Involvement of p38 mitogen-activated protein kinase in heat shock protein 27 induction in human neutrophils

Abstract

We investigated whether tumor necrosis factor-α (TNF-α) stimulates the induction of heat shock protein 27 (HSP27) in human neutrophils and the mechanism underlying this induction. In intact neutrophils, almost no HSP27 was detected. Stimulation of neutrophils by TNF-α increased the levels of HSP27 in the presence, but not in the absence, of cycloheximide. Reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that TNF-α also induced HSP27 mRNA in the presence of cycloheximide. TNF-α induced the phosphorylation of p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase. The HSP27 accumulation induced by TNF-α was significantly suppressed by 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1 H-imidazole (SB203580) or 4-(4-fluorophenyl)-2-(4-nitrophenyl)-5-(4-pyridyl)-1 H-imidazole (PD169316); both are specific inhibitors of p38 MAP kinase, but not by 2′-amino-3′-methoxyflavone (PD098059, a specific inhibitor of the upstream kinase that activates p44/p42 MAP kinase). The accumulation of HSP27 induced by TNF-α plus cycloheximide was also suppressed by pretreatment with a specific protein kinase C (PKC) inhibitor. Furthermore, phorbol myristate acetate (PMA), a PKC stimulant, but not dibutyryl cyclic AMP, a protein kinase A stimulant, stimulated the accumulation of HSP27. Interestingly, SB203580 did not inhibit PMA-stimulated HSP27 induction. These results strongly suggest that TNF-α may act as the regulator of HSP27 induction in neutrophils. p38 MAP kinase (but not p44/p42 MAP kinase) and PKC take part in TNF-α-stimulated HSP27 induction in human neutrophils.