P38-dependent Enhancement of Cytokine-induced Nitric-oxide Synthase Gene Expression by Heat Shock Protein 70

Kerstin Bellmann,Volker Burkart,Joerg Bruckhoff,Hubert Kolb,Jacques Landry

doi:10.1074/jbc.m000340200

Abstract

Heat shock protein (hsp) 70 protects cells against stress by means of its ability to chaperone denatured proteins and to modulate stress-activated signaling pathways. Because inflammatory processes are often accompanied by hsp expression and because stress and cytokines share several signaling pathways, we investigated the possibility that hsp70 might modulate the cellular response to cytokines. We found that stable cell clones overexpressing hsp70, or cells shortly after transfection with hsp70, produced 2 times more nitric oxide and inducible nitric-oxide synthase (iNOS) protein and mRNA in response to cytokines than control cells expressing undetectable amounts of hsp70. Since mitogen-activated protein kinases participate in the activation of iNOS by cytokines, we investigated whether hsp70 affected the activation of these signaling pathways. hsp70 overexpression led to a specific enhancement of the activation of the p38 pathway by cytokines, producing little or no effect on the activation of extracellular signal-regulated kinase or Jun N-terminal kinase. Blocking p38 activity with SB203580 totally abolished the enhancing effect of hsp70 on cytokine-induced endogenous iNOS mRNA accumulation or transcription of an iNOS promoter-driven luciferase gene, while having little effect on the cytokine response observed in control cells. We conclude that the p38 pathway acts as an enhancing factor in the activation of iNOS by cytokines and that hsp70 can modulate the cellular response to cytokines by acting on signaling elements upstream of p38.

Highlights

Heat shock protein 70 protects cells against stress by means of its ability to chaperone denatured proteins and to modulate stress-activated signaling pathways
We found that stable cell clones overexpressing hsp70, or cells shortly after transfection with hsp70, produced 2 times more nitric oxide and inducible nitric-oxide synthase protein and mRNA in response to cytokines than control cells expressing undetectable amounts of hsp70
Since mitogenactivated protein kinases participate in the activation of inducible nitric-oxide synthase (iNOS) by cytokines, we investigated whether hsp70 affected the activation of these signaling pathways. hsp70 overexpression led to a specific enhancement of the activation of the p38 pathway by cytokines, producing little or no effect on the activation of extracellular signal-regulated kinase or Jun N-terminal kinase

Summary

EXPERIMENTAL PROCEDURES

Materials—[␥-32P]ATP (3000 Ci/mmol) was purchased from NEN Life Sciences Products (Boston, MA). Luciferase Assay—After treatment for 6 h the cells were scraped in 150 ␮l of lysis buffer (25 mM Hepes, pH 7.40, 1 mM EGTA, 1 mM EDTA, 8 mM MgCl2, 10% glycerol, 1 mM dithiothreitol, 1 mM phenylmethylsulfonyl fluoride, 1% Triton X-100). After stimulation the cells were scraped in lysis buffer containing 20 mM MOPS, pH 7.0, 10% glycerol, 80 mM ␤-glycerophosphate, 5 mM EGTA, 0.5 mM EDTA, 1 mM Na3VO4, 5 mM Na4P2O7, 50 mM sodium fluoride, 1% Triton X-100, 1 mM benzamidine, 1 mM dithiothreitol, and 1 mM phenylmethylsulfonyl fluoride. The kinase activity was assayed for 30 min at 30 °C and stopped by boiling in SDS sample buffer. The assay buffer for p38 contained 50 mM Hepes, pH 7.4, 50 mM ␤-glycerophosphate, 50 mM MgCl2, 0.2 mM Na3VO4, 4 mM dithiothreitol, ATF2-GST, and [␥-32P]ATP. The activity of the various kinases was quantified by measuring the incorporation of radioactivity into the specific substrate by PhosphorImager analysis after electrophoresis

RESULTS

DISCUSSION