Genes Differentially Expressed During Tumor Progression

mRNA的差异显示已被用于鉴定其表达可驱动或阻止进展为肿瘤细胞表型的基因。一种这样的基因，金属蛋白酶组织抑制剂TIMP-3），在肿瘤前而非肿瘤性JB 6细胞中表达（Sun等人，Cancer Res，1994; Sun等人，J Biol Chem，1995），并且发现当在人DLD结肠癌细胞中表达时充当肿瘤抑制因子（Bian等人，致癌作用，1996年）。TIMP-3的转录沉默可归因于其启动子的序列特异性甲基化（Pennie等人，Cell Growth and Diff，1999）。反义DNA甲基转移酶的表达恢复了肿瘤细胞TIMP-3的表达，并重现了肿瘤前JB 6细胞中与TIMP-3表达相关的相同位点的非甲基化状态。进行单独的差异显示分析以鉴定可能介导或抑制肿瘤启动子依赖性进展阶段的基因表达。全长cDNA克隆已被分离的两个基因中优先表达的促进抗性小鼠JB 6细胞。一种指定为pdcd 4（Cmarik等人，PNAS 1999，是新的;另一种是plekstrin（Cmarik et al Genomics 2000）。新pdcd 4基因的反义表达将P-细胞转化为P+细胞，而pdcd 4正义表达（Yang et al Oncogene 2001）将P+细胞转化为P-细胞，从而建立了与预防肿瘤启动子诱导的转化的因果关系。目前的研究主要集中在pdcd 4蛋白的分子功能和定位。pdcd 4对已知肿瘤促进所需的分子事件的可能抑制作用的检查显示，pdcd 4表达抑制转录因子AP-1的活化，但不抑制NF κ B或鸟氨酸脱羧酶的活化（Yang et al Oncogene 2001）。虽然Pdcd 4蛋白的表达阻断AP-1活化，但Pdcd 4不直接与Jun或Fos蛋白相互作用。通过酵母双杂交分析pdcd 4结合伙伴揭示了作为主要结合伙伴的翻译起始因子之一。目前的研究主要集中在确定Pdcd 4在调节蛋白质翻译中的功能意义以及鉴定可能被Pdcd 4表达抑制的特异性转化相关mRNA。最后，我们已经发现，在促进敏感细胞中，染色质蛋白HMG I（Y）的表达优先由肿瘤促进剂诱导（Cmarik等，Oncogene，1998），并且正在研究这一点的因果意义以及HMG I（Y）（现在为HMGA 1）作为转化相关AP-1靶基因的可能状态。

Differential display of mRNA has been used to identify genes whose expression may drive or prevent progression to tumor cell phenotype. One such gene, tissue inhibitor of metalloproteinases TIMP-3), was expressed in preneoplastic but not neoplastic JB6 cells (Sun et al., Cancer Res, 1994; Sun et al., J Biol Chem, 1995) and was found to act as a tumor suppressor when expressed in human DLD colon carcinoma cells (Bian et al., Carcinogenesis, 1996). The transcriptional silencing of TIMP-3 is attributable to sequence specific methylation of its promoter (Pennie et al., Cell Growth and Diff, 1999). Expression of antisense DNA methyl transferase restored expression of TIMP-3 to tumor cells and recapitulated the unmethylated status of the same sites associated with TIMP-3 expression in preneoplastic JB6 cells. A separate differential display analysis was carried out to identify gene expression that may mediate or inhibit tumor promoter dependent stages of progression. Full-length cDNA clones have been isolated for two genes preferentially expressed in promotion resistant mouse JB6 cells. One designated pdcd4 (Cmarik et al., PNAS 1999, is novel; the other is plekstrin (Cmarik et al Genomics 2000). Antisense expression of the novel pdcd4 gene converts P- to P+ cells and pdcd4 sense expression (Yang et al Oncogene 2001) converts P+ to P- cells, thus establishing a causal relationship to prevention of tumor promoter induced transformation. Current studies focus on the molecular function and localization of pdcd4 protein. Examination of the possible inhibitory effect of pdcd4 on molecular events known to be required for tumor promotion revealed that pdcd4 expression inhibited the activation of transcription factor AP-1 but not of NFkappa B or of ornithine decarboxylase(Yang et al Oncogene 2001). Although expression of Pdcd4 protein blocks AP-1 activation, Pdcd4 does not interact directly with Jun or Fos proteins. Analysis of pdcd4 binding partners by a yeast two-hybrid assay revealed one of the translation initiation factors as a major binding partner. Current research is focused on determining the functional significance of Pdcd4 in regulating protein translation and on identifying specific transformation relevant mRNAs whose translation may be inhibited by Pdcd4 expression. Finally, we have discovered that expression of the chromatin protein(s)HMG I(Y) is preferentially induced by tumor promoters in promotion sensitive cells (Cmarik et al, Oncogene, 1998), and are investigating the causal significance of this as well as the possible status of HMG I(Y) (now HMGA1) as a transformation relevant AP-1 target gene.