Miyaki M, Iijima T, Konishi M, Sakai K, Ishii A, Yasuno M, Hishima T, Koike M, Shitara N, Iwama T, Utsunomiya J, Kuroki T, Mori T
Hereditary Tumor Research Project, The Tokyo Metropolitan Komagome Hospital, Japan.
Oncogene. 1999 May 20;18(20):3098-103. doi: 10.1038/sj.onc.1202642.
We have previously detected an increased frequency of loss of heterozygosity (LOH) on chromosome 18q during progression of colorectal carcinomas. To clarify the target of 18qLOH, mutation of Smad4 and Smad2 genes was analysed in 176 colorectal tumors with different stages, including liver metastasis, from 111 sporadic, 52 familial adenomatous polyposis (FAP) and nine hereditary nonpolyposis colorectal cancer (HNPCC) patients. Mutation of other Smad gene families in the TGF-beta signaling pathway was also examined. Twenty-one Smad4 mutations and one Smad2 mutation were detected, whereas mutation of Smad3, 6 and 7 genes was not detected. Smad4 mutations included seven frameshift, one inframe deletion, four nonsense and nine missense mutations, 95% of which resulted in alteration of Smad4 protein regions included in homo-oligomer and hetero-oligomer formation. Frequencies of tumors with Smad4 mutation were 0/40 (0%) in adenoma, 4/39 (10%) in intramucosal carcinoma, 3/44 (7%) in primary invasive carcinoma without distant metastasis, 6/17 (35%) in primary invasive carcinoma with distant metastasis, and 11/36 (31%) in distant metastasis (metastatic/non-metastatic: P=0.006 approximately 0.01). Loss of the other allele was observed in 19 of 20 (95%) invasive and metastasized carcinomas with Smad4 mutations. In four cases both primary and metastasized carcinomas in the same patients showed the same mutations. The present results suggest that Smad4 gene is one of true targets of 18qLOH, and that its inactivation is involved in advanced stages, such as distant metastasis, in human colorectal carcinogenesis.
我们之前检测到在结直肠癌进展过程中18号染色体长臂杂合性缺失（LOH）的频率增加。为了明确18qLOH的靶点，我们分析了176例不同分期（包括肝转移）的结直肠肿瘤中Smad4和Smad2基因的突变情况，这些肿瘤来自111例散发性、52例家族性腺瘤性息肉病（FAP）和9例遗传性非息肉病性结直肠癌（HNPCC）患者。我们还检测了TGF-β信号通路中其他Smad基因家族的突变。检测到21例Smad4突变和1例Smad2突变，而未检测到Smad3、6和7基因的突变。Smad4突变包括7例移码突变、1例框内缺失、4例无义突变和9例错义突变，其中95%导致Smad4蛋白中参与同源寡聚体和异源寡聚体形成的区域发生改变。腺瘤中Smad4突变肿瘤的频率为0/40（0%），黏膜内癌为4/39（10%），无远处转移的原发性浸润癌为3/44（7%），有远处转移的原发性浸润癌为6/17（35%），远处转移灶为11/36（31%）（转移灶/非转移灶：P = 0.006至0.01）。在20例有Smad4突变的浸润性和转移性癌中，有19例（95%）观察到另一个等位基因的缺失。在4例患者中，同一患者的原发性和转移性癌均显示相同的突变。目前的结果表明，Smad4基因是18qLOH的真正靶点之一，其失活参与了人类结直肠癌发生的晚期阶段，如远处转移。
