Department of Biochemistry, National University of Singapore, Singapore.
J Neurochem. 2010 Nov;115(3):759-70. doi: 10.1111/j.1471-4159.2010.06975.x. Epub 2010 Sep 28.
Malignant gliomas are highly invasive neuroepithelial tumors where the tendency to invade and migrate away from the primary tumor mass is thought to be a leading cause of tumor recurrence and treatment failures. Autocrine signals produced by secreted factors that signal through receptors on the tumor are known to contribute to the invasiveness. Glial cell line-derived neurotrophic factor and GDNF family receptor alpha 1 (GFRα1) are over-expressed in human gliomas. We have previously reported that human gliomas express high levels of GFRα1b, an alternatively spliced isoform of GFRα1. However, the functional significance of GFRα1b in glioma behaviors is currently unknown. In this study, we have designed isoform-specific small-interfering RNA to knockdown the highly homologous GFRα1a or GFRα1b isoform efficiently in malignant C6 glioma cells. Unexpectedly, the knockdown of GFRα1b but not GFRα1a induced cell elongation and inhibited C6 cell migration and invasion in vitro. In addition, GFRα1b was found to regulate the expression of RhoA small GTPase, which was required for migration of C6 cells. The decreases in RhoA expression and cell migration after GFRα1b knockdown were attenuated by small-interfering RNA -resistant GFRα1b but not GFRα1a, further demonstrating the specific role of GFRα1b in glioma migration. Interestingly, the knockdown of NCAM but not receptor tyrosine kinase Ret resulted in the reduction of RhoA expression and C6 cell migration. Taken together, these unanticipated results indicate that GFRα1b is involved in glioma migration through glial cell line-derived neurotrophic factor -GFRα1b-NCAM signaling complex and modulation of RhoA expression.
恶性神经胶质瘤是高度侵袭性的神经上皮肿瘤，其侵袭和迁移远离原发性肿瘤的倾向被认为是肿瘤复发和治疗失败的主要原因。通过肿瘤上的受体发出信号的分泌因子产生的自分泌信号被认为有助于侵袭性。胶质细胞衍生的神经营养因子和 GDNF 家族受体 alpha 1（GFRα1）在人类神经胶质瘤中过度表达。我们之前报道过，人类神经胶质瘤表达高水平的 GFRα1b，这是 GFRα1 的一种剪接异构体。然而，GFRα1b 在神经胶质瘤行为中的功能意义目前尚不清楚。在这项研究中，我们设计了异构体特异性的小干扰 RNA，有效地敲低恶性 C6 神经胶质瘤细胞中的高度同源 GFRα1a 或 GFRα1b 异构体。出乎意料的是，敲低 GFRα1b 而不是 GFRα1a 诱导细胞伸长，并抑制 C6 细胞在体外的迁移和侵袭。此外，发现 GFRα1b 调节 RhoA 小 GTPase 的表达，这是 C6 细胞迁移所必需的。GFRα1b 敲低后 RhoA 表达和细胞迁移减少可被 GFRα1b 而不是 GFRα1a 的抗性小干扰 RNA 减弱，进一步证明了 GFRα1b 在神经胶质瘤迁移中的特异性作用。有趣的是，敲低 NCAM 而不是受体酪氨酸激酶 Ret 导致 RhoA 表达和 C6 细胞迁移减少。总之，这些意外的结果表明，GFRα1b 通过胶质细胞衍生的神经营养因子-GFRα1b-NCAM 信号复合物和 RhoA 表达的调节参与神经胶质瘤的迁移。
