inhibitor of ASK1, from ASK1.…”