Inhibition of protein kinase C βII downregulates tristetraprolin expression in activated macrophages

Abstract

Tristetraprolin (TTP) is a 3'-UTR-binding protein known to destabilize mRNAs of TNFalpha and some other cytokines and to act as an anti-inflammatory factor. The aim of this study was to investigate the role of classical protein kinase C isoenzymes (cPKC) in the regulation of TTP expression in activated macrophages. The expression of TTP in J774 macrophages was induced by a combination of LPS and phorbol myristate acetate (PMA). The effects of cPKC inhibitors and the effects of cPKC activation and downregulation by PMA on TTP protein and mRNA expression were determined by Western blotting and quantitative RT-PCR, respectively. Also, the effect of PKC beta II inhibitor CGP53353 on the activation of transcription factors AP-2, NF-kappaB, EGR1 and Sp1 was assessed. cPKC inhibitors RO318220, GO6976, LY333531 and CGP53353 inhibited LPS and PMA-induced expression of TTP protein and mRNA. Similar effects were obtained when cPKC isoenzymes were downregulated by PMA. In addition, CGP53353 decreased the activation of transcription factor AP-2. The results suggest that cPKCs, most likely PKC beta II, upregulate TTP expression in activated macrophages. This regulation is possibly mediated through the activation of transcription factor AP-2, and serves as an additional mechanism how PKC beta regulates the inflammatory process.