Department of Neuroscience & Physiology, SUNY Upstate Medical University, Syracuse, New York, USA.
Department of Neurosurgery, SUNY Upstate Medical University, Syracuse, New York, USA.
Neuro Oncol. 2022 Aug 1;24(8):1230-1242. doi: 10.1093/neuonc/noac001.
Tumor invasion, a hallmark of malignant gliomas, involves reorganization of cell polarity and changes in the expression and distribution of scaffolding proteins associated with polarity complexes. The scaffolding proteins of the DLG family are usually downregulated in invasive tumors and regarded as tumor suppressors. Despite their important role in regulating neurodevelopmental signaling, the expression and functions of DLG proteins have remained almost entirely unexplored in malignant gliomas.
Western blot, immunohistochemistry, and analysis of gene expression were used to quantify DLG members in glioma specimens and cancer datasets. Over-expression and knockdown of DLG5, the highest-expressed DLG member in glioblastoma, were used to investigate its effects on tumor stem cells and tumor growth. qRT-PCR, Western blotting, and co-precipitation assays were used to investigate DLG5 signaling mechanisms.
DLG5 was upregulated in malignant gliomas compared to other solid tumors, being the predominant DLG member in all glioblastoma molecular subtypes. DLG5 promoted glioblastoma stem cell invasion, viability, and self-renewal. Knockdown of this protein in vivo disrupted tumor formation and extended survival. At the molecular level, DLG5 regulated Sonic Hedgehog (Shh) signaling, making DLG5-deficient cells insensitive to Shh ligand. Loss of DLG5 increased the proteasomal degradation of Gli1, underlying the loss of Shh signaling and tumor stem cell sensitization.
The high expression and pro-tumoral functions of DLG5 in glioblastoma, including its dominant regulation of Shh signaling in tumor stem cells, reveal a novel role for this protein that is strikingly different from its proposed tumor-suppressor role in other solid tumors.
肿瘤侵袭是恶性神经胶质瘤的一个标志，涉及细胞极性的重新组织以及与极性复合物相关的支架蛋白表达和分布的变化。DLG 家族的支架蛋白在侵袭性肿瘤中通常下调，被认为是肿瘤抑制因子。尽管它们在调节神经发育信号方面起着重要作用，但 DLG 蛋白在恶性神经胶质瘤中的表达和功能几乎完全没有被探索过。
使用 Western blot、免疫组织化学和基因表达分析来定量分析神经胶质瘤标本和癌症数据集中的 DLG 成员。过表达和敲低最高表达的 DLG 成员 DLG5，以研究其对肿瘤干细胞和肿瘤生长的影响。使用 qRT-PCR、Western blot 和共沉淀实验来研究 DLG5 的信号转导机制。
与其他实体瘤相比，DLG5 在恶性神经胶质瘤中上调，是所有神经胶质瘤分子亚型中主要的 DLG 成员。DLG5 促进神经胶质瘤干细胞的侵袭、活力和自我更新。体内敲低这种蛋白质会破坏肿瘤的形成并延长存活时间。在分子水平上，DLG5 调节 Sonic Hedgehog (Shh) 信号，使 DLG5 缺陷细胞对 Shh 配体不敏感。DLG5 的缺失增加了 Gli1 的蛋白酶体降解，从而导致 Shh 信号的丢失和肿瘤干细胞的敏化。
DLG5 在神经胶质瘤中的高表达和促肿瘤功能，包括其对肿瘤干细胞中 Shh 信号的主导调节，揭示了这种蛋白质的一个新作用，与它在其他实体瘤中被认为是肿瘤抑制因子的作用明显不同。
