Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel.
Oncogene. 2013 Jul 4;32(27):3220-30. doi: 10.1038/onc.2012.340. Epub 2012 Aug 6.
L1, a neuronal cell adhesion receptor of the immunoglobulin-like protein family is expressed in invading colorectal cancer (CRC) cells as a target gene of Wnt/β-catenin signaling. Overexpression of L1 in CRC cells enhances cell motility and proliferation, and confers liver metastasis. We recently identified ezrin and the IκB-NF-κB pathway as essential for the biological properties conferred by L1 in CRC cells. Here, we studied the underlying molecular mechanisms and found that L1 enhances ezrin phosphorylation, via Rho-associated protein kinase (ROCK), and is required for L1-ezrin co-localization at the juxtamembrane domain and for enhancing cell motility. Global transcriptomes from L1-expressing CRC cells were compared with transcriptomes from the same cells expressing small hairpin RNA (shRNA) to ezrin. Among the genes whose expression was elevated by L1 and ezrin we identified insulin-like growth factor-binding protein 2 (IGFBP-2) and showed that its increased expression is mediated by an NF-κB-mediated transactivation of the IGFBP-2 gene promoter. Expression of a constitutively activated mutant ezrin (Ezrin567D) could also increase IGFBP-2 levels in CRC cells. Overexpression of IGFBP-2 in CRC cells lacking L1-enhanced cell proliferation (in the absence of serum), cell motility, tumorigenesis and induced liver metastasis, similar to L1 overexpression. Suppression of endogenous IGFBP-2 in L1-transfected cells inhibited these properties conferred by L1. We detected IGFBP-2 in a unique organization at the bottom of human colonic crypts in normal mucosa and at increased levels throughout human CRC tissue samples co-localizing with the phosphorylated p65 subunit of NF-κB. Finally, we found that IGFBP-2 and L1 can form a molecular complex suggesting that L1-mediated signaling by the L1-ezrin-NF-κB pathway, that induces IGFBP-2 expression, has an important role in CRC progression.
L1 是免疫球蛋白样蛋白家族的一种神经元细胞粘附受体，作为 Wnt/β-catenin 信号的靶基因在侵袭性结直肠癌 (CRC) 细胞中表达。CRC 细胞中 L1 的过表达增强了细胞的迁移和增殖能力，并赋予了肝转移的能力。我们最近确定了 ezrin 和 IκB-NF-κB 途径是 L1 在 CRC 细胞中赋予这些生物学特性所必需的。在这里，我们研究了潜在的分子机制，发现 L1 通过 Rho 相关蛋白激酶 (ROCK) 增强 ezrin 的磷酸化，并需要 L1-ezrin 在质膜附近区域的共定位以及增强细胞迁移。与表达小发夹 RNA (shRNA) 到 ezrin 的相同细胞的转录组进行比较，从表达 L1 的 CRC 细胞中获得了全局转录组。在 L1 和 ezrin 上调的基因中，我们鉴定出胰岛素样生长因子结合蛋白 2 (IGFBP-2)，并表明其表达增加是由 IGFBP-2 基因启动子的 NF-κB 介导的转录激活介导的。组成型激活突变体 ezrin (Ezrin567D) 的表达也可以增加 CRC 细胞中的 IGFBP-2 水平。在缺乏 L1 增强的细胞增殖（在没有血清的情况下）、细胞迁移、肿瘤发生和诱导肝转移的情况下，CRC 细胞中 IGFBP-2 的过表达也可以增加这些特性，类似于 L1 的过表达。在转染 L1 的细胞中抑制内源性 IGFBP-2 抑制了 L1 赋予的这些特性。我们在正常黏膜的人结肠隐窝底部检测到 IGFBP-2 的独特组织，并在整个人 CRC 组织样本中检测到 IGFBP-2 的水平增加，与磷酸化的 p65 亚单位 NF-κB 共定位。最后，我们发现 IGFBP-2 和 L1 可以形成一个分子复合物，表明 L1 通过 L1-ezrin-NF-κB 途径介导的信号，诱导 IGFBP-2 的表达，在 CRC 进展中具有重要作用。
