Aström A K, Voz M L, Kas K, Röijer E, Wedell B, Mandahl N, Van de Ven W, Mark J, Stenman G
Department of Pathology, Göteborg University, Sweden.
Cancer Res. 1999 Feb 15;59(4):918-23.
We have previously shown (K. Kas et al, Nat. Genet., 15: 170-174, 1997) that the developmentally regulated zinc finger gene pleomorphic adenoma gene 1 (PLAG1) is the target gene in 8q12 in pleomorphic adenomas of the salivary glands with t(3;8)(p21;q12) translocations. The t(3;8) results in promoter swapping between PLAG1 and the constitutively expressed gene for beta-catenin (CTNNB1), leading to activation of PLAG1 expression and reduced expression of CTNNB1. Here we have studied the expression of PLAG1 by Northern blot analysis in 47 primary benign and malignant human tumors with or without cytogenetic abnormalities of 8q12. Overexpression of PLAG1 was found in 23 tumors (49%). Thirteen of 17 pleomorphic adenomas with a normal karyotype and 5 of 10 with 12q13-15 abnormalities overexpressed PLAG1, which demonstrates that PLAG1 activation is a frequent event in adenomas irrespective of karyotype. In contrast, PLAG1 was overexpressed in only 2 of 11 malignant salivary gland tumors analyzed, which suggests that, at least in salivary gland tumors, PLAG1 activation preferentially occurs in benign tumors. PLAG1 over-expression was also found in three of nine mesenchymal tumors, i.e., in two uterine leiomyomas and one leiomyosarcoma. RNase protection, rapid amplification of 5'-cDNA ends (5'-RACE), and reverse transcription-PCR analyses of five adenomas with a normal karyotype revealed fusion transcripts in three tumors. Nucleotide sequence analysis of these showed that they contained fusions between PLAG1 and CTNNB1 (one case) or PLAG1 and a novel fusion partner gene, i.e., the gene encoding the transcription elongation factor SII (two cases). The fusions occurred in the 5' noncoding region of PLAG1, leading to exchange of regulatory control elements and, as a consequence, activation of PLAG1 gene expression. Because all of the cases had grossly normal karyotypes, the rearrangements must result from cryptic rearrangements. The results suggest that in addition to chromosomal translocations and cryptic rearrangements, PLAG1 may also be activated by mutations or indirect mechanisms. Our findings establish a conserved mechanism of PLAG1 activation in salivary gland tumors with and without 8q12 aberrations, which indicates that such activation is a frequent event in these tumors.
我们之前已经表明（K. Kas等人，《自然遗传学》，15: 170 - 174, 1997），发育调控的锌指基因多形性腺瘤基因1（PLAG1）是唾液腺多形性腺瘤中t(3;8)(p21;q12)易位时8q12区域的靶基因。t(3;8)易位导致PLAG1与β - 连环蛋白（CTNNB1）的组成型表达基因之间发生启动子交换，从而导致PLAG1表达激活以及CTNNB1表达降低。在此，我们通过Northern印迹分析研究了47例有或无8q12细胞遗传学异常的原发性人类良恶性肿瘤中PLAG1的表达情况。在23例肿瘤（49%）中发现了PLAG1的过表达。17例核型正常的多形性腺瘤中有13例以及10例有12q13 - 15异常的多形性腺瘤中有5例过表达PLAG1，这表明无论核型如何，PLAG1激活在腺瘤中都是常见事件。相比之下，在分析的11例恶性唾液腺肿瘤中只有2例PLAG1过表达，这表明至少在唾液腺肿瘤中，PLAG1激活优先发生在良性肿瘤中。在9例间叶组织肿瘤中的3例，即2例子宫平滑肌瘤和1例平滑肌肉瘤中也发现了PLAG1过表达。对5例核型正常的腺瘤进行核糖核酸酶保护、5' - cDNA末端快速扩增（5' - RACE）以及逆转录 - PCR分析，在3例肿瘤中发现了融合转录本。对这些转录本的核苷酸序列分析表明，它们包含PLAG1与CTNNB1之间的融合（1例）或PLAG1与一个新的融合伙伴基因，即编码转录延伸因子SII的基因之间的融合（2例）。融合发生在PLAG1的5'非编码区，导致调控元件交换，从而激活PLAG1基因表达。由于所有这些病例的核型大体正常，这种重排必定是由隐匿性重排导致的。结果表明，除了染色体易位和隐匿性重排外，PLAG1也可能通过突变或间接机制被激活。我们的研究结果确立了在有或无8q12畸变的唾液腺肿瘤中PLAG1激活的保守机制，这表明这种激活在这些肿瘤中是常见事件。
