Coda Davide Martino, Lingua Marcello Francesco, Morena Deborah, Foglizzo Valentina, Bersani Francesca, Ala Ugo, Ponzetto Carola, Taulli Riccardo
a Department of Oncology ; University of Turin ; Turin , Italy.
Cell Cycle. 2015;14(9):1389-402. doi: 10.1080/15384101.2015.1005993.
Rhadomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood. RMS cells resemble fetal myoblasts but are unable to complete myogenic differentiation. In previous work we showed that miR-206, which is low in RMS, when induced in RMS cells promotes the resumption of differentiation by modulating more than 700 genes. To better define the pathways involved in the conversion of RMS cells into their differentiated counterpart, we focused on 2 miR-206 effectors emerged from the microarray analysis, SMYD1 and G6PD. SMYD1, one of the most highly upregulated genes, is a H3K4 histone methyltransferase. Here we show that SMYD1 silencing does not interfere with the proliferative block or with the loss anchorage independence imposed by miR-206, but severely impairs differentiation of ERMS, ARMS, and myogenic cells. Thus SMYD1 is essential for the activation of muscle genes. Conversely, among the downregulated genes, we found G6PD, the enzyme catalyzing the rate-limiting step of the pentose phosphate shunt. In this work, we confirmed that G6PD is a direct target of miR-206. Moreover, we showed that G6PD silencing in ERMS cells impairs proliferation and soft agar growth. However, G6PD overexpression does not interfere with the pro-differentiating effect of miR-206, suggesting that G6PD downmodulation contributes to - but is not an absolute requirement for - the tumor suppressive potential of miR-206. Targeting cancer metabolism may enhance differentiation. However, therapeutic inhibition of G6PD is encumbered by side effects. As an alternative, we used DCA in combination with miR-206 to increase the flux of pyruvate into the mitochondrion by reactivating PDH. DCA enhanced the inhibition of RMS cell growth induced by miR-206, and sustained it upon miR-206 de-induction. Altogether these results link miR-206 to epigenetic and metabolic reprogramming, and suggest that it may be worth combining differentiation-inducing with metabolism-directed approaches.
横纹肌肉瘤（RMS）是儿童期最常见的软组织肉瘤。RMS细胞类似于胎儿成肌细胞，但无法完成肌源性分化。在之前的研究中，我们发现RMS中低表达的miR-206，在RMS细胞中诱导表达时，通过调控700多个基因促进分化的恢复。为了更好地确定RMS细胞转化为分化对应细胞所涉及的途径，我们聚焦于微阵列分析中出现的2个miR-206效应分子，即SMYD1和G6PD。SMYD1是上调程度最高的基因之一，是一种H3K4组蛋白甲基转移酶。在此我们表明，SMYD1沉默并不干扰miR-206所导致的增殖阻滞或失去锚定非依赖性，但严重损害胚胎型RMS（ERMS）、腺泡型RMS（ARMS）和成肌细胞的分化。因此，SMYD1对于肌肉基因的激活至关重要。相反，在下调基因中，我们发现了G6PD，它是催化磷酸戊糖途径限速步骤的酶。在这项研究中，我们证实G6PD是miR-206的直接靶点。此外，我们表明在ERMS细胞中沉默G6PD会损害细胞增殖和软琼脂生长。然而，G6PD过表达并不干扰miR-206的促分化作用，这表明G6PD下调有助于但不是miR-206肿瘤抑制潜能的绝对必要条件。靶向癌症代谢可能会增强分化。然而，G6PD的治疗性抑制受到副作用的限制。作为替代方案，我们使用二氯乙酸（DCA）与miR-206联合使用，通过重新激活丙酮酸脱氢酶（PDH）来增加丙酮酸进入线粒体的通量。DCA增强了miR-206对RMS细胞生长的抑制作用，并在miR-206去诱导后持续存在。总之，这些结果将miR-206与表观遗传和代谢重编程联系起来，并表明将诱导分化与代谢导向方法相结合可能是值得的。
