MOUSE MODEL FOR THE PEUTZ JEGHERS SYNDROME

Peutz-Jeghers综合征（PJS）是一种独特的常染色体显性综合征，其特征是在小肠和结肠中出现皮肤高黑色素细胞斑和相关的错构瘤息肉。这些患者患各种不同肿瘤的风险也显著增加，包括小肠、结肠、胰腺、胃、乳房、卵巢和睾丸的肿瘤。PJS是由编码丝氨酸苏氨酸激酶LKB1基因的种系突变引起的。最近的证据表明LKB1基因是PJS患者错构瘤和腺癌的肿瘤抑制因子。虽然该基因的功能尚不清楚，但Mehennni等人（1998）研究的LKB1突变通过自磷酸化检测都导致激酶活性丧失。这是已知的第一个因激酶活性丧失而易患癌症的蛋白激酶。该提案的总体目标是为PJS生成一个动物模型。这将使我们能够进行更多的长期研究，从而开发PJS患者检测的功能分析，开发通过PJS途径引起的癌症的早期检测策略，以及开发PJS癌症的预防策略。该动物模型的研究也将有助于阐明LKB1的正常功能，以及该基因破坏增加PJS相关癌症风险的机制。将产生lkb1基因的条件敲除转基因小鼠系。将检查由小鼠LKB1等位基因之一的破坏引起的表型。大多数PJS患者有一个LKB1等位基因为空，第二个等位基因在错构瘤和腺癌中丢失或突变。据推测，具有一个空等位基因的小鼠将具有与PJS相似的表型。将确定由lkb1基因纯合子破坏产生的表型。如果纯合子基因敲除小鼠无法存活，将创建组织特异性条件敲除小鼠，以便研究lkb1基因在胃肠道组织（包括胰腺）中的作用。如果在小鼠中未观察到腺癌，则将携带lkb1零等位基因的活小鼠与携带p53零等位基因的小鼠杂交。这些小鼠的表型将被检查，以确定敲除lkb1是否加速了小鼠肿瘤发生的途径。由于p53突变在PJS患者腺癌中经常发生，因此p53突变与lkb1空等位基因的结合将为PJS的肿瘤发生途径提供两个线索。

Peutz-Jeghers syndrome (PJS) is a unique autosomal dominant syndrome characterized by cutaneous hypermelanocytic macules and associated hamartomatous polyp develop in the small bowel and colon. These patients also have a dramatically increased risk for development of a variety of different neoplasias including those of the small bowel, colon, pancreas, stomach, breast, ovary and testicle. PJS is caused by germline mutations in the gene encoding the serine threonine kinase LKB1. Recent evidence that the LKB1 gene is a tumor suppressor in hamartomas and adenocarcinomas from PJS patients. Although the function of the gene is not known, the LKB1 mutations studied by Mehennni et al. (1998) all caused a loss of kinase activity when assayed by auto-phosphorylation. This is the first known protein kinase that predisposes to cancer because of a loss of the kinase activity. The overall goal of the proposal is to generate an animal model for PJS. This will allow us to conduct more long-term studies leading to the development of functional assays for the detection of patients with PJS, the development of early detection strategies for cancer arising via the PJS pathway, and the development of preventive strategies for PJS cancers. Studies of the proposed animal model will also lead to the elucidation of the normal function of LKB1 and the mechanism by which disruption of this gene increases risk for PJS associated cancers. A conditional knock-out transgene mouse line for the lkb1 gene will be generated. The phenotype resulting from disruption of one of the mouse LKB1 alleles will be examined. Mot humans with PJS have one null allele for LKB1, the second allele is lost or mutated in hamartomas and adenocarcinomas. It is hypothesized that mice with one null allele will have a phenotype similar to the PJS. The phenotype resulting from the homozygous disruption of the lkb1 gene will be determined. If homozygous knock-out mice are not viable, tissue-specific conditional knock-out mice will e created to allow the effects of the lkb1 gene in the gastrointestinal tissues (including pancreas) to be studied. If adenocarcinomas are not observed in mice as a result of carrying out the aims described above, viable mice carrying lkb1 null alleles will be crossed with mice carrying a p53 null allele. The phenotype of these mice will be examined to determine if knocking out lkb1 accelerates the pathway for tumorigenesis in the mice. Because mutations in p53 are known to occur frequently in adenocarcinomas of PJS patients, the combination of the p53 mutation and the lkb1 null allele would provide two hints in the PJS pathway of tumorigenesis.