Characterization of a Novel Growth Regulator

一种名为NNGR（新型负生长调节剂）的新基因已被克隆。NNGR编码一种分泌蛋白，该蛋白含有两个锌指状基序，并与酵母杀手毒素具有同源性。NNGR位于染色体4q21.1-22，这一区域在食管癌和结直肠癌中经常被删除。与与之匹配的正常组织相比，5/6的结肠、1/1的胃和6/7的食管肿瘤中NNGR表达缺失或降低。最重要的是，NNGR在非表达NNGR的结直肠癌细胞中的表达通过诱导凋亡抑制其生长。因此，NNGR作为一种新的生长抑制因子，其表达在原发性胃肠道（GI）癌症中缺失或减少。本研究主要针对NNGR的分子和功能特性进行研究。具体而言，我们将利用新鲜冷冻和石蜡包埋组织标本，在mRNA和蛋白水平上研究NNGR在原发性结直肠癌、食管癌和胃癌以及匹配的正常组织中的表达。NNGR的结构改变也将被研究，并评估NNGR状态与临床病理特征之间的相关性。对NNGR作用的分子机制也进行了进一步的研究。为此，我们将利用诱导系统将外源NNGR表达到癌细胞中，系统地研究NNGR蛋白的生物学功能。为了研究其结构和功能之间的关系，我们将利用位点定向诱变技术对NNGR的重要基序进行突变，并研究突变对NNGR生物学和生化功能的影响。利用Cre/loxP系统有条件地删除小鼠胃肠道中的NNGR，研究NNGR缺失对胃肠道形态发生和癌变的影响。本提案的长期目标是阐明(1)NNGR在胃肠道恶性肿瘤发病机制中的作用，(2)其作为诊断/预后标志物的地位，无论是单独还是与其他已知标志物联合使用，以及(3)确切的分子作用机制。

A novel gene named NNGR (Novel Negative Growth Regulator) has been cloned. NNGR codes for a secreted protein that harbors two zinc finger-like motifs and exhibits homology to yeast killer toxins. NNGR resides at chromosome 4q21.1-22, a region frequently deleted in esophageal and a subset of colorectal cancers. NNGR expression is either lost or decreased in 5/6 colon, 1/1 gastric and 6/7 of esophageal tumors when compared with their matching normal tissues. Most importantly, NNGR expression in NNGR non-expressing colorectal cancer cells inhibits their growth by inducing apoptosis. Thus, NNGR acts as noel growth suppressor whose expression is either lost or decreased in the primary gastrointestinal (GI) cancers. The proposed studies are aimed at the molecular and functional characterization of NNGR. Specifically, fresh frozen and paraffin-embedded tissue specimens will be utilized to investigate the expression of NNGR at the mRNA and protein levels in primary colorectal, esophageal and gastric cancers and matching normal tissues. Structural alterations in NNGR will also be investigated and a correlation between the NNGR-status and clinicopathological features will be evaluated. Studies are also proposed to elucidate the molecular mechanisms of NNGR action. Towards this end, an inducible system will be used to express exogenous NNGR into cancer cells to systematically study the biological function of the NNGR protein. To investigate the structure function relationships, site-directed mutagenesis will be used to mutate important motifs and the effect of mutations on the biological and biochemical functions of NNGR will be investigated. Cre/loxP system will be used to conditionally delete NNGR in the GI tract of mice and the effects of the absence of NNGR on the GI morphogenesis and carcinogenesis will be investigated. The long-term objectives of this proposal are to elucidate (1) the role of NNGR in pathogenesis of the GI malignancies, (2) its status as a diagnostic/prognostic marker either alone or in combination with other known markers and (3) the exact molecular mechanisms of action.