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 two mechanisms — inducing cell differentiation and cell cycle arrest. Our comprehensive investigations on the dissection of the target genes of miR-449a revealed that three 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 five target genes in neuroblastoma tumor specimens and the survival of neuroblastoma patients. Remarkably, we noted that high tumor expression levels of all the three 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.

miR-449a（微RNA-449a）已被确认为多种癌症中的抑癌基因。然而，其在神经母细胞瘤中的功能尚未得到深入研究。近期，我们研究发现miR-449a的高表达显著诱导神经母细胞瘤细胞的分化，暗示其在神经母细胞瘤中可能具有抑癌功能。在本研究中，我们进一步探讨了miR-449a在神经母细胞瘤中抑癌功能背后的机制。我们发现miR-449a通过两种机制抑制神经母细胞瘤细胞的存活和生长——诱导细胞分化和细胞周期阻滞。我们对miR-449a靶基因的解析研究全面揭示了三个新型靶基因——MFAP4、PKP4和TSEN15——在介导其分化诱导功能中发挥着重要作用。此外，我们还发现其在诱导细胞周期阻滞中的作用涉及下调其直接靶基因CDK6和LEF1的表达。为确定miR-449a介导的抑癌机制的临床意义，我们考察了神经母细胞瘤肿瘤标本中这五个靶基因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，与调节细胞周期的靶基因相比，参与调节细胞分化的三个miR-449a靶基因的高肿瘤表达水平与神经母细胞瘤患者的不良预后显著相关。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。总的来说，我们的研究首次全面描述了miR-449a在神经母细胞瘤中的抑癌功能，并揭示了miR-449a介导的抑癌途径在神经母细胞瘤预后中的潜在临床意义。