MOLECULAR PATHOGENESIS OF CANCER OF MUTATOR PHENOTYPE

微卫星突变表型（microsatellite mutator phenotype， MMP）的胃肠道癌在基因型和表型上与没有MMP的肿瘤不同。APC、p53和K-ras癌基因通常在MMP-肿瘤中发生突变，而TGFbetaRII和BAX的突变失活基本上仅限于MMP+肿瘤。我们提出MMP通路的存在和独特的癌症特征，遗传性非息肉病性结直肠癌（HNPCC）综合征肿瘤和大约15%的散发性胃肠道癌症的特征，最终取决于MMP靶序列在某些癌症基因中的存在。在具体目标1中，我们将检验mmp依赖性癌症通路存在的假设。我们建议研究有或没有MMP的肿瘤在基因型上的差异。我们将完成MMP+和MMP-结肠肿瘤中APC抑制基因突变的筛选（1a）；确定MMP+和MMP-胃肠道肿瘤之间的基因型差异是否也延伸到我们在结肠癌、乳腺癌和前列腺癌中观察到的DNA甲基化的广泛体细胞变化，特别是在同源盒基因家族中（1b）；并利用MMP癌症的特殊表型特征来开发遗传性和散发性MMP癌症的诊断分析（1c）。在具体目标2中，我们将检验MMP通过多个突变基因的突变失活逐渐展开的假设。我们提出研究“突变子使另一个突变子发生突变”的模型。我们将完成对结直肠癌和胃MMP+腺癌已知DNA错配修复（MMR）基因家族成员突变的筛查（2a）；对单个MMR突变基因的突变影响及其在肿瘤细胞突变谱中的组合进行功能分析（2b）；并确定这些发现对MMP癌症的预后价值（2c）。在具体目标3中，我们将验证细胞凋亡逃逸是MMP肿瘤发生的关键事件的假设。我们拟探讨BAX突变失活对MMP肿瘤细胞凋亡逃逸和肿瘤发生的作用机制。我们将完成对MMP+和MMP-肿瘤BAX突变的筛选（3a）；通过体内和体外实验对BAX基因失活在MMP癌症中的作用进行功能分析（3b）；探讨BAX体细胞突变失活对MMP癌的预后价值。

Gastrointestinal cancers of the microsatellite mutator phenotype (MMP) differ in genotype and phenotype from tumors without the MMP. APC, p53 and K-ras cancer genes are commonly mutated in MMP- tumors while mutational inactivation of TGFbetaRII and BAX is essentially restricted to MMP+ cancers. We propose that the existence and distinctive features of the MMP pathway for cancer, characteristic of tumors of the Hereditary Non-Polyposis Colorectal Cancer (HNPCC) syndrome and about 15% of sporadic gastrointestinal cancers, ultimately depends on the presence in some cancer genes of sequences target for the MMP. In specific aim 1 we will test the hypothesis of the existence of a MMP-dependent pathway for cancer. We propose to investigate the differences in genotype between tumors with or without the MMP. We will complete the screening of mutations in the APC suppressor gene in MMP+ and MMP- colon tumors (1a); determine whether the differences in genotype between MMP+ and MMP- gastrointestinal tumors also extend to widespread somatic changes in DNA methylation that we have observed in colon, breast and prostate cancer, specifically in the homeobox gene family (1b); and exploit the peculiar phenotypic features of MMP cancer to develop diagnostic assays for hereditary and sporadic cancer of the MMP (1c). In specific aim 2 we will test the hypothesis that the MMP unfolds gradually by the mutational inactivation of multiple mutator genes. We propose to investigate the model of the "mutator that mutates another mutator". We will complete the screening of colorectal and gastric MMP+ adenocarcinomas for mutations in the known members of the DNA mismatch repair (MMR) gene family (2a); perform a functional analysis of the effect of mutations in individual MMR mutator genes and their combinations in the spectra of mutations in the tumor cells (2b); and establish the prognostic value of these findings for cancer of the MMP (2c). In specific aim 3 we will test the hypothesis that the escape from apoptosis is a critical event in tumorigenesis of the MMP. We propose to investigate the mechanisms by which BAX mutational inactivation contributes to the escape from apoptosis and to tumorigenesis of tumors cells of the MMP. We will complete the screening of MMP+ and MMP- tumors for mutations in BAX (3a); perform a functional analysis of the role of BAX gene inactivation in cancer of the MMP by in vivo and in vitro assays (3b); and investigate the prognostic value of BAX somatic mutational inactivation for cancer of the MMP.