microRNA-449a functions as a tumor suppressor in neuroblastoma through inducing cell differentiation and cell cycle arrest

microRNA-449a (miR-449a) has been identified to function as a tumor suppressor in several types of cancers. However, the role of miR-449a in neuroblastoma has not been intensively investigated. We recently found that the overexpression of miR-449a significantly induces neuroblastoma cell differentiation, suggesting its potential tumor suppressor function in neuroblastoma. In this study, we further investigated the mechanisms underlying the tumor suppressive function of miR-449a in neuroblastoma. We observed that miR-449a inhibits neuroblastoma cell survival and growth through 2 mechanisms—inducing cell differentiation and cell cycle arrest. Our comprehensive investigations on the dissection of the target genes of miR-449a revealed that 3 novel targets- MFAP4, PKP4 and TSEN15 -play important roles in mediating its differentiation-inducing function. In addition, we further found that its function in inducing cell cycle arrest involves down-regulating its direct targets CDK6 and LEF1. To determine the clinical significance of the miR-449a-mediated tumor suppressive mechanism, we examined the correlation between the expression of these 5 target genes in neuroblastoma tumor specimens and the survival of neuroblastoma patients. Remarkably, we noted that high tumor expression levels of all the 3 miR-449a target genes involved in regulating cell differentiation, but not the target genes involved in regulating cell cycle, are significantly correlated with poor survival of neuroblastoma patients. These results suggest the critical role of the differentiation-inducing function of miR-449a in determining neuroblastoma progression. Overall, our study provides the first comprehensive characterization of the tumor-suppressive function of miR-449a in neuroblastoma, and reveals the potential clinical significance of the miR-449a-mediated tumor suppressive pathway in neuroblastoma prognosis.

微RNA-449a（miR-449a）已被确认为多种癌症中的肿瘤抑制因子。然而，miR-449a在神经母细胞瘤中的作用尚未得到深入研究。我们近期发现，miR-449a的高表达显著诱导神经母细胞瘤细胞的分化，提示其在神经母细胞瘤中可能具有肿瘤抑制功能。在本研究中，我们进一步探讨了miR-449a在神经母细胞瘤中肿瘤抑制功能的分子机制。我们发现，miR-449a通过诱导细胞分化和细胞周期停滞两种机制抑制神经母细胞瘤细胞的存活和生长。我们对miR-449a靶基因的深入解析揭示了三个新型靶点——MFAP4、PKP4和TSEN15，它们在介导其分化诱导功能中发挥重要作用。此外，我们还发现，其诱导细胞周期停滞的功能涉及下调其直接靶标CDK6和LEF1。为了确定miR-449a介导的肿瘤抑制机制的临床意义，我们考察了这五个靶基因（包括调节细胞分化的三个靶基因和调节细胞周期的靶基因）在神经母细胞瘤肿瘤标本中的表达与神经母细胞瘤患者生存率之间的相关性。值得注意的是，我们发现所有三个参与调节细胞分化的miR-449a靶基因的高肿瘤表达水平与神经母细胞瘤患者的生存率较差显著相关，而与调节细胞周期的靶基因无关。这些结果提示miR-449a的分化诱导功能在决定神经母细胞瘤进展中的关键作用。总体而言，我们的研究首次对miR-449a在神经母细胞瘤中的肿瘤抑制功能进行了全面描述，并揭示了miR-449a介导的肿瘤抑制通路在神经母细胞瘤预后中的潜在临床意义。