Gadd45a Expression Induces Bim Dissociation from the Cytoskeleton and Translocation to Mitochondria

Abstract

Gadd45a, a p53-and BRCA1-regulated stress protein, has been implicated in the maintenance of genomic fidelity, probably through its roles in the control of cell cycle checkpoint and apoptosis. However, the mechanism(s) by which Gadd45a is involved in the induction of apoptosis remains unclear. We show here that inducible expression of Gadd45a protein causes dissociation of Bim, a Bcl2 family member, from microtubuleassociated components and translocation to mitochondria. The Bim accumulation in mitochondria enhances interaction of Bim with Bcl-2, relieves Bax from Bcl-2-bound complexes, and subsequently results in release of cytochrome c into the cytoplasm. Suppression of endogenous Bim greatly inhibits Gadd45a induction of apoptosis. Interestingly, Gadd45a interacts with elongation factor 1␣ (EF-1␣), a microtubule-severing protein that plays an important role in maintaining cytoskeletal stability, and inhibits EF-1␣-mediated microtubule bundling, indicating that the interaction of Gadd45a with EF-1␣ disrupts cytoskeletal stability. A mutant form of Gadd45a harboring a deletion of EF-1␣-binding domain fails to inhibit microtubule stability and to induce Bim translocation to mitochondria. Furthermore, coexpression of EF-1␣ antagonizes Gadd45a's property of suppressing cell growth and inducing apoptosis. These findings identify a novel link that connects stress protein Gadd45a to the apoptotic machinery and address the importance of cytoskeletal stability in apoptotic response to DNA damage.

A dual role of p21waf1/cip1 gene in apoptosis of HEp-2 treated with cisplatin or methotrexate

“…This speculation could be substantiated by a recent finding showing that Bim, also being a BH3-only protein, triggers p53-independent apoptotic pathways, whereby it could be activated through cytoskeletal sequestration. 46 For example, inducible expression of GADD45a in HeLa cells resulted in growth suppression and apoptosis causing destabilization of the cytoskeleton and translocation of Bim into mitochondria. 46 It seems that similar phenomenon observed in our study led to decreased levels of DFFB transcripts in the combined treatment with methotrexate and AdCMV-p21.…”

BCL-2 family regulation by the 20S proteasome inhibitor bortezomib

“…Dissociation from LC8 is a caspase-independent event and is driven by JNK phosphorylation (Lei and Davis, 2003) that leads to translocation of BIM, interaction and activation of BAX/BAK. The p53 and the BRCA1 transcriptionally regulated protein GADD45a mediates apoptosis by dissociating BIM from the cytoskeleton via an interaction with the microtubule-severing protein EF1-a (Tong et al, 2005). Microtubule damaging agents such as paclitaxel require BIM to induce apoptosis (Sunters et al, 2003;Anderson, 2005;Annis et al, 2005), as is the case for glucocorticoids (Ling et al, 2003a;Abrams et al, 2004;Zhang and Insel, 2004).…”

Gadd45a inhibits cell migration and invasion by altering the global RNA expression

“…8 In addition, it can induce apoptosis by promoting Bim translocation to mitochondria. 9 Most recently, controversial roles of Gadd45a in the control of DNA demethylation have been reported. 10,11 As a tumor-suppressor gene, Gadd45a negatively regulates cell malignancy.…”