ヘリコバクター・ピロリ菌感染を起点とする胃癌発症機構の解析

(1)幽门螺杆菌CagA与胃癌的发生作用幽门螺杆菌毒力因子CagA易位到宿主胃上皮细胞后，会被Src家族激酶酪氨酸磷酸化。我们发现酪氨酸磷酸化的CagA蛋白特异性地与SHP-2或Csk结合并解除对催化活性的调节。caga激活的SHP-2引发Erk MAP激酶的持续激活，从而诱导细胞形态转化、细胞运动性升高和细胞生长异常。SHP-2与CagA中含有epiya的区域结合，在东亚和西方CagA中存在显著的序列差异。结果表明，东亚CagA比西方CagA表现出更强的SHP-2结合活性和更高的病理活性。(2) pRB家族肿瘤抑制蛋白的功能与调控。我们发现pRB家族蛋白（pRB， p107和p130）的细胞周期抑制活性共同受到周期蛋白E和周期蛋白d依赖性磷酸化的调控。我们还发现p107在响应DNA损伤的s期细胞生长阻滞中起主要作用。此外，我们发现pRB家族蛋白无论其磷酸化状态如何，都能够转录诱导cyclin D1。(3) ESXR1的分子克隆与分析我们分离到了一个新的人类基因ESXR1，该基因编码一个配对样同源蛋白ESXR1。在细胞中，ESXR1被蛋白水解成一个n端同源结构域片段和一个c端片段。c端片段定位于细胞质并通过抑制m期细胞周期蛋白的降解诱导m期阻滞。另一方面，n端片段定位于细胞核并作为转录抑制因子。通过DNA芯片全基因组筛选，我们确定了K-ras基因是ESXR1的靶基因之一。ESXR1 n端片段的异位表达特异性抑制携带K-ras基因功能获得突变的人类癌细胞的生长。少

(1) Helicobacter pylori CagA and gastric carcinogenesisUpon translocation into host gastric epithelial cells, H. pylori virulence factor CagA undergoes tyrosine phosphorylation by Src family kinases. We found that the tyrosine-phosphorylated CagA protein specifically binds to SHP-2 or Csk and deregulates the catalytic activity. CagA-activated SHP-2 elicited sustained-activation of Erk MAP kinase and thereby induced cell-morphological transformation, elevated cell motility as well as abnormal cell growth. SHP-2 binds to the EPIYA-containing region of CagA, which shows a significant sequence difference between Western and East Asian CagA species. As a result, East Asian CagA species exhibited stronger SHP-2 binding activity and greater pathological activity than Western CagA species.(2) Function and regulation of the pRB family tumor suppressor proteins.We found that the cell cycle-inhibitory activity of the pRB family proteins (pRB, p107 and p130) is collectively regulated by cyclin E a … More nd cyclin D-dependent phosphorylation. We also found that p107 plays a major role in the growth arrest of cells in S-phase in response to DNA damage. Furthermore, we found that pRB family proteins are capable of transcriptionally inducing cyclin D1 regardless of their phosphorylation status.(3) Molecular cloning and analysis of ESXR1We isolated a new human gene, ESXR1, which encodes a paired-like homeoprotein ESXR1. In cells, ESXR1 is proteolytically processed into an N-terminal homeo domain-containing fragment and a C-terminal fragment. The C-terminal fragment localized to the cytoplasm and induced M-phase arrest by inhibiting degradation of M-phase cyclins. On the other hand, the N-terminal fragment localized to the nucleus and acted as a transcriptional repressor. Through genome-wide screening using DNA microarray, we identified the K-ras gene as one of the ESXR1 target genes. Ectopic expression of the ESXR1 N-terminal fragment specifically inhibited growth of human cancer cells that carry gain-of-function mutations in the K-ras gene. Less