Kuramochi M, Fukuhara H, Nobukuni T, Kanbe T, Maruyama T, Ghosh H P, Pletcher M, Isomura M, Onizuka M, Kitamura T, Sekiya T, Reeves R H, Murakami Y
Tumor Suppression & Functional Genomics Project, National Cancer Center Research Institute, Tokyo, Japan.
Nat Genet. 2001 Apr;27(4):427-30. doi: 10.1038/86934.
The existence of tumor-suppressor genes was originally demonstrated by functional complementation through whole-cell and microcell fusion. Transfer of chromosome 11 into a human non-small-cell lung cancer (NSCLC) cell line, A549, suppresses tumorigenicity. Loss of heterozygosity (LOH) on the long arm of chromosome 11 has been reported in NSCLC and other cancers. Several independent studies indicate that multiple tumor-suppressor genes are found in this region, including the gene PPP2R1B at 11q23-24 (ref. 7). Linkage studies of NSCLC are precluded because no hereditary forms are known. We previously identified a region of 700 kb on 11q23.2 that completely suppresses tumorigenicity of A549 human NSCLC cells. Most of this tumor-suppressor activity localizes to a 100-kb segment by functional complementation. Here we report that this region contains a single confirmed gene, TSLC1, whose expression is reduced or absent in A549 and several other NSCLC, hepatocellular carcinoma (HCC) and pancreatic cancer (PaC) cell lines. TSLC1 expression or suppression is correlated with promoter methylation state in these cell lines. Restoration of TSLC1 expression to normal or higher levels suppresses tumor formation by A549 cells in nude mice. Only 2 inactivating mutations of TSLC1 were discovered in 161 tumors and tumor cell lines, both among the 20 primary tumors with LOH for 11q23.2. Promoter methylation was observed in 15 of the other 18 primary NSCLC, HCC and PaC tumors with LOH for 11q23.2. Thus, attenuation of TSLC1 expression occurred in 85% of primary tumors with LOH. Hypermethylation of the TSLC1 promoter would seem to represent the 'second hit' in NSCLC with LOH.
肿瘤抑制基因的存在最初是通过全细胞和微细胞融合的功能互补来证明的。将11号染色体转移到人非小细胞肺癌（NSCLC）细胞系A549中可抑制致瘤性。在NSCLC和其他癌症中已报道11号染色体长臂上存在杂合性缺失（LOH）。多项独立研究表明，该区域存在多个肿瘤抑制基因，包括位于11q23 - 24的PPP2R1B基因（参考文献7）。由于未知遗传性形式，NSCLC的连锁研究受到限制。我们之前在11q23.2上鉴定出一个700 kb的区域，该区域可完全抑制A549人NSCLC细胞的致瘤性。通过功能互补，大部分这种肿瘤抑制活性定位于一个100 kb的片段。在此我们报告，该区域包含一个单一的已证实基因TSLC1，其在A549以及其他几种NSCLC、肝细胞癌（HCC）和胰腺癌（PaC）细胞系中的表达降低或缺失。在这些细胞系中，TSLC1的表达或抑制与启动子甲基化状态相关。将TSLC1表达恢复到正常或更高水平可抑制A549细胞在裸鼠体内形成肿瘤。在161个肿瘤和肿瘤细胞系中仅发现2个TSLC1的失活突变，且均在20个11q23.2存在LOH的原发性肿瘤中。在另外18个11q23.2存在LOH的原发性NSCLC、HCC和PaC肿瘤中，有15个观察到启动子甲基化。因此，在85%的11q23.2存在LOH的原发性肿瘤中发生了TSLC1表达减弱。TSLC1启动子的高甲基化似乎代表了11q23.2存在LOH的NSCLC中的“二次打击”。
