Functional analysis of truncated Notch 1 gene products generated by insertions of mouse mammary tumor proviruses in development of mouse lymphomas.

Notch基因家族编码一种跨膜受体，在果蝇和脊椎动物的整个发育过程中控制细胞命运的决定。Notch蛋白的氨基端编码细胞外结构域，包含多达36个参与配体结合的egf样基序和3个功能未知的Notch/lin-12基序。Notch的细胞内部分的特征是cdcl0/锚蛋白基序的6个串联拷贝，被认为参与蛋白质-蛋白质相互作用。小鼠中已知Notch家族的4个成员（Notch 1至Notch 4）。虽然Notch受体可以被一系列配体激活，如Delta，但它们也可以被细胞外结构域的截断所激活。因为与人类T细胞急性淋巴细胞白血病亚群相关的染色体易位导致截断的Notch 1过表达，缺乏egf样重复序列。在小鼠乳腺肿瘤病毒（MMTV）诱导的乳腺肿瘤中，Notch 4类似的截断形式具有致癌蛋白的功能。我们在此报告了在这些MMTV LTR突变体诱导的胸腺瘤中，Notch 1基因中LTR重排的MMTV原病毒频繁插入。MMTV原病毒的插入导致Notch 1细胞内部分的截断蛋白的表达。此外，在BALB/C小鼠的自发性乳腺肿瘤中发现了细胞浆内A颗粒（IAP）中Notch 4基因的小鼠反转录转座子插入。与上述Notch 1重排类似，IAP转位导致由IAP gag序列中的14个氨基酸组成的截断的Notch 4蛋白过表达，随后是Notch 4的细胞质结构域。我们正在测试这些截断的Notch蛋白的转化活性。

The Notch gene family encodes a transmembrane receptor that controls cell fate decisions throughout development in Drosophila and vertebrate. The amino terminus of Notch proteins encodes the extra-cellular domain and contains as many as 36 repeats of EGF-like motif involved in ligand binding and three copies of Notch/lin-12 motif of unknown function. The intracellular portion of Notch is characterized by six tandem copies of cdcl0/ankyrin motif thought to be involved in protein-protein interaction. Four Notch family (Notch 1 to Notch 4) members are known in mouse. Although Notch receptors are activated by a family of ligands such as Delta, they may also be constitutively activated by truncation of the extracellular domain. Because chromo-somal translocation associated with a subset of human T cell acute lymphoblastic leukemias results in overexpression of truncated Notch 1 lacking the EGF-like repeats. Similar truncated form of Notch 4 function as oncogenic protein in mouse mammary tumor virus (MMTV) induced mammary tumor. We report here frequent insertions of MMTV proviruses with LTR rearrangement in the Notch 1 gene in the thymomas induced by these MMTV LTR mutants. MMTV provirus insertions resulted in expression of truncated proteins consist of intracellular part of Notch 1 .Furthermore intracytoplasmic A particle (IAP), a mouse retrotransposon insertion in the Notch 4 gene was found in a spontaneous mammary tumor in BALB/C mouse. Similar to Notch 1 rearrangement described above, IAP transposition led to overexpression of truncated Notch 4 protein composed of 14 amino acids from IAP gag sequence followed by the cytoplasmic domain of Notch 4. We are testing transformation activities of these truncated Notch proteins.