gadd45 Is Not Required for Activation of c-Jun N-terminal Kinase or p38 during Acute Stress

Abstract

Cells respond to environmental stress with activation of c-Jun N-terminal kinase (JNK) and p38. Recent studies have implicated Gadd45 and two related proteins, MyD118/Gadd45␤ and CR6/Gadd45␥, as initiators of JNK/p38 signaling via their interaction with an upstream kinase MTK1. It was proposed that stress-induced expression of the Gadd45-related proteins leads to MTK1 activation and subsequent JNK/p38 activation. Using embryo fibroblasts from gadd45-null mice, we have addressed the requirement for Gadd45 in mediating JNK/p38 activation during acute stress. Comparison of JNK/p38 activities in response to methyl methanesulfonate, hydrogen peroxide, UVC irradiation, sorbitol, and anisomycin treatment of gadd45 ؉/؉ and gadd45fibroblasts revealed no deficiency in JNK/p38 activation in gadd45 ؊/؊ fibroblasts. In addition, in wild type cells, JNK and p38 activation significantly preceded gadd45 induction with all stresses. Examination of myd118/ gadd45␤ and cr6/gadd45␥ expression in gadd45 ؉/؉ and gadd45 ؊/؊ fibroblasts revealed similar induction patterns in the two cell types, which, like gadd45 expression, was delayed relative to JNK/p38 activation. We conclude that gadd45 expression is not required for activation of JNK/p38 by environmental stresses, nor are stress-induced increases in myd118/gadd45␤ and cr6/ gadd45␥ expression necessary for kinase activation in response to such insults.gadd45 (also referred to as gadd45␣) was first described by Fornace et al. (1,2) as showing increased expression in response to DNA-damaging agents and other stresses associated with growth arrest. Although its precise function remains unclear, Gadd45 has been implicated in a variety of growth regulatory mechanisms, including DNA replication, DNA repair, G 2 /M checkpoint control, and apoptosis (3-8). Indeed, Gadd45 has been shown to bind to several proteins involved in these processes, including proliferating cell nuclear antigen (4), p21Waf1/Cip1 (5), and Cdc2 (7). Two other genes with homology to gadd45 have also been described: myd118 (also referred to as gadd45␤) (9), implicated in myeloid differentiation, and the recently described gadd45␥ (also referred to as cr6) (10, 11).The mitogen-activated protein kinase (MAPK) 1 signaling cascades leading to the activation of c-Jun N-terminal kinase (JNK) and p38 play important roles in mediating cellular responses to stressful stimuli (reviewed in Refs. 12-14). JNK and p38 are phosphorylated via a group of related kinases (MAPKK), which are in turn activated by another set of kinases, designated MAPKKK. While some of the upstream kinases involved in JNK and p38 activation are selective for one or the other pathway, others function in the activation of both signaling cascades. The human MAPKKK MTK1 (its mouse homologue is referred to as MEKK4) has been implicated in the activation of both JNK and p38 (15, 16). Using a yeast twohybrid screen to detect proteins that interact with MTK1, Takekawa and Saito (10) recently identified the Gadd45-related proteins as MTK1-binding proteins. Additio...

Signaling pathways involved in induction of GADD45 gene expression and apoptosis by troglitazone in human MCF-7 breast carcinoma cells

“…with assays in triplicate Troglitazone induces GADD45 in breast cancer cells F Yin et al terminal autoinhibitory domain which permits recognition and phosphorylation of MKK6 and SEK1 that, in turn, directly activates p38 MAPK and JNK (Mita et al, 2002). Another study, however, found that GADD45 null cells activated JNK to a similar extent as GADD45 þ / þ cells, after exposure to ultraviolet light and hydrogen peroxide (Wang et al, 1999). Thus, unmasking of the MEKK4 kinase domain by protein-protein interaction with GADD45 may represent just one of many mechanisms resulting in p38 and JNK MAPKs activation by stress signals.…”

Myeloid differentiation (MyD) primary response genes in hematopoiesis

“…Distinct expression patterns for these genes were observed also in a variety of murine tissues (Zhang et al, 1999). Importantly, individual members of the GADD45 gene family are dierentially induced by a variety of genetic and environmental stress agents; this suggests that each gene is induced by a distinct subset of environmental stresses (Shaulian Oncogene MyD/Gadd as therapeutic targets DA Liebermann and B Hoffman and Karin, 1999;Takekawa and Saito 1998;Wang et al, 1999a;Zhang et al, 1999Zhang et al, , 2001Zhang, 2000). Short term transfection assays have revealed that MyD118/CR6/GADD45 synergize to suppress colony formation of several human tumor cell lines Zhang et al, 1999).…”

“…GADD45 proteins also interact with and activate the stress-responsive MTK1/MEKK4 kinase, which is an upstream activator of the p38/JNK kinase pathways implicated in environmental stress induced apoptosis (Takekawa and Saito, 1998). However, the signi®cance of GADD45 interactions with MEKK4 in activation of the stress responsive JNK/p38 apoptotic pathways is still undetermined (Shaulian and Karin, 1999;Wang et al, 1999a). Recently it has been suggested that GADD45b and GADD45g activation of JNK/p38 plays an essential role in cytokine induced (innate) IFNg production by TH-1 thymocytes (Lu et al, 2001;Yang et al, 2001).…”

Myeloid Differentiation (MyD)/Growth Arrest DNA Damage (GADD) genes in tumor suppression, immunity and inflammation

“…12 Importantly, individual members of the GADD45 gene family are differentially induced by a variety of genetic and environmental stress agents; this suggests that each gene is induced by a distinct subset of environmental stresses. [12][13][14][15]192,193 Short-term transfection assays have revealed that MyD118/CR6/ GADD45 synergize to suppress colony formation of several human tumor cell lines. 10,12 To what extent the function of each of the MyD118/CR6/GADD45 proteins is unique or overlaps with the functions of the other proteins, remains to be determined.…”

“…15 However, the significance of GADD45 interactions with MEKK4 in activation of the stressresponsive JNK/p38 apoptotic pathways is still undetermined. 192,193 Recently it has been suggested that GADD45␤ and GADD45␥ activation of JNK/p38 plays an essential role in cytokine-induced (innate) IFN␥ production by TH-1 thymocytes (Figure 3). 222,223 Finally GADD45 proteins are also capable of homo-and hetero-interactions among themselves (Ref.…”