Wu W, Kemp B L, Proctor M L, Gazdar A F, Minna J D, Hong W K, Mao L
Department of Thoracic/Head and Neck Medical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Cancer Res. 1999 Apr 15;59(8):1846-51.
DMBT1 is a candidate tumor suppressor gene located at 10q25.3-26.1. Homozygous deletion of the gene was found in a subset of medulloblastoma and glioblastoma multiforme; lack of expression was noted in the majority of these tumors. In adult tissues, DMBT1 is highly expressed only in lung and small intestine tissues, indicating its important role in these organs. By analyzing lung cancer cell lines and primary lung tumors using reverse transcription-PCR, we found that 100% (20 of 20) of small cell lung cancer (SCLC) cell lines and 43% (6 of 14) of non-small cell lung cancer (NSCLC) cell lines lacked DMBT1 expression. Furthermore, 45% (9 of 20) of the primary NSCLCs exhibited a markedly low level of gene expression compared with corresponding normal lung tissues, indicating that lack of gene expression also occurs in primary lung cancers. To determine the potential mechanisms for lack of DMBT1 expression in lung cancer, we analyzed tumor cell lines for potential intragenic homozygous deletions of the gene and found such homozygous deletions in 10% (4 of 40) of SCLC cell lines but in none of 14 NSCLC cell lines. Moreover, the loss of expression could not be rescued by treatment with a demethylation agent (5-azacytidine) in two NSCLC cell lines lacking DMBT1 expression, suggesting that de novo methylation of the promoter region of the gene is unlikely to play a role in inactivation of the gene. We then sequenced the whole coding region of DMBT1 in 8 NSCLC cell lines that expressed DMBT1 and 20 primary NSCLCs. A potential point mutation at codon 52 was detected in a NSCLC cell line and resulted in an amino acid change from serine to tryptophan. Three common polymorphisms were also detected in tissues analyzed. Our data demonstrate that DMBT1 expression is frequently lost in lung cancer due to gene deletion and to other not yet identified mechanisms, suggesting that inactivation of DMBT1 may play an important role in lung tumorigenesis.
DMBT1是一个位于10q25.3 - 26.1的候选抑癌基因。在一部分髓母细胞瘤和多形性胶质母细胞瘤中发现了该基因的纯合缺失；在这些肿瘤的大多数中都观察到表达缺失。在成人组织中，DMBT1仅在肺和小肠组织中高表达，表明其在这些器官中起重要作用。通过逆转录 - PCR分析肺癌细胞系和原发性肺肿瘤，我们发现100%（20/20）的小细胞肺癌（SCLC）细胞系和43%（6/14）的非小细胞肺癌（NSCLC）细胞系缺乏DMBT1表达。此外，与相应的正常肺组织相比，45%（9/20）的原发性NSCLC表现出明显低水平的基因表达，表明原发性肺癌中也存在基因表达缺失。为了确定肺癌中DMBT1表达缺失的潜在机制，我们分析了肿瘤细胞系中该基因潜在的基因内纯合缺失，在10%（4/40）的SCLC细胞系中发现了这种纯合缺失，但在14个NSCLC细胞系中均未发现。此外，在两个缺乏DMBT1表达的NSCLC细胞系中，用去甲基化剂（5 - 氮杂胞苷）处理并不能挽救表达缺失，这表明该基因启动子区域的从头甲基化不太可能在基因失活中起作用。然后我们对8个表达DMBT1的NSCLC细胞系和20个原发性NSCLC的DMBT1全编码区进行了测序。在一个NSCLC细胞系中检测到密码子52处的一个潜在点突变，导致氨基酸从丝氨酸变为色氨酸。在分析的组织中还检测到了三种常见的多态性。我们的数据表明，由于基因缺失和其他尚未确定的机制，DMBT1表达在肺癌中经常丧失，这表明DMBT1的失活可能在肺肿瘤发生中起重要作用。
