Regulation of TNF mediated antiapoptotic signaling in human neutrophils: role of δ-PKC and ERK1/2

Abstract

TNF is implicated in the suppression of neutrophil apoptosis during sepsis. Multiple signaling pathways are involved in TNF-mediated antiapoptotic signaling; a role for the MAP kinases (MAPK), ERK1/2, and p38 MAPK has been suggested. Antiapoptotic signaling is mediated principally through TNF receptor-1 (TNFR-1), and the PKC isotype-delta (δ-PKC) is a critical regulator of TNFR-1 signaling. δ-PKC associates with TNFR-1 in response to TNF and is required for NFκB activation and inhibition of caspase 3. The role of δ-PKC in TNF-mediated activation of MAPK is not known. The purpose of this study was to determine whether the MAPK, ERK1/2, and p38 MAPK are involved in TNF antiapoptotic signaling and whether δ-PKC is a key regulator of MAPK activation by TNF. In human neutrophils, TNF activated both p38 MAPK and ERK1/2 principally via TNFR-1. The MEK1/2 inhibitors PD098059 and U0126, but not the p38 MAPK inhibitor SB203580, decreased TNF antiapoptotic signaling as measured by caspase 3 activity. A specific δ-PKC antagonist, V1.1δ-PKC-Tat peptide, inhibited TNF-mediated ERK1/2 activation, but not p38 MAPK. ERK1/2 inhibition did not alter recruitment of δ-PKC to TNFR-1, indicating δ-PKC is acting upstream of ERK1/2. In HL-60 cells differentiated to a neutrophilic phenotype, δ-PKC depletion by δ-PKC siRNA resulted in inhibition of TNF mediated ERK1/2 activation but not p38 MAPK. Thus, ERK1/2, but not p38 MAPK, is an essential component of TNF-mediated antiapoptotic signaling. In human neutrophils, δ-PKC is a positive regulator of ERK1/2 activation via TNFR-1 but has no role in p38 MAPK activation.