Signalling to translational activation of tumour necrosis factor-alpha expression in human THP-1 cells

Monocytic THP-1 cells expressed tumour necrosis factor-alpha (TNF-alpha) mR NA, but hardly any detectable TNF-alpha protein and a partially activated M AP kinase ERK-2 in the unstimulated state. Stimulation with phorbol ester l ed to expression of TNF-alpha protein without significant changes in mRNA, a response that was sensitive to the MEK-1/2 inhibitors PD98059 and U0126. A calcium signal also led to expression of TNF-alpha protein, but now accom panied by a rapid increase in mRNA, A synergistic effect between phorbol es ter and calcium ionophore was evident at the level of TNF-alpha protein, bu t not its mRNA. Stimulation with anisomycin led to a TNF-alpha expression t hat was sensitive to the p38 inhibitor SB203580, Actinomycin D lowered TNF- alpha mRNA in a similar way as PD98059 but was less inhibitory on PMA- or a nisomycin-induced formation of TNF-alpha, thus confirming that these agents acted by causing translational derepression, Thus, in THP-1 cells MAP kina se pathways involving MEK-1/2 and possibly ERK-2 as well as the human p38 a nalogue mere essential for basal TNF-a mRNA expression and translational ac tivation. (C) 2000 Academic Press.