Characterization of Human 3p Recessive Oncogenes

本项目主要研究人类3p隐性癌基因（tumor suppressor genes, TSGs）的鉴定和功能表征，最初重点是在肺癌和乳腺癌中发现63kb的完全测序的3p21.3区域纯合缺失的TSGs。我们的总体假设是，这些基因中的一个或多个的双等位基因失活或单倍不足在许多人类癌症的发病机制中具有重要意义，并且这种失活发生在多步骤癌变过程的早期。我们刚刚完成了该区域25个基因的分离和初步鉴定（其中23个是新发现的），并发现两个双等位基因表达缺失，RASSF1A （Ras与DAG结合域相互作用蛋白）和SEMA3B（分泌III类信号蛋白）具有有效的肿瘤抑制活性。我们还发现其他几个具有TSGs的一些特征（表达缺失、突变、恶性表型抑制），包括CACNA2D2、101F6、NPR21/G21、BLU、FUSI、HYAL1和FUS2。目前的提案将：通过体外和体内异种移植试验，确认RASSF1A和SEMA3B的肿瘤抑制功能，并进一步暗示或排除多种具有不同遗传异常的人类癌细胞系中的其他候选3p21.3 TSGs (Aim 1)；证实肿瘤获得性RASSF1A和SEMA3B以及其他一些3p21.3 TSG候选基因的表达缺失发生在人类癌症中，而不是在正常组织中，这可以通过肿瘤获得性启动子区域CpG岛的甲基化来解释（Aim 2）；利用人癌细胞系研究RASSF1A和SEMA3B抑制肿瘤的潜在机制，从而确定RASSF1A和SEMA3B抑制肿瘤表型的通路；在此过程中还确定这些基因的获得性和种系氨基酸序列改变是否使其功能失活，从而可能导致癌症的发生（目的3）；确定致癌物刺激Sema3b敲除小鼠模型是否证实Sema3b为TSG，并检测Sema3b单倍不足是否足以辅助致癌物诱导的小鼠肺癌。(4)目标。这些基因的特征最终将为新的癌症诊断和治疗方法的发展带来转化效益，包括用于癌症的早期检测、预防和治疗。

This project focuses on identification and functional characterization of human 3p recessive oncogenes (tumor suppressor genes, TSGs), with the initial emphasis being on discovery of TSGs in a 630 kb, completely sequenced, 3p21.3 region found to be homozygously deleted in lung and breast cancers. Our overall hypothesis is that biallelic inactivation or haploinsufficiency of one or more of these genes is of fundamental importance in the pathogenesis of many human cancers and that this inactivation occurs early in the multistep process of carcinogenesis. We have just completed the isolation and initial characterization of 25 genes in this area (23 of which are new) and found two, RASSF1A (Ras interacting protein with a DAG binding domain), and SEMA3B (secreted class III semaphorin) to have biallelic expression loss and potent tumor suppressing activity. We also found several others to have some characteristics of TSGs (loss of expression, mutation, suppression of the malignant phenotype) including CACNA2D2, 101F6, NPR21/G21, BLU, FUSI, HYAL1, and FUS2. The current proposal will: Confirm the tumor suppressing function of RASSF1A and SEMA3B and further implicate or dismiss the other candidate 3p21.3 TSGs in multiple human cancer cell lines with different genetic abnormalities by in vitro and in vivo xenograft assays (Aim 1); Confirm that tumor acquired loss of expression of RASSF1A and SEMA3B and some of the other 3p21.3 TSG candidates occurs in human cancers but not in normal tissues, and is explained by tumor acquired methylation of CpG islands in their promoter regions (Aim 2); Study the potential mechanisms for tumor suppression of RASSF1A and SEMA3B using human cancer cell lines and thus determine the pathways involved in RASSF1A and SEMA3B suppression of the tumor phenotype; in the process also determine if acquired and germline amino acid sequence alterations in these genes inactivate their function potentially predisposing to cancer development (Aim 3); Determine whether a Sema3b knockout mouse model challenged with carcinogens confirms SEMA3B as a TSG and also test whether SEMA3B haploinsufficiency is sufficient for aiding carcinogen induced lung cancer in the mouse. (Aim 4). The characterization of these gene(s) should ultimately have translational benefit for the development of new cancer diagnostics and therapeutics, including use in cancer early detection, prevention, and treatment.