Jianwei Ge

A glioma is the most common type of brain tumor that accounts for nearly 80 % of brain cancers. Vascular endothelial growth factor (VEGF) and its receptor, the kinase insert domain receptor (KDR), are involved in the angiogenesis of cancers. In this study, we investigate whether the polymorphisms of VEGF and KDR are associated with a glioma risk. Blood samples were collected from 477 glioma patients and 477 healthy controls. Five tag-single nucleotide polymorphisms (SNPs) of KDR were obtained from the HapMap database, and eight tag-SNPs of VEGF were selected based on previous studies. After extraction of genomic DNAs by a Qiagen DNA blood kit, the SNPs of VEGF and KDR were genotyped with a Sequenom MassArray iPLEX platform and further analyzed with matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. The odds ratios and their 95 % confidence interval (95 % CI) were used to assess the association between VEGF, KDR polymorphisms, and glioma risks with the aid of SPSS 13.0 software. The haplotype analysis demonstrated that two SNPs of VEGF [rs3025039 (C>T), rs2010963 (G>C)] could elevate the susceptibility to a glioma in the homozygous model [odds ratio (OR) = 3.13 (95 % confidence interval (CI) 1.30–7.49, P = 0.007) and OR = 1.58 (95 % CI 1.07–2.34, P = 0.022), respectively], dominant model [OR = 1.38 (95 % CI 1.04–1.84, P = 0.025) and OR = 1.32 (95 % CI 1.01–1.72, P = 0.043), respectively], and allelic model [OR = 1.43 (95 % CI 1.11–1.84, P = 0.005) and OR = 1.24 (95 % CI 1.04–1.50, P = 0.019), respectively]. Furthermore, three SNPs of KDR [rs7667298 (A>G), rs2305948 (C>T), rs1870377 (T>A)] were also assumed to be associated with an increased risk of a glioma in the homozygous [OR = 1.93 (95 % CI 1.30–2.86, P = 0.001), OR = 2.56 (95 % CI 1.28–5.11, P = 0.006), and OR = 1.52 (95 % CI 1.00–2.31, P = 0.049), respectively], dominant [OR = 1.52 (95 % CI 1.16–1.98, P = 0.002), OR = 1.41 (95 % CI 1.05–1.87, P = 0.020), and OR = 1.48 (95 % CI 1.13–1.93, P = 0.004), respectively], and allele models [OR = 1.39 (95 % CI 1.15–1.67, P = 0.001), OR = 1.47 (95 % CI 1.14–1.89, P = 0.002), and OR = 1.27 (95 % CI 1.05–1.52, P = 0.013), respectively]. The genetic polymorphisms of VEGF [rs3025039 (C>T), rs2010963 (G>C)] and KDR [rs7667298 (A>G), rs2305948 (C>T), rs1870377 (T>A)] increased glioma susceptibility in a Chinese population, suggesting the possibility of VEGF and KDR as genetic markers for glioma. Additional functional and association studies with different ethnic groups included are needed to further confirm our results.

Aberrant PDGF‐PDGFR signaling and its effects on downstream effectors have been implicated in glioma development. A crucial AKT regulator, ACK1 (TNK2) has been shown to be a downstream mediator of PDGF signaling; however, the exact underlying mechanisms in gliomas remain elusive. Here, we report that in glioma cells, PDGFR‐β activation enhanced the interaction between ACK1 and AKT, resulting in AKT activation. PDGF treatment consistently promoted the formation of complexes containing PDGFR‐β and ACK1. Mutational analysis suggested that Y635 of ACK1 is a PDGFR‐β phosphorylation site and that the ACK1 Y635F mutant abrogated the sequential activation of AKT. Moreover, PDK1 interacted with ACK1 during PDGF stimulation, which is required for the binding of ACK1 to PDGFR‐β. Further mutational analysis showed that T325 of ACK1 was crucial for the ACK1 and PDK1 interaction. ACK1 Y635F or T325A mutants abolished PDGFR‐β‐induced AKT activation, the subsequent nuclear translocation of β‐catenin and the expression of cyclin D1. Glioma cell cycle progression, proliferation and tumorigenesis were accordingly blocked by ACK1 Y635F or T325A. In glioblastoma multiforme samples from 51 patients, increased ACK1 tyrosine phosphorylation correlated with upregulated PDGFR‐β activity and AKT activation. Taken together, our data demonstrate that ACK1 plays a pivotal role in PDGF‐PDGFR‐induced AKT signaling in glioma tumorigenesis. This knowledge contributes to our understanding of glioma progression and may facilitate the identification of novel therapeutic targets for future glioma treatment.

Glioma is one of the most common solid tumors, and the molecular mechanism for this disease is poorly understood. EphB4 tyrosine kinase receptor has been involved in various physiologic and pathologic processes, and the role of EphB4 in tumorigenesis has recently attracted much interest. However, its function in glioma remains largely unknown. In this study, we explored the function of EphB4 in glioma. We found that the expression of EphB4 was significantly upregulated in clinical glioma samples. Overexpression of EphB4 in glioma cell lines accelerated cell growth and tumorigenesis. In contrast, downregulation of EphB4 inhibited cell growth. Furthermore, we showed that EphB4 promoted cell growth by promoting EGFR signaling. Taken together, our findings suggest that EphB4 plays an important role in the progression of glioma by stimulating cell growth and EphB4 might be a potential therapeutic target for glioma.

The Notch signaling pathway has been implicated in both developmental processes and tumorigenesis. Aberrant Notch signaling has been repeatedly demonstrated to facilitate the proliferation and survival of glioma cells by regulating downstream effectors or other signaling pathways. In glioblastoma multiforme specimens from 59 patients, Notch1 was highly expressed in tumor tissues compared with normal brain tissues, and this expression was correlated with elevated AKT phosphorylation and Snail expression. Increased nuclear localization of β‐catenin and p50 as well as enhanced IKKα/AKT interaction were also observed in glioma tissues. In U87MG cells, the activation of Notch1 by DLL4 stimulation or by the overexpression of Notch intracellular domain (NICD) resulted in AKT activation and thereby promoted β‐catenin activity and NF‐κB signaling. Inhibition of EGFR partially blocked the β‐catenin and NF‐κB signaling stimulated by Notch1 activation. Furthermore, NICD overexpression in U87MG cells led to the upregulated expression of several metastasis‐associated molecules, which could be abrogated by the knockdown of either β‐catenin or p50. In U87MG and U251 cells, DLL4‐induced cellular migration and invasion could be inhibited by either β‐catenin or a p50 inhibitor. Collectively, these results indicate that Notch activation could stimulate β‐catenin and NF‐κB signaling through AKT activation in glioma cells. Thus, Notch activation‐stimulated β‐catenin and NF‐κB signaling synergistically promote the migratory and invasive properties of glioma cells. (Cancer Sci 2012; 103: 181–190)