Dysregulation of PAD4-mediated citrullination of nuclear GSK3? activates TGF-? signaling and induces epithelial-to-mesenchymal transition in breast cancer cells.

ABSTRACT: Peptidylarginine deiminase 4 (PAD4) is a Ca(2+)-dependent enzyme that converts arginine and methylarginine residues to citrulline, with histone proteins being among its best-described substrates to date. However, the biological function of this posttranslational modification, either in histones or in nonhistone proteins, is poorly understood. Here, we show that PAD4 recognizes, binds, and citrullinates glycogen synthase kinase-3? (GSK3?), both in vitro and in vivo. Among other functions, GSK3? is a key regulator of transcription factors involved in tumor progression, and its dysregulation has been associated with progression of human cancers. We demonstrate that silencing of PAD4 in breast cancer cells leads to a striking reduction of nuclear GSK3? protein levels, increased TGF-? signaling, induction of epithelial-to-mesenchymal transition, and production of more invasive tumors in xenograft assays. Moreover, in breast cancer patients, reduction of PAD4 and nuclear GSK3? is associated with increased tumor invasiveness. We propose that PAD4-mediated citrullination of GSK3? is a unique posttranslational modification that regulates its nuclear localization and thereby plays a critical role in maintaining an epithelial phenotype. We demonstrate a dynamic and previously unappreciated interplay between histone-modifying enzymes, citrullination of nonhistone proteins, and epithelial-to-mesenchymal transition.

SUBMITTER: Stadler SC 

PROVIDER: S-EPMC3718105 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature