SOCS1 Inhibits Tumor Necrosis Factor-induced Activation of ASK1-JNK Inflammatory Signaling by Mediating ASK1 Degradation

Rong Zhang,Haifeng Zhang,Wei Zhang,Wang Min,Yun He

doi:10.1074/jbc.m512338200

Abstract

We have previously shown that ASK1 undergoes ubiquitination and degradation in resting endothelial cells (EC) and that proinflammatory cytokine tumor necrosis factor (TNF) induces deubiquitination and stabilization, leading to ASK1 activation. However, the mechanism for the regulation of ASK1 stability is not known. In the present study, we have shown that SOCS1, a member of suppressor of cytokine signaling, induces ASK1 degradation. SOCS1 was constitutively expressed in EC and formed a labile complex with ASK1 that can be stabilized by proteasomal inhibitors. The phosphotyrosine-binding SH2 domain of SOCS1 was critical for its association with ASK1. Thus a SOCS1 mutant defective in phosphotyrosine binding failed to bind to and induce ASK1 degradation. Phosphotyrosine of ASK1 was induced in response to growth factors, and TNF induced dephosphorylation and dissociation of ASK1 from SOCS1. ASK1 with a mutation at Tyr-718 diminished the binding to SOCS1, suggesting that the phosphotyrosine-718 of ASK1 is critical for SOCS1 binding. Moreover, ASK1 expression and activity were up-regulated in SOCS1-deficient mice and derived EC, resulting in enhanced TNF-induced activation of JNK, expression of proinflammatory molecules, and apoptotic responses. We concluded that SOCS1 functions as a negative regulator in TNF-induced inflammation in EC, in part, by inducing ASK1 degradation.

Highlights

Gene expression of proinflammatory molecules such as E-selectin and VCAM-1 [2]
We have shown that SOCS1 via its SH2 domain binds to the phosphotyrosine residues on Apoptosis signal-regulating kinase 1 (ASK1) to induce ASK1 degradation in an elongin complex-dependent manner
These data suggest that SOCS1 and SOCS3 might bind to ASK1 and induce ASK1 degradation

Summary

Introduction

Gene expression of proinflammatory molecules such as E-selectin and VCAM-1 [2]. Apoptosis signal-regulating kinase 1 (ASK1), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is an upstream activator of JNK/p38 MAPK cascades [3]. To confirm that SOCS1-DC is defective in binding to elongin B/C, FLAG-SOCS1, HA-tagged elongin B, and elongin C were co-transfected in EC, and association of SOCS1 with elongin B/C was determined by immunoprecipitation assay with anti-FLAG antibody followed by Western blot with anti-HA antibody. Similar results were obtained in a reciprocal immunoprecipitation assay (i.e. cell lysates were immunoprecipitated by anti-ASK1 followed by Western blot with anti-SOCS1) (Fig. 4c).

Results

Conclusion