Bayle Julie, Letard Sébastien, Frank Ronald, Dubreuil Patrice, De Sepulveda Paulo
Institut National de la Santé et de la Recherche Médicale (INSERM) U119, Laboratoire d'Hématopoïèse Moléculaire et Fonctionnelle, 27 Boulevard Lei Roure, 13009 Marseille, France.
J Biol Chem. 2004 Mar 26;279(13):12249-59. doi: 10.1074/jbc.M313381200. Epub 2004 Jan 5.
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.
细胞因子信号转导抑制因子（SOCS）蛋白是一类含Src同源2结构域的衔接蛋白家族。细胞因子诱导的含Src同源结构域2的蛋白、SOCS1、SOCS2和SOCS3参与细胞因子信号转导的下调。SOCS4、5、6和7的功能尚不清楚。KIT受体信号转导受蛋白酪氨酸磷酸酶和衔接蛋白的调节。我们先前报道SOCS1抑制干细胞因子（SCF）诱导的细胞增殖。通过筛选SOCS家族的其他成员，我们鉴定出SOCS6是一种KIT结合蛋白。利用KIT突变体和肽段，我们证明SOCS6直接结合到近膜结构域的KIT酪氨酸567位点。为了研究这种相互作用的功能，我们在细胞系中组成性表达SOCS6。在Ba/F3-KIT细胞系中异位表达SOCS6可降低对SCF的细胞增殖反应，但不影响SCF诱导的趋化作用。在Ba/F3、小鼠胚胎成纤维细胞（MEF）或COS-7细胞中，SOCS6可降低SCF诱导的ERK1/2和p38的激活，但不影响AKT或STATs的激活。SOCS6不影响其他刺激对ERK和p38的激活。这些结果表明，SOCS6结合到KIT近膜区域，影响导致MAPK激活的上游信号成分。我们的结果表明，KIT信号转导受多种SOCS蛋白的调节，并提示SOCS6作为受体酪氨酸激酶负调节因子的假定功能。
