Komiya T, Park Y, Modi S, Coxon A B, Oh H, Kaye F J
Genetics Branch, Center for Cancer Research, National Cancer Institute and National Naval Medical Center, Bethesda, MD, USA.
Oncogene. 2006 Oct 5;25(45):6128-32. doi: 10.1038/sj.onc.1209627. Epub 2006 May 1.
Mucoepidermoid (MEC) salivary gland tumors arise from a t(11;19) rearrangement which generates a fusion oncogene, Mect1-Maml2, that functions to activate CREB-responsive target genes. To determine if sustained expression of Mect1-Maml2 is required for tumor cell growth, we first showed that ectopic expression of Mect1-Maml2 in rat epithelial RK3E cells is tumorigenic in vivo in nude mice and that excised xenografts continue to express the fusion oncogene. We then generated a hairpin RNAi vector that selectively suppressed the fusion peptide and showed that ectopic expression in either parotid or pulmonary MEC tumor cell lines containing the t(11;19) rearrangement resulted in at least 90% colony growth inhibition. In contrast, single nucleotide changes within this RNAi sequence abolished the ability to suppress Mect1-Maml2 protein and abolished all growth inhibition of these MEC tumor lines. In addition, the RNAi-specific vector had no effect on colony growth of non-MEC tumors including a lung tumor or two other salivary gland cell lines that do not express Mect1-Maml2. We also generated a mutant Mect1-Maml2 expression plasmid that carried silent nucleotide changes within the RNAi target sequence and observed that co-transfection of this mutant, but not wild-type Mect1-Maml2, could partially rescue RNAi growth inhibition in the MEC tumor line. The recent detection of acquired fusion oncogenes in epithelial solid tumors has suggested new possibilities for the diagnosis and therapy of these cancers. Our data show that the 'gain-of-function' activity from aberrant Mect1-Maml2 expression is a candidate therapeutic target for this group of malignant salivary gland tumors.
黏液表皮样（MEC）唾液腺肿瘤由t(11;19)重排产生，该重排产生一种融合癌基因Mect1-Maml2，其作用是激活CREB反应性靶基因。为了确定肿瘤细胞生长是否需要Mect1-Maml2的持续表达，我们首先表明，在大鼠上皮RK3E细胞中异位表达Mect1-Maml2在裸鼠体内具有致瘤性，切除的异种移植物继续表达融合癌基因。然后，我们构建了一个选择性抑制融合肽的发夹RNAi载体，结果表明，在含有t(11;19)重排的腮腺或肺MEC肿瘤细胞系中异位表达该载体，可导致至少90%的集落生长抑制。相比之下，该RNAi序列内的单核苷酸变化消除了抑制Mect1-Maml2蛋白的能力，并消除了对这些MEC肿瘤细胞系的所有生长抑制作用。此外，RNAi特异性载体对包括肺癌或另外两个不表达Mect1-Maml2的唾液腺细胞系在内的非MEC肿瘤的集落生长没有影响。我们还构建了一个在RNAi靶序列内携带沉默核苷酸变化的突变型Mect1-Maml2表达质粒，并观察到共转染该突变体（而非野生型Mect1-Maml2）可部分挽救MEC肿瘤细胞系中RNAi介导的生长抑制。最近在上皮性实体瘤中检测到获得性融合癌基因，为这些癌症的诊断和治疗提供了新的可能性。我们的数据表明，异常的Mect1-Maml2表达产生的“功能获得”活性是这组恶性唾液腺肿瘤的一个候选治疗靶点。
