Growth and Differentiation through the Cytokine Receptors

促红细胞生成素(EPO)与其膜受体相互作用可诱导红系祖细胞增殖分化。EPO已被证明在各种造血细胞系中激活JAK2-STAT5通路，尽管该通路的生理作用尚不清楚。我们在嵌合受体的胞浆区域引入了不同的缺失和酪氨酸(Y)对苯丙氨酸(F)的替换，并在EPO反应的红白血病细胞系Elm-I-1中表达了这些突变的嵌合体。我们发现EPO受体的Y343或Y401对于红系分化和STAT5激活是独立必需的。我们寻找了即刻早期的细胞因子反应基因，并分离到一个新的基因CIS(细胞因子诱导的SH2包含蛋白)，它是由STAT5诱导的。我们克隆了CIS基因的5‘侧翼区，发现转录起始点上游约200个碱基含有4个潜在的START5结合位点(MGF盒)。Cis含有SH2结构域，与酪氨酸磷酸化的EPO和IL3受体结合。顺式调节蛋白是STAT5的反馈调节器，它的表达受STAT5的诱导，并通过与受体结合负向调节STAT5的激活。我们目前正在通过创造转基因和基因敲除小鼠来研究CIS的功能。我们还发现了一个新的CIS相关分子Jab，Jab是以JAK2酪氨酸激酶结构域为诱饵，通过酵母双杂交克隆出来的。Jab是JAK激酶的负性调节因子，可能抑制细胞因子的各种作用。我们正在研究JAB的功能。

Interaction between erythropoietin (EPO) and its membrane receptor induces the proliferation and differentiation of erythroid progenitors. EPO has been shown to activate the JAK2-STAT5 pathway in various hematopoietic cell lines, although the physiological role of this pathway is unclear. We introduced various deletion and tyrosine (Y) to phenylalanine (F) substitution in the cytoplasmic domain of the chimeric receptor and expressed these mutant chimeras in an EPO-responsive erythroleukemia cell line, ELM-I-1. We found that Y343 or Y401 of the EPO receptor are independently necessary for erythroid differentiation as well as STAT5 activation. We searched for immediate early cytokine responsive genes and isolated a novel gene, CIS (Cytokine Inducible SH2 containing protein) that is induced through STAT5. We cloned the 5'-flanking region of the CIS gene, and found that about 200 bases upstream of the transcription-initiation site contain four potential START5 binding sites (MGF boxes). CIS contains an SH2 domain and binds to tyrosine-phosphorylated EPO and IL3 receptors. CIS is a feedback modulator of STAT5 ; its expression is induced by STAT5 and it negatively modulates STAT5 activation by binding to the receoptor. We are currently investigating the function of CIS by creating transgenic and knockout mice. We also found a novel CIS related molecule, JAB,JAB was cloned by yeast two-hybrid using JAK2 tyrosine kinase domain as bait. JAB is a negative regulator of JAK kinases ans probably inhibits various action of cytokines. We are studying the function of JAB.