Ataxia-Telangiectasia, Mutated (ATM)/Nuclear Factor κ Light Chain Enhancer of Activated B Cells (NFκB) Signaling Controls Basal and DNA Damage-induced Transglutaminase 2 Expression

Abstract

Transglutaminase 2 (TG2) is a ubiquitously expressed enzyme that cross-links proteins and its overexpression, linked to a drug resistant phenotype, is commonly observed in cancer cells. Further, up-regulation of TG2 expression occurs during response to various forms of cell stress; however, the molecular mechanisms that drive inducible expression of the TG2 gene (TGM2) require elucidation. Here we show that genotoxic stress induces TG2 expression through the Ataxia-Telangiectasia, Mutated (ATM)/Nuclear Factor κ light chain enhancer of activated B cells (NFκB) signaling pathway. We further document that NFκB is both necessary and sufficient to drive constitutive TG2 expression in cultured cell lines. Additionally, shRNA-mediated knockdown or pharmacological inhibition of the ATM kinase results in reduced constitutive TG2 expression and NFκB transcriptional activity. We document that the NFκB subunit p65 (RelA) interacts with two independent consensus NFκB binding sites within the TGM2 promoter, that mutation of either site or pharmacological inhibition of NFκB reduces TGM2 promoter activity, and genotoxic stress drives heightened association of p65 with the TGM2 promoter. Finally, we observed that knockdown of either p65 or ATM in MDA-MB-468 breast cancer cells expressing recombinant TG2 partially reduces resistance to doxorubicin, indicating that the drug resistance linked to overexpression of TG2 functions, in part, through p65 and ATM. This work establishes a novel ATM-dependent signaling loop where TG2 and NFκB activate each other resulting in sustained activation of NFκB and acquisition of a drug-resistant phenotype.