Isler Silvia G, Ludwig Christian U, Chiquet-Ehrismann Ruth, Schenk Susanne
Friedrich Miescher Institute, Novartis Research Foundation, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.
Int J Oncol. 2004 Oct;25(4):1073-9.
SPARCL1 mRNA was shown to be downregulated in NSCLC as well as in prostate, colon, and bladder carcinomas. Therefore, SPARCL1 was suggested to be a tumor suppressor gene. By microsatellite analysis, real-time quantitative PCR, and sequence analysis of all exons including the intron-exon junctions and a part of the putative promoter region, we could not find any deletion or mutation that might be responsible for the downregulation of SPARCL1 in NSCLC. We conclude that SPARCL1 is therefore not a classical tumor suppressor gene with a deletion or mutation in one allele and another mutation in the second allele. To test whether SPARCL1 could be downregulated by repression of transcription we performed luciferase reporter gene assays with 10 different SPARCL1 promoter constructs. These experiments revealed that the presence of exon 1 is able to cause a reduction in luciferase activity. Furthermore, we show that the inhibitory activity of exon 1 can be transferred to a heterologous promoter. This indicates that SPARCL1 downregulation might be mediated (at least in part) through transacting factors that bind to exon 1.
SPARCL1信使核糖核酸在非小细胞肺癌以及前列腺癌、结肠癌和膀胱癌中均呈下调状态。因此，SPARCL1被认为是一种肿瘤抑制基因。通过微卫星分析、实时定量聚合酶链反应以及对包括内含子 - 外显子连接区和部分假定启动子区域在内的所有外显子进行序列分析，我们在非小细胞肺癌中未发现任何可能导致SPARCL1下调的缺失或突变。我们得出结论，因此SPARCL1不是一个经典的肿瘤抑制基因，即一个等位基因存在缺失或突变而另一个等位基因存在另一种突变的情况。为了测试SPARCL1是否可能通过转录抑制而下调，我们用10种不同的SPARCL1启动子构建体进行了荧光素酶报告基因检测。这些实验表明，外显子1的存在能够导致荧光素酶活性降低。此外，我们表明外显子1的抑制活性可以转移到异源启动子上。这表明SPARCL1的下调可能（至少部分）是通过与外显子1结合的反式作用因子介导的。
