SOCS/CIS protein inhibition of growth hormone-stimulated STAT5 signaling by multiple mechanisms
SOCS/CIS protein inhibition of growth hormone-stimulated STAT5 signaling by multiple mechanisms
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DOI：
10.1074/jbc.274.50.35553
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发表时间：
1999-12-10
影响因子：
4.8
通讯作者：
Waxman, DJ
中科院分区：
文献类型：
--
作者：
Ram, PA;Waxman, DJ
在转染COS细胞中，研究了生长激素（GH）诱导型细胞因子信号抑制因子（SOCS/CIS）家族的5个成员对GH信号的抑制作用。在表达SOCS-1或SOCS-3时观察到信号转导子STAT 5 b的GH激活和STAT 5 b依赖性转录活性的完全抑制，而在其他SOCS/CIS家族成员中观察到部分抑制（CIS，SOCS-2）或无抑制（SOCS-6）。SOCS-1、SOCS-2、SOCS-3和CIS均强烈抑制在低水平转染JAK 2时观察到的JAK 2的GH受体（GHR）依赖性酪氨酸磷酸化;然而，只有SOCS-1强烈抑制在较高JAK 2水平时观察到的JAK 2的GHR非依赖性酪氨酸磷酸化。为了探测与GHR的相互作用，使用谷胱甘肽S-转移酶-GHR融合蛋白进行体外结合测定，所述融合蛋白含有可变长度的GHR的COOH末端胞质结构域。CIS和SOCS-2结合到含有少至80个COOH-末端GHR残基的融合蛋白，只要融合蛋白是酪氨酸磷酸化的。相比之下，SOCS-3的结合需要酪氨酸磷酸化的GHR膜近端序列，SOCS-1的结合是酪氨酸磷酸化独立的，SOCS-6不结合GHR融合蛋白。GHR的近膜酪氨酸残基333和338突变为苯丙氨酸抑制了SOCS-3对GH信号传导至STAT 5 b的抑制，但CIS没有抑制。因此，SOCS/CIS蛋白可以通过三种不同的机制抑制GH向STAT 5 b的信号传导，这三种不同的机制通过它们在GHR-JAK 2信号传导复合物内的分子靶标来区分，如SOCS-1（直接JAK 2激酶抑制）、SOCS-3（通过膜近端GHR酪氨酸333和338抑制JAK 2信号传导）以及CIS和SOCS-2（通过膜远端酪氨酸抑制）所例示。
The inhibition of growth hormone (GH) signaling by five members of the GH-inducible suppressor of cytokine signaling (SOCS/CIS) family was investigated in transfected COS cells. Complete inhibition of GH activation of the signal transducer STAT5b and STAT5b-dependent transcriptional activity was observed upon expression of SOCS-1 or SOCS-3, while partial inhibition (CIS, SOCS-2) or no inhibition (SOCS-6) was seen with other SOCS/CIS family members. SOCS-1, SOCS-2, SOCS-3, and CIS each strongly inhibited the GH receptor (GHR)-dependent tyrosine phosphorylation of JAK2 seen at low levels of transfected JAK2; however, only SOCS-1 strongly inhibited the GHR-independent tyrosine phosphorylation of JAK2 seen at higher JAK2 levels. To probe for interactions with GHR, in vitro binding assays were carried out using glutathione S-transferase-GHR fusion proteins containing variable lengths of GHR's COOH-terminal cytoplasmic domain. CIS and SOCS-2 bound to fusions containing as few as 80 COOH-terminal GHR residues, provided the fusion protein was tyrosine-phosphorylated. By contrast, SOCS-3 binding required tyrosine-phosphorylated GHR membrane-proximal sequences, SOCS-1 binding was tyrosine phosphorylation-independent, and SOCS-6 did not bind the GHR fusion proteins at all. Mutation of GHR's membrane-proximal tyrosine residues 333 and 338 to phenylalanine suppressed the inhibition by SOCS-3, but not by CIS, of GH signaling to STAT5b. SOCS/CIS proteins can thus inhibit GH signaling to STAT5b by three distinct mechanisms, distinguished by their molecular targets within the GHR-JAK2 signaling complex, as exemplified by SOCS-1 (direct JAK2 kinase inhibition), SOCS-3 (inhibition of JAK2 signaling via membrane-proximal GHR tyrosines 333 and 338), and CIS and SOCS-2 (inhibition via membrane-distal tyrosine(s)).