Cdc25A promotes cell survival by stimulating NF-κB activity through IκB-α phosphorylation and destabilization

Abstract

Cell division cycle 25A (Cdc25A), a dual specificity protein phosphatase, exhibits anti-apoptotic activity, but the underlying molecular mechanisms are poorly characterized. Here we report that Cdc25A inhibits cisplatin-induced apoptotic cell death by stimulating nuclear factor-kappa B (NF-κB) activity. In HEK-293 cells, Cdc25A decreased protein level of inhibitor subunit kappa B alpha (Iκ-Bα) in association with increased serine 32-phosphorylation, followed by stimulation of transcriptional activity of NF-κB. Inhibition of NF-κB activity by chemical inhibitor or overexpression of Iκ-Bα in Cdc25A-elevated cancer cells resistant to cisplatin improved their sensitivity to cisplatin-induced apoptosis. Our data show for the first time that Cdc25A has an important physiological role in NF-κB activity regulation and it may be an important survival mechanism of cancer cells.

Introduction

Cdc25A is a member of cell division cycle 25 (Cdc25) family of protein with highly conserved dual-specific phosphatase activity [1], [2]. It plays a key role in G1/S phase transition during normal cell division through the activation of cyclin E/cyclin-dependent kinase2 (CDK2) complex [3] and in the G2/M checkpoint mechanisms activated in response to DNA damage [4], [5]. Therefore, dysregulation of Cdc25A levels results in checkpoint bypass and genomic instability. Indeed, Cdc25A overexpression has been reported in many high-grade tumors [6], [7], [8] and often correlates with poor progression in human cancers. Cdc25A overexpression also critically contributes to the resistance of tumor cells to chemotherapy-mediated cell death [9]. However, the underlying molecular mechanisms remain to be elucidated.

The nuclear factor κB (NF-κB) is a family of transcription factors that regulates the expression of various genes involved in cell survival signaling [10], [11]. The prototypical and ubiquitously expressed NF-κB complex is the p50/p65 heterodimer, of which RelA or p65 subunit directly regulate expression of Bcl-2 and IAP family survival proteins [12], [13]. In the classical pathway, NF-κB remains in cytosol in an inactive state, complexed with inhibitor subunit kappa B (IκB). Under activation stimulus, IκB is phosphorylated by IκB kinases, IKKα and IKKβ, which is subsequently ubiquitinated and degraded by the 26S proteasome, thus leading to the nuclear translocation and transcriptional activation of NF-κB [14]. In the present study, we demonstrate that Cdc25A stimulates NF-κB activity by destabilizing IκB protein through inducing its phosphorylation and ubiquitination. Our study supports a novel function of Cdc25A as a positive regulator of NF-κB.