Maru Y, Afar D E, Witte O N, Shibuya M
Department of Genetics, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108, Japan.
J Biol Chem. 1996 Jun 28;271(26):15353-7. doi: 10.1074/jbc.271.26.15353.
Bcr-Abl oncoproteins are responsible for the pathogenesis of human leukemias with a reciprocal chromosome translocation t(9;22). The amino-terminal Bcr sequence has a potential to form a homotetramer (tetramer domain), and destructions of the tetramer domain cause a complete loss of biological activities in Bcr-Abl. Here we show that Bcr-Abl in which the tetramer domain is replaced with glutathione S-transferase (GST) with a dimerizing ability (GST/Bcr-Abl-(Delta1-160)) can no longer induce an interleukin-3 (IL-3) independence in Ba/F3 cells or transform mouse bone marrow cells but still retains by 30-40% the ability to transform Rat1 cells. Compared with the wild type Bcr-Abl, autophosphorylation of GST/Bcr-Abl-(Delta1-160) in vivo was reduced by more than 50%. The Grb-2 binding to GST/Bcr-Abl-(Delta1-160) was 50% reduced in Rat1 cells and undetectable in Ba/F3 cells. In Rat1 cells expressing GST/Bcr-Abl-(Delta1-160), phosphotyrosine contents of p62 and Shc were 70% decreased.
Bcr-Abl癌蛋白与相互易位的染色体t(9;22)相关，是人类白血病发病机制的关键因素。Bcr序列的氨基末端具有形成同四聚体的潜力（四聚体结构域），而该结构域的破坏会导致Bcr-Abl的生物活性完全丧失。在此我们发现，将四聚体结构域替换为具有二聚化能力的谷胱甘肽S-转移酶（GST）的Bcr-Abl（GST/Bcr-Abl-(Delta1-160)），不再能使Ba/F3细胞产生白细胞介素-3（IL-3）非依赖性，也无法转化小鼠骨髓细胞，但仍保留30%-40%转化Rat1细胞的能力。与野生型Bcr-Abl相比，GST/Bcr-Abl-(Delta1-160)在体内的自磷酸化水平降低了50%以上。在Rat1细胞中，Grb-2与GST/Bcr-Abl-(Delta1-160)的结合减少了50%，而在Ba/F3细胞中则无法检测到。在表达GST/Bcr-Abl-(Delta1-160)的Rat1细胞中，p62和Shc的磷酸酪氨酸含量降低了70%。
