GADD45γ regulates TNF-α and IL-6 synthesis in THP-1 cells

This study investigated the link between growth arrest and DNA damage 45 gamma (GADD45 gamma) expression and tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) synthesis. We stimulated THP-1 monocyte cells using lipopolysaccharide (LPS). We knocked-down and over-expressed GADD45 gamma using lentiviral vectors harboring GADD45 gamma short hairpin RNA and GADD45 gamma open reading frame, respectively. To inhibit activation of c-Jun-terminal kinase (JNK), we used a specific inhibitor, SP600125. LPS stimulation of THP-1 cells resulted in increased expression of GADD45 gamma mRNA which reached its peak 2 h after stimulation and gradually diminished thereafter. TNF-alpha and IL-6 were up-regulated at both the mRNA and protein levels in activated THP-1 cells. Knock-down of GADD45 gamma reduced TNF-alpha protein production by up to 75 % and IL-6 protein by up to 60 %. In contrast, over-expression of GADD45 gamma increased TNF-alpha production by six-fold and IL-6 protein by 80-fold. There was a discrepancy between TNF-alpha mRNA and its protein level, whereas IL-6 mRNA and its protein level were correlated. Knock-down of GADD45 gamma decreased the JNK activity, suggesting that JNK may play the role of a downstream mediator for the pro-inflammatory effects of GADD45 gamma. We show evidence that GADD45 gamma may regulate TNF-alpha and IL-6 expression in activated THP-1 monocyte cells.