Regulation of Btg2/TIS21/PC3 expression via reactive oxygen species-protein kinase C-NFκB pathway under stress conditions

Human B-cell translocation gene 2 (BTG2), an ortholog of mouse TIS21 (12-O-tetradecanoyl phorbol-13-acetate inducible sequence 21) and rat PO (Pheochromocytoma Cell 3), is a tumor suppressor gene that belongs to an antiproliferative gene family. Btg2 is involved in a variety of biological processes including cell growth, development, differentiation, senescence, and cell death and its expression is strongly regulated by p53. Recently, we have reported transient induction of Btg2 expression in response to oxidative damage; however, the regulatory mechanism was not explored. In the present study we revealed NF kappa B as the upstream mediator involved in Btg2 transcription in response to cell stress challenges such as serum deprivation and oxidative stress i.e. H2O2, TPA or doxorubicin treatments in several cell lines. We observed close interrelation between generation of reactive oxygen species (ROS), enhanced I kappa B alpha degradation, nuclear translocation of NF kappa B (p65/RelA) and the significant increase of Btg2 expression independent of p53 status. ChIP analysis revealed an enrichment of RelA (p65) bound to the kappa B response element on Btg2 promoter in response to the cell stress challenges. Employing various inhibitors led to cytoplasmic accumulation of I kappa B alpha, decreased p65 nuclear translocation along with significant reduction of Btg2 expression. Generation of ROS was the common event mediating NF kappa B activation and Btg2 transcription. Furthermore. PKC activation was also found to be a critical factor mediating ROS-mediated signals to NF kappa B pathway that culminate on Btg2 regulation, and specifically PKC-delta was responsible for this regulation under oxidative stress. However, serum deprivation-associated ROS generation bypassed PKC activation for induction of Btg2 expression via NF kappa B activation. The present data imply that oxidative stresss upregulates Btg2 expression via ROS-PKC-NF kappa B cascade, independent of p53 status that in turn could be involved in mediating various biological phenotypes depending on the cellular context. (C) 2013 Elsevier Inc. All rights reserved.