Department of Cancer Biology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 2013 Sep 3;110(36):14520-7. doi: 10.1073/pnas.1308610110. Epub 2013 Aug 5.
An immature state of cellular differentiation--characterized by stem cell-like tendencies and impaired differentiation--is a hallmark of cancer. Using glioblastoma multiforme (GBM) as a model system, we sought to determine whether molecular determinants that drive cells toward terminal differentiation are also genetically targeted in carcinogenesis and whether neutralizing such genes also plays an active role to reinforce the impaired differentiation state and promote malignancy. To that end, we screened 71 genes with known roles in promoting nervous system development that also sustain copy number loss in GBM through antineoplastic assay and identified A2BP1 (ataxin 2 binding protein 1, Rbfox1), an RNA-binding and splicing regulator that is deleted in 10% of GBM cases. Integrated in silico analysis of GBM profiles to elucidate the A2BP1 pathway and its role in glioma identified myelin transcription factor 1-like (Myt1L) as a direct transcriptional regulator of A2BP1. Reintroduction of A2BP1 or Myt1L in GBM cell lines and glioma stem cells profoundly inhibited tumorigenesis in multiple assays, and conversely, shRNA-mediated knockdown of A2BP1 or Myt1L in premalignant neural stem cells compromised neuronal lineage differentiation and promoted orthotopic tumor formation. On the mechanistic level, with the top-represented downstream target TPM1 as an illustrative example, we demonstrated that, among its multiple functions, A2BP1 serves to regulate TPM1's alternative splicing to promote cytoskeletal organization and terminal differentiation and suppress malignancy. Thus, in addition to the activation of self-renewal pathways, the neutralization of genetic programs that drive cells toward terminal differentiation may also promote immature and highly plastic developmental states that contribute to the aggressive malignant properties of GBM.
细胞分化不成熟的状态——其特征为具有干细胞样倾向和分化受损——是癌症的一个标志。我们使用多形性成胶质细胞瘤 (GBM) 作为模型系统，试图确定促使细胞向终末分化的分子决定因素是否也在致癌作用中受到遗传靶向，以及中和这些基因是否也起到积极作用，以加强受损的分化状态并促进恶性肿瘤。为此，我们通过抗肿瘤测定筛选了 71 个已知在促进神经系统发育中起作用的基因，这些基因在 GBM 中也维持着拷贝数缺失，并鉴定出 A2BP1（ataxin 2 结合蛋白 1，Rbfox1），这是一种 RNA 结合和剪接调节因子，在 10%的 GBM 病例中缺失。通过对 GBM 图谱进行综合的计算机分析，以阐明 A2BP1 通路及其在神经胶质瘤中的作用，确定少突胶质细胞转录因子 1 样（Myt1L）是 A2BP1 的直接转录调节因子。在 GBM 细胞系和神经胶质瘤干细胞中重新引入 A2BP1 或 Myt1L，在多种检测中均显著抑制了肿瘤发生，相反，在前期神经干细胞中用 shRNA 介导的 A2BP1 或 Myt1L 敲低，损害了神经元谱系分化并促进了原位肿瘤形成。在机制水平上，以代表性最强的下游靶标 TPM1 为例，我们证明，除了其多种功能外，A2BP1 还可调节 TPM1 的可变剪接，以促进细胞骨架组织和终末分化，并抑制恶性肿瘤。因此，除了激活自我更新途径外，中和促使细胞向终末分化的遗传程序也可能促进不成熟和高度可塑性的发育状态，这有助于 GBM 的侵袭性恶性特性。
