Exaggerated Human Monocyte IL-10 Concomitant to Minimal TNF-α Induction by Heat-Shock Protein 27 (Hsp27) Suggests Hsp27 Is Primarily an Antiinflammatory Stimulus

Abstract

Unlike more well-studied large heat shock proteins (hsp) that induce both T cell antiinflammatory (IL-10, IL-4) and macrophage proinflammatory (TNF-α, IL-15, IL-12) cytokines, hsp27, a small hsp, has been primarily identified as a substrate of mitogen-activated protein kinase-activated protein kinase-2 involved in the p38 signaling pathway and activated during monocyte IL-10 production. Hsp27 can also act as an endogenous protein circulating in the serum of breast cancer patients and a protein whose induction correlates to protection from LPS shock. However, the cytokine-stimulating properties of hsp27 have been unexplored. In this study, exogenous hsp27 is demonstrated for the first time as a potent activator of human monocyte IL-10 production, but only a modest inducer of TNF-α. Although exogenous hsp27 stimulation activated all three monocyte mitogen-activated protein kinase pathways (extracellular signal-related kinase (ERK) 1/2, c-Jun N-terminal kinase, and p38), only p38 activation was sustained and required for hsp27 induction of monocyte IL-10, while both ERK 1/2 and p38 activation were required for induction of TNF-α when using the p38 inhibitor SB203580 or the ERK inhibitor PD98059. Hsp27’s transient activation of the c-Jun N-terminal kinase pathway, which can down-regulate IL-10, may contribute to its potent IL-10 induction. Hsp27’s ERK 1/2 activation was also less sustained than activation by stimuli like LPS, possibly contributing to its modest TNF-α induction. The failure of either PD98059 or anti-TNF-α Ab to substantially inhibit IL-10 induction implied that hsp27 induces IL-10 via activation of p38 signaling independently of TNF-α activation and may be predominantly an antiinflammatory monokine stimulus.

Exogenous heat shock protein 27 uniquely blocks differentiation of monocytes to dendritic cells

“…JNK activation is also critical to DC maturation [34]. The reduced induction of MO JNK activity mediated by HSP-27 may explain its poor maturation of iDC vs. even low-dose LPS, which is a powerful JNK inducer [12,34].…”

“…We previously reported that MO IL-10, and to a lesser extent TNF-a, can be induced by exogenous HSP-27 [12]. IL-10 as well as M-CSF can significantly impair differentiation of iDC from their precursors [14].…”

“…We previously reported that HSP-27 is a potent inducer of p38 which is necessary for its IL-10 induction [12]. If the MO?iDC differentiation effects of HSP-27 treatment were directly activating MO, then p38 activation might also play a role beyond its requirement for IL-10 induction.…”

“…Untreated iDCs expressed <2% CD83. A suboptimal (50 ng) concentration of LPS was used as a maturation stimuli to allow a better comparison to HSP-27, which is a weak TNF-a inducer and may have poor autocytokineinduced maturation potential compared to LPS [12]. Suboptimal LPS still induced both significantly increased expression of CD83 (the mature DC marker) and increased DC induction of T cell proliferation in MLR (Fig.…”

“…Large HSP are thought to act as endogenous danger signals augmenting inflammatory cytokines by triggering monocyte (MO) Toll-like receptors (TLR) and scavenger receptors independently of LPS contaminants [6,7,[9][10][11]. In contrast, exogenous HSP-27 (a small HSP) predominantly stimulates MO IL-10 [12]. HSP-27 may have a dominant immunosuppressive/antiinflammatory function since IL-10 powerfully depresses MO to immature DC (iDC) (MO?iDC) differentiation and subsequent DC function [13][14][15].…”