Ganesh Raksha A, Sonpatki Pranali, Naik Divya, John Arivusudar Everad, Sathe Gajanan, Lakshmikantha Akhila, Chandrachari Komal Prasad, Bauer Lea, Knäuper Vera, Aeschlimann Daniel, Venkatraaman Krishnan, Shah Nameeta, Sirdeshmukh Ravi
Mazumdar Shaw Center for Translational Research, Narayana Health, Bangalore, India.
Center for Bio-Separation Technology, Vellore Institute of Technology, Vellore, India.
Front Oncol. 2022 May 3;12:841890. doi: 10.3389/fonc.2022.841890. eCollection 2022.
G protein-coupled receptor 56 (GPR56/ADGRG1) is an adhesion GPCR with an essential role in brain development and cancer. Elevated expression of GPR56 was observed in the clinical specimens of Glioblastoma (GBM), a highly invasive primary brain tumor. However, we found the expression to be variable across the specimens, presumably due to the intratumor heterogeneity of GBM. Therefore, we re-examined GPR56 expression in public domain spatial gene expression data and single-cell expression data for GBM, which revealed that GPR56 expression was high in cellular tumors, infiltrating tumor cells, and proliferating cells, low in microvascular proliferation and peri-necrotic areas of the tumor, especially in hypoxic mesenchymal-like cells. To gain a better understanding of the consequences of GPR56 downregulation in tumor cells and other molecular changes associated with it, we generated a sh-RNA-mediated GPR56 knockdown in the GBM cell line U373 and performed transcriptomics, proteomics, and phospho-proteomics analysis. Our analysis revealed enrichment of gene signatures, pathways, and phosphorylation of proteins potentially associated with mesenchymal (MES) transition in the tumor and concurrent increase in cell invasion and migration behavior of the GPR56 knockdown GBM cells. Interestingly, our analysis also showed elevated expression of Transglutaminase 2 (TG2) - a known interactor of GPR56, in the knockdown cells. The inverse expression of GPR56 and TG2 was also observed in intratumoral, spatial gene expression data for GBM and in GBM cell lines cultured under hypoxic conditions. Integrating all these observations, we propose a putative functional link between the inverse expression of the two proteins, the hypoxic niche and the mesenchymal status in the tumor. Hypoxia-induced downregulation of GPR56 and activation of TG2 may result in a network of molecular events that contribute to the mesenchymal transition of GBM cells, and we propose a putative model to explain this functional and regulatory relationship of the two proteins.
G蛋白偶联受体56（GPR56/ADGRG1）是一种粘附性GPCR，在大脑发育和癌症中起着至关重要的作用。在胶质母细胞瘤（GBM）的临床标本中观察到GPR56表达升高，GBM是一种具有高度侵袭性的原发性脑肿瘤。然而，我们发现不同标本中的表达存在差异，这可能是由于GBM的肿瘤内异质性所致。因此，我们重新检查了GBM的公共领域空间基因表达数据和单细胞表达数据中的GPR56表达，结果显示GPR56在细胞性肿瘤、浸润性肿瘤细胞和增殖细胞中表达较高，在肿瘤的微血管增殖和坏死周边区域表达较低，尤其是在低氧间充质样细胞中。为了更好地了解肿瘤细胞中GPR56下调的后果以及与之相关的其他分子变化，我们在GBM细胞系U373中通过sh-RNA介导敲低GPR56，并进行了转录组学、蛋白质组学和磷酸化蛋白质组学分析。我们的分析揭示了肿瘤中与间充质（MES）转变潜在相关的基因特征、信号通路和蛋白质磷酸化的富集，以及GPR56敲低的GBM细胞的细胞侵袭和迁移行为同时增加。有趣的是，我们的分析还显示，在敲低细胞中，转谷氨酰胺酶2（TG2）——一种已知的GPR56相互作用蛋白——的表达升高。在GBM的肿瘤内空间基因表达数据以及在低氧条件下培养的GBM细胞系中，也观察到了GPR56和TG2的反向表达。综合所有这些观察结果，我们提出这两种蛋白质的反向表达、低氧微环境与肿瘤中间充质状态之间存在一种假定的功能联系。低氧诱导的GPR56下调和TG2激活可能导致一系列分子事件，促成GBM细胞的间充质转变，我们提出了一个假定模型来解释这两种蛋白质的这种功能和调节关系。
