A MYCN-independent mechanism mediating secretome reprogramming and metastasis in MYCN-amplified neuroblastoma

MYCN amplification (MNA) is a defining feature of high-risk neuroblastoma (NB) that predicts poor prognosis. However, whether genes within or in close proximity to the MYCN amplicon also contribute to aggressiveness in MNA+ NB remains poorly understood. Here we identify that GREB1, a transcription factor encoding gene neighboring the MYCN locus, is frequently co-expressed with MYCN, and promotes cell survival in MNA+ NB. GREB1 controls gene expression independently of MYCN in MNA+ NB, among which we uncover Myosin 1B (MYO1B) as being highly expressed in MNA+ NB. MYO1B promotes aggressive features, including invasive capacity in vitro, as well as extravasation and distant metastasis in vivo. Global secretome and proteome profiling further delineate MYO1B as a major regulator of secretome reprogramming in MNA+ NB cells. Moreover, we identify the cytokine MIF as an important pro-invasive and pro-metastatic mediator of MYO1B activity. Together, we have identified a putative GREB1-MYO1B-MIF axis as an unconventional mechanism that promotes the aggressiveness of MNA+ NB, and independently of MYCN. Furthermore, we find that MYO1B is upregulated in association with other oncoproteins during cellular transformation, and is dramatically increased in multiple human cancer types, suggesting a crucial role of MYO1B in cancers in addition to MNA+ NB.

MYCN扩增（MYCN amplification, MNA）是高危神经母细胞瘤（neuroblastoma, NB）的标志性特征，可提示不良预后。然而，MYCN扩增区域内或邻近区域的基因是否也会促进MNA阳性（MNA+）神经母细胞瘤的侵袭性，目前仍知之甚少。本研究鉴定发现，定位于MYCN基因座邻近区域的转录因子编码基因GREB1常与MYCN共表达，并可促进MNA+神经母细胞瘤的细胞存活。在MNA+神经母细胞瘤中，GREB1可独立于MYCN调控基因表达，其中我们发现肌球蛋白1B（Myosin 1B, MYO1B）在MNA+神经母细胞瘤中呈高表达。MYO1B可促进多种侵袭性表型，包括体外侵袭能力，以及体内血管外渗和远处转移。全局分泌组与蛋白质组分析进一步证实，MYO1B是MNA+神经母细胞瘤细胞分泌组重编程的主要调控因子。此外，我们鉴定发现细胞因子MIF是介导MYO1B发挥促侵袭与促转移活性的重要因子。综上，本研究鉴定出一条非依赖MYCN的、可促进MNA+神经母细胞瘤侵袭性的潜在GREB1-MYO1B-MIF信号轴。进一步研究发现，在细胞转化过程中，MYO1B的表达上调与其他癌蛋白密切相关，且在多种人类癌症类型中均显著升高，这提示MYO1B除在MNA+神经母细胞瘤中发挥关键作用外，在其他癌症中也具有重要的调控功能。