Coordination of JNK1 and JNK2 Is Critical for GADD45α Induction and Its Mediated Cell Apoptosis in Arsenite Responses

Abstract

Arsenite is a well documented environmental pathogen, whereas it has also been applied as medication to treat various neoplasmas. The pathogenic and therapeutic effects of arsenite are associated with cellular apoptotic responses. However, the molecular mechanisms of arsenite-induced apoptosis are not very well understood. Our previous study has shown that arsenite exposure is able to activate JNKs, which subsequently mediate the apoptotic outcome. The present study further revealed that the coordination of JNK1 and JNK2 was critical for the arsenite-induced expression of GADD45␣ (growth arrest and DNA damage 45␣), which in turn mediated the cellular apoptosis. The arsenite-induced apoptosis and GADD45␣ expression were significantly impaired in mouse embryonic fibroblasts deficient in either jnk1 (JNK1 ؊/؊ ) or jnk2 (JNK2 ؊/؊ ). Knockdown of GADD45␣ by its specific small interfering RNA also dramatically reduced the apoptotic responses, and overexpression of GADD45␣ in either JNK1 ؊/؊ or JNK2 ؊/؊ mouse embryonic fibroblasts partially resensitized the cell death. Furthermore, it was found that the regulation of GADD45␣ by JNK1 and JNK2 was achieved through mediating the activation of c-Jun, since in the JNK1 ؊/؊ and JNK2 ؊/؊ cells the c-Jun activation was impaired, and overexpression of the dominant negative mutant of c-Jun (TAM67) in wild type cells could also block GADD45␣ induction as well as cellular apoptosis. Our results demonstrate that the coordination of JNK1 and JNK2 is critical for c-Jun/ GADD45␣-mediated cellular apoptosis induced by arsenite.Arsenite occurs naturally in the earth's crust and is widely distributed in the environment (1). Human exposure to arsenite occurs mainly by ingestion of drinking water contaminated with arsenite from naturally occurring sources or through the inhalation of contaminated dusts in occupational settings (2). As an environmental pathogen, arsenite causes a series of pathophysiological alterations, including immunosuppression and carcinogenesis (3). Paradoxically, arsenite has also been applied as chemotherapeutic reagents to treat various neoplasmas (4). Further insights into the pathogenic and therapeutic effects of arsenite show that it seems to be associated with the apoptotic induction in both normal and tumor cells (5, 6). The inhibition of antiapoptotic Bcl-2 and activation of proapoptotic mitogen-activated protein kinases has recently been shown to participate in the arsenite-induced apoptotic process in various cell models (7-12). These observations suggest that the alternation of the cascades of cellular survival/proapoptotic signaling pathways may be critical for cell apoptotic responses triggered by arsenite. However, the detailed molecular mechanisms still remain to be elucidated.In this study, we applied wild type (WT), 2 JNK1 Ϫ/Ϫ , and JNK2 Ϫ/Ϫ , three immortalized mouse embryonic fibroblasts (MEFs) to evaluate the roles of JNK1 and JNK2 in arseniteinduced apoptosis. It was found that the arsenite-induced apoptosis required both JNK1 and JNK2, since the...

Sensitivity to sodium arsenite in human melanoma cells depends upon susceptibility to arsenite-induced mitotic arrest

“…GADD45 is an arsenite-inducible gene (Chen et al, 2001;Lau et al, 2004) that is involved in cell cycle arrest and has an unresolved role in apoptosis (Sheikh et al, 2000). In addition, recent studies have implicated GADD45 as a key mediator of apoptosis induced by 20 µM arsenite in murine embryonic fibroblasts (Zhang et al, 2006). GADD45 was induced in the SK-Mel-3 and SKMel-28 cell lines under conditions where caspase 3 cleavage was observed ( Figure 8B).…”

“…GADD45 induction by arsenite has been observed with 10 µM arsenite in BEAS-2B cells (Chen et al, 2001) and 20 µM arsenite in rat LEC cells (Lau et al, 2004). Furthermore, Gadd45 induced through c-Jun N-terminal kinase signaling by 20 µM arsenite mediated the initiation of apoptosis in murine embryonic fibroblasts as inferred from impairment of the apoptotic response with Gadd45 knockdown via siRNA (Zhang et al, 2006). In the melanoma cell lines we examined, arsenite induced GADD45 in resistant cell lines only at high concentrations of arsenite or in the presence of BSO or MK571.…”

The Requirement of c-Jun N-terminal Kinase 2 in Regulation of Hypoxia-inducing Factor-1α mRNA Stability

“…After various treatments, the proteins were extracted and total protein was quantified with a Dc protein assay kit (Bio-Rad). Western blotting was carried out as previously described (43). Primary antibody-bound proteins were detected by using an alkaline phosphatase-linked secondary antibody and an ECF Western blotting system (Amersham Biosciences, Piscataway, NJ).…”

A Novel Post-translational Modification of Nucleolin, SUMOylation at Lys-294, Mediates Arsenite-induced Cell Death by Regulating gadd45α mRNA Stability

“…SUMOylation of Nucleolin Increased gadd45␣ mRNA Stability-Growth arrest and DNA damage-inducible gene 45␣ (GADD45␣) is one of the mediators of arsenite-induced apoptosis, as we found previously (47,48); therefore, GADD45␣ induction was investigated to define its involvement in the biological function of SUMO-nucleolin. Consistent with inhibition of the apoptotic response, overexpression of Mn-SOD (Fig.…”