Digestive Diseases Research Unit, Institut Fundacio Recerca, Hospital General Vall D'hebron, 08035 Barcelona, Spain.
Exp Mol Pathol. 2010 Apr;88(2):272-7. doi: 10.1016/j.yexmp.2009.12.008. Epub 2010 Jan 4.
Osteopontin is thought to play an important role in tumour metastasis. In a previous expression profiling study of murine intestinal adenomas, we found that Opn was up-regulated. We also found beta-catenin binding motifs in the Opn promoter implying that, contrary to current beliefs, induction of Opn may occur during early tumourigenesis. We studied 59 murine intestinal adenomas for Opn expression and every tumour showed up-regulation compared to normal mucosa confirming early deregulation in these tumours. To determine whether Opn makes a functional contribution to tumourigenesis, Opn was knocked down in the murine colorectal cancer cell line CMT93. Inhibition of Opn expression resulted in decreased cell numbers. To determine the mechanism of Opn induction in these tumours, the Opn promoter was cloned and each of the putative beta-catenin binding motifs was mutated. No major change in Opn promoter activity was observed thereby excluding Opn as a direct beta-catenin target gene. However, mutation of one of two putative c-myc binding sites in the Opn promoter led to near complete loss of promoter activity whilst mutation of one of four PEA3 binding sites led to a 50% reduction in promoter activity. We conclude that Opn deregulation is an early event in intestinal tumourigenesis which may promote tumour development by altering either proliferation or apoptosis to increase tumour cell numbers. Opn expression in the intestine is dependent on c-myc binding sites in the promoter. Since c-myc is a known beta-catenin target gene, deregulation of Opn may be a secondary effect of aberrant Wnt signalling.
骨桥蛋白被认为在肿瘤转移中发挥重要作用。在之前对小鼠肠道腺瘤的表达谱研究中，我们发现 Opn 上调。我们还在 Opn 启动子中发现了 β-连环蛋白结合基序，这表明与当前的观点相反，Opn 的诱导可能发生在肿瘤早期发生时。我们研究了 59 个小鼠肠道腺瘤中的 Opn 表达，与正常黏膜相比，每个肿瘤都显示出上调，这证实了这些肿瘤中早期失调。为了确定 Opn 是否对肿瘤发生有功能贡献，我们在小鼠结直肠癌细胞系 CMT93 中敲低了 Opn。Opn 表达的抑制导致细胞数量减少。为了确定这些肿瘤中 Opn 诱导的机制，我们克隆了 Opn 启动子，并对每个假定的 β-连环蛋白结合基序进行了突变。Opn 启动子活性没有观察到明显变化，从而排除了 Opn 作为直接的 β-连环蛋白靶基因。然而，Opn 启动子中两个假定的 c-myc 结合位点中的一个突变导致启动子活性几乎完全丧失，而四个 PEA3 结合位点中的一个突变导致启动子活性降低 50%。我们得出结论，Opn 失调是肠道肿瘤发生的早期事件，它可能通过改变增殖或凋亡来增加肿瘤细胞数量，从而促进肿瘤的发展。肠道中 Opn 的表达依赖于启动子中的 c-myc 结合位点。由于 c-myc 是已知的 β-连环蛋白靶基因，Opn 的失调可能是异常 Wnt 信号的次级效应。
