Activation of the p38 Signaling Pathway by Heat Shock Involves the Dissociation of Glutathione S-Transferase Mu from Ask1

Abstract

Despite the importance of the stress-activated protein kinase pathways in cell death and survival, it is unclear how stressful stimuli lead to their activation. In the case of heat shock, the existence of a specific mechanism of activation has been evidenced, but the molecular nature of this pathway is undefined. Here, we found that Ask1 (apoptosis signal-regulating kinase 1), an upstream activator of the stress-activated protein kinase p38 during exposure to oxidative stress and other stressful stimuli, was also activated by heat shock. Ask1 activity was required for p38 activation since overexpression of a kinase dead mutant of Ask1, Ask1(K709M), inhibited heat shock-induced p38 activation. The activation of Ask1 by oxidative stress involves the oxidation of thioredoxin, an endogenous inhibitor of Ask1. A different activation mechanism takes place during heat shock. In contrast to p38 induction by H 2 O 2 , induction by heat shock was not antagonized by pretreatment with the antioxidant Nacetyl-L-cysteine or by overexpressing thioredoxin and was not accompanied by the dissociation of thioredoxin from Ask1. Instead, heat shock caused the dissociation of glutathione S-transferase Mu1-1 (GSTM1-1) from Ask1 and overexpression of GSTM1-1-inhibited induction of p38 by heat shock. We concluded that because of an alternative regulation by the two distinct repressors thioredoxin and GSTM1-1, Ask1 constitutes the converging point of the heat shock and oxidative stress-sensing pathways that lead to p38 activation.Heat shock affects all proteins and structures but nevertheless produces a highly specific stress response aimed at protecting the cells and re-establishing homeostasis. In addition to the well characterized transcriptional activation of the genes coding for heat shock proteins (1-3), within minutes heat shock activates a major signal transduction pathway involving the stress-activated protein kinase p38 and leading to the phosphorylation of heat shock protein 27 (HSP27) (4, 5). Phosphorylation of HSP27 activates a protective function, which may result from the known phosphorylation-modulated function of the protein at the level of the actin microfilaments (6 -8) or from other described protective activities, either as a chaperone (9 -11) or as an inhibitor of apoptotic processes (12)(13)(14). Activation of the p38 pathway and phosphorylation of HSP27 occurs within minutes at elevated temperature and constitutes a very tightly regulated response (15). After a mild heat shock, cells becomes refractory to reinduction of p38 activity by a second heat shock but remained fully responsive to reinduction by other stresses, cytokines, or growth factors (15). The specificity of this desensitization reinforces the existence of a highly specific heat shock-sensing pathway upstream of p38. Despite its importance for cell survival, the signaling components and the molecular mechanism leading to heat shock-induced p38 activation are unknown.Little is known about the mechanisms of activation of the stress-sensitive pathways. I...

Glutathione S-transferase polymorphisms: cancer incidence and therapy

“…Under normal conditions, ASK1 exhibits low activity because of its sequestration via GSTM1. This protein:protein interaction forms a GSTM1:ASK1 complex, which is dissociated under stressful conditions leading to the release and activation of ASK1 (Figure 2) (Saitoh et al, 1998;Dorion et al, 2002). This mechanism is similar to the one proposed for GSTp:JNK.…”

“…This mechanism is similar to the one proposed for GSTp:JNK. In conditions such as oxidative stress or heat shock, GSTM1 oligomerizes allowing for the release of ASK1 and subsequent induction of apoptosis (Dorion et al, 2002). Impaired clinical response to therapy in a variety of tumor types has been associated with an altered expression of GSTM1.…”

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

“…GSTP1-1 functions as an endogenous inhibitor of JNK, which interact with the C-terminal of that kinase (Adler et al, 1999;Yin et al, 2000;Wang et al, 2001). GSTM1-1 (GSTm), another member of GST superfamily, has been identified as a negative regulator of ASK1 and MEKK1 (Cho et al, 2001;Dorion et al, 2002;Ryoo et al, 2004). Our previous study also showed that GSTP1-1 repressed ROS-induced ASK1 activation in a dose-dependent manner (Yin et al, 2001).…”

p38α limits the contribution of MAP17 to cancer progression in breast tumors

“…ASK1 activation may involve oligomerization and autophosphorylation. In unstressed cells, this activation is prevented by the binding of proteins, such as thioredoxin and Gstm1, which are sensitive to stress and dissociate from ASK1 after oxidative stress and heat shock, respectively (Dorion et al, 2002;Matsukawa et al, 2004).…”

“…MAP17 oncogenic abilities would only be reflected in cell lines that have acquired the ability to uncouple p38a activation from oxidative stress production, resulting in enhanced tumorigenicity. In many cases, this mechanism relies on the ability of the GST family members Gstm1 and Gstm2 to impair p38a activation in response to ROS accumulation (Dorion et al, 2002).…”