Suppressor of Cytokine Signaling 6 Associates with KIT and Regulates KIT Receptor Signaling

Julie Bayle,Sébastien Letard,Ronald Frank,Patrice Dubreuil,Paulo De Sepulveda

doi:10.1074/jbc.m313381200

Abstract

Suppressor of cytokine signaling (SOCS) proteins are a family of Src homology 2-containing adaptor proteins. Cytokine-inducible Src homology domain 2-containing protein, SOCS1, SOCS2, and SOCS3 have been implicated in the down-regulation of cytokine signaling. The function of SOCS4, 5, 6, and 7 are not known. KIT receptor signaling is regulated by protein tyrosine phosphatases and adaptor proteins. We previously reported that SOCS1 inhibited cell proliferation in response to stem cell factor (SCF). By screening the other members of SOCS family, we identified SOCS6 as a KIT-binding protein. Using KIT mutants and peptides, we demonstrated that SOCS6 bound directly to KIT tyrosine 567 in the juxtamembrane domain. To investigate the function of this interaction, we constitutively expressed SOCS6 in cell lines. Ectopic expression of SOCS6 in Ba/F3-KIT cell line decreased cell proliferation in response to SCF but not SCF-induced chemotaxis. SOCS6 reduced SCF-induced activation of ERK1/2 and p38 but not activation of AKT or STATs in Ba/F3, murine embryonic fibroblast (MEF), or COS-7 cells. SOCS6 did not impair ERK and p38 activation by other stimuli. These results indicate that SOCS6 binds to KIT juxtamembrane region, which affects upstream signaling components leading to MAPK activation. Our results indicate that KIT signaling is regulated by several SOCS proteins and suggest a putative function for SOCS6 as a negative regulator of receptor tyrosine kinases.

Highlights

Suppressor of cytokine signaling (SOCS) proteins are a family of Src homology 2-containing adaptor proteins
SOCS6 Protein Associates with KIT Receptor in Response to stem cell factor (SCF)—We earlier reported that SOCS1 physically associated with KIT receptor through its SH2 domain in response to KIT-ligand (SCF)-induced activation [29]
SCF induced a strong association of SOCS6 with KIT (Fig. 1) and a weak association of SOCS4 and SOCS5 with KIT

Summary

Introduction

Suppressor of cytokine signaling (SOCS) proteins are a family of Src homology 2-containing adaptor proteins. Cytokines and growth factors regulate the survival, proliferation, differentiation, and migration of hematopoietic cells Binding of these factors to transmembrane receptors induces receptor activation, which in turn results in the recruitment of signaling complexes in the vicinity of the plasma membrane. 1 The abbreviations used are: SOCS, suppressor of cytokine signaling; SH2, Src homology 2; CIS, cytokine-inducible SH2-containing protein; STAT, signal transducers and activators of transcription; E3, ubiquitinprotein isopeptide ligase; RTK, receptor tyrosine kinases; IR, insulin. The mechanisms whereby CIS, SOCS1, and SOCS3 inhibit signaling by classical cytokine receptor (i.e. receptors without catalytic activity that associate with JAK tyrosine kinases) are the best characterized. CIS binds to cytokine receptors at STAT5docking sites, which impairs recruitment of STAT5 to the receptor signaling complex and results in the down-regulation of STAT5 activation [6, 25]

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Conclusion