Insulin-like growth factor binding protein-2 regulates ß-catenin signaling pathway in glioma cells and contributes to poor patient prognosis.

BACKGROUND: Upregulation of insulin-like growth factor binding protein 2 (IGFBP-2) is often associated with aggressiveness of glioblastoma (GBM) and contributes to poor prognosis for GBM patients. In view of the regulation of ß-catenin by IGFBP-2 in breast cancer and the crucial role of ß-catenin pathway in glioma invasion, proliferation and maintenance of glioma stem cells, the mechanism of regulation of ß-catenin by IGFBP-2, and its role in GBM prognosis was studied. METHODS: Regulation of the ß-catenin pathway was studied by immunocytochemistry, Western blot analysis, luciferase assays, and real-time RT-PCR. The role of IGFBP-2 was studied by subcutaneous tumor xenografts in immunocompromised mice using glioma cells engineered to express IGFBP-2 and its domains. GBM patient tumor tissues (n = 112) were analyzed for expression of IGFBP-2 and ß-catenin by immunohistochemistry. Survival analysis was performed employing Cox regression and Kaplan-Meier survival analyses. RESULTS: IGFBP-2 knockdown in U251, T98G, and U373 or overexpression in LN229 and U87 cells revealed a role for IGFBP-2 in stabilization of ß-catenin and regulation of its nuclear functions involving integrin-mediated inactivation of GSK3ß. Similar results were obtained upon overexpression of the C-terminal domain of IGFBP-2 but not the N-terminal domain. Subcutaneous xenograft tumors overexpressing either full-length or the C-terminal domain of IGFBP-2 showed larger volume as compared with controls. Coexpression of high levels of IGFBP-2 and ß-catenin was associated with worse prognosis (P = .001) in GBM patients. CONCLUSION: IGFBP-2 potentiates GBM tumor growth by the activation of the ß-catenin pathway through its C-terminal domain, and their coexpression possibly contributes to worse patient prognosis.

Manganese superoxide dismutase (MnSOD) is a malignant astrocytoma specific biomarker and associated with adverse prognosis in p53 expressing glioblastoma.

BACKGROUND: Manganese super oxide dismutase (MnSOD) has been previously identified as one of the top regulated genes associated with poor survival in glioblastoma (GBM) patients. In the current study we have evaluated the protein expression of MnSOD across various grades of astrocytoma, studied its influence on survival of GBM patients and following recurrence. METHODS: The protein expression of MnSOD was analyzed on tumor tissue sections by immunohistochemistry on 30 diffuse astrocytomas (DA), 50 anaplastic astrocytomas (AA), 30 paired (primary and recurrent) GBM samples and 30 non-tumor brain tissues. The protein expression among the different grades of diffusely infiltrating astrocytoma (DIA) was evaluated by Kruskal-Wallis one-way ANOVA followed by post hoc test. Wilcoxon matched pair test was employed to assess MnSOD protein expression across 30 paired GBM samples (primary and recurrent). The prognostic impact of MnSOD protein expression individually and following stratification with p53 expression was evaluated in a cohort of 123 GBM patients. Both over-all survival (OS) and progression free survival (PFS) analysis were performed by employing Cox regression analysis and Kaplan-Meier survival analysis on GBM patients. RESULTS: A significantly increased protein expression of MnSOD was observed among malignant astrocytomas (GBM and AA) in comparison with either DA or non-tumor brain tissues (p<0.05). Among the GBM cases it was noted that the IDH1 immunopositive tumors (R132H mutant protein; n=17) had a low MnSOD expression as opposed to IDH1 immunonegative tumors (n=106), which had high expression of MnSOD (p=0.0307). Further, a statistically significant increase (p=0.010) in extent of MnSOD protein expression was also noted in GBM tumors following recurrence. Protein expression of MnSOD was associated with both poor OS (HR: 1.021; p=0.011) and early PFS (HR: 1.022; p=0.006) on univariate analysis. Multivariate Cox regression analysis as well as Kaplan-Meier survival analysis demonstrated similar poor prognostic association. Stratification of GBM cases based on p53 expression status revealed a strong association of MnSOD with OS (HR: 1.042; p=0.002) and PFS (HR: 1.044; p=0.001) in p53 positive tumor tissue samples. Similar findings were noted on multivariate Cox regression analysis and K-M survival analysis, while no such association was noted in tumor tissues staining negative for p53 expression. CONCLUSIONS: Our study shows an increased expression of MnSOD in anaplastic astrocytoma and GBM compared to low grade astrocytoma and control brain. An increase in MnSOD expression following GBM tumor recurrence strengthens its putative role in tumor aggressiveness. Further, MnSOD emerges as a poor prognostic biomarker in p53 expressing GBMs, rendering this molecule as a potential therapeutic target in such patients.

Glioblastoma-derived Macrophage Colony-stimulating Factor (MCSF) Induces Microglial Release of Insulin-like Growth Factor-binding Protein 1 (IGFBP1) to Promote Angiogenesis.

Glioblastoma (grade IV glioma/GBM) is the most common primary adult malignant brain tumor with poor prognosis. To characterize molecular determinants of tumor-stroma interaction in GBM, we profiled 48 serum cytokines and identified macrophage colony-stimulating factor (MCSF) as one of the elevated cytokines in sera from GBM patients. Both MCSF transcript and protein were up-regulated in GBM tissue samples through a spleen tyrosine kinase (SYK)-dependent activation of the PI3K-NFκB pathway. Ectopic overexpression and silencing experiments revealed that glioma-secreted MCSF has no role in autocrine functions and M2 polarization of macrophages. In contrast, silencing expression of MCSF in glioma cells prevented tube formation of human umbilical vein endothelial cells elicited by the supernatant from monocytes/microglial cells treated with conditioned medium from glioma cells. Quantitative proteomics based on stable isotope labeling by amino acids in cell culture showed that glioma-derived MCSF induces changes in microglial secretome and identified insulin-like growth factor-binding protein 1 (IGFBP1) as one of the MCSF-regulated proteins secreted by microglia. Silencing IGFBP1 expression in microglial cells or its neutralization by an antibody reduced the ability of supernatants derived from microglial cells treated with glioma cell-conditioned medium to induce angiogenesis. In conclusion, this study shows up-regulation of MCSF in GBM via a SYK-PI3K-NFκB-dependent mechanism and identifies IGFBP1 released by microglial cells as a novel mediator of MCSF-induced angiogenesis, of potential interest for developing targeted therapy to prevent GBM progression.

Definition of a serum marker panel for glioblastoma discrimination and identification of Interleukin 1ß in the microglial secretome as a novel mediator of endothelial cell survival induced by C-reactive protein.

Glioblastoma (GBM) is the most common malignant adult primary brain tumor. We profiled 724 cancer-associated proteins in sera of healthy individuals (n=27) and GBM (n=28) using antibody microarray. While 69 proteins exhibited differential abundance in GBM sera, a three-marker panel (LYAM1, BHE40 and CRP) could discriminate GBM sera from that of healthy donors with an accuracy of 89.7% and p<0.0001. The high abundance of C-reactive protein (CRP) in GBM sera was confirmed in 264 independent samples. High levels of CRP protein was seen in GBM but without a change in transcript levels suggesting a non-tumoral origin. Glioma-secreted Interleukin 6 (IL6) was found to induce hepatocytes to secrete CRP, involving JAK-STAT pathway. The culture supernatant from CRP-treated microglial cells induced endothelial cell survival under nutrient-deprivation condition involving CRP-FcγRIII signaling cascade. Transcript profiling of CRP-treated microglial cells identified Interleukin 1ß (IL1ß) present in the microglial secretome as the key mediator of CRP-induced endothelial cell survival. IL1ß neutralization by antibody-binding or siRNA-mediated silencing in microglial cells reduced the ability of the supernatant from CRP-treated microglial cells to induce endothelial cell survival. Thus our study identifies a serum based three-marker panel for GBM diagnosis and provides leads for developing targeted therapies. Biological significance A complex antibody microarray based serum marker profiling identified a three-marker panel - LYAM1, BHE40 and CRP as an accurate discriminator of glioblastoma sera from that of healthy individuals. CRP protein is seen in high levels without a concomitant increase of CRP transcripts in glioblastoma. Glioma-secreted IL6 induced hepatocytes to produce CRP in a JAK-STAT signaling dependent manner. CRP induced microglial cells to release IL1ß which in turn promoted endothelial cell survival. This study, besides defining a serum panel for glioblastoma discrimination, identified IL1ß as a potential candidate for developing targeted therapy.

Methylation silencing of ULK2, an autophagy gene, is essential for astrocyte transformation and tumor growth.

Glioblastoma (GBM) is the most aggressive type of brain tumor and shows very poor prognosis. Here, using genome-wide methylation analysis, we show that G-CIMP+ and G-CIMP-subtypes enrich distinct classes of biological processes. One of the hypermethylated genes in GBM, ULK2, an upstream autophagy inducer, was found to be down-regulated in GBM. Promoter hypermethylation of ULK2 was confirmed by bisulfite sequencing. GBM and glioma cell lines had low levels of ULK2 transcripts, which could be reversed upon methylation inhibitor treatment. ULK2 promoter methylation and transcript levels showed significant negative correlation. Ectopic overexpression of ULK2-induced autophagy, which further enhanced upon nutrient starvation or temozolomide chemotherapy. ULK2 also inhibited the growth of glioma cells, which required autophagy induction as kinase mutant of ULK2 failed to induce autophagy and inhibit growth. Furthermore, ULK2 induced autophagy and inhibited growth in Ras-transformed immortalized Baby Mouse Kidney (iBMK) ATG5(+/+) but not in autophagy-deficient ATG5(-/-) cells. Growth inhibition due to ULK2 induced high levels of autophagy under starvation or chemotherapy utilized apoptotic cell death but not at low levels of autophagy. Growth inhibition by ULK2 also appears to involve catalase degradation and reactive oxygen species generation. ULK2 overexpression inhibited anchorage independent growth, inhibited astrocyte transformation in vitro and tumor growth in vivo. Of all autophagy genes, we found ULK2 and its homologue ULK1 were only down-regulated in all grades of glioma. Thus these results altogether suggest that inhibition of autophagy by ULK1/2 down-regulation is essential for glioma development.

IDH1 mutations in diffusely infiltrating astrocytomas: grade specificity, association with protein expression, and clinical relevance.

IDH1 mutations are frequent genetic alterations in low-grade diffuse gliomas and secondary glioblastoma (GBM). To validate mutation frequency, IDH1 gene at codon 132 was sequenced in 74 diffusely infiltrating astrocytomas: diffuse astrocytoma (DA; World Health Organization [WHO] grade II), anaplastic astrocytoma (AA; WHO grade III), and GBM (WHO grade IV). All cases were immunostained with IDH1-R132H monoclonal antibody. Mutational status was correlated with mutant protein expression, patient age, duration of symptoms, and prognosis of patients with GBM. We detected 31 (41.9%) heterozygous IDH1 mutations resulting in arginine-to-histidine substitution (R132H;CGT-CAT). All 12 DAs (100%), 13 of 14 AAs (92.9%), and 6 of 48 GBMs (12.5%) (5/6 [83.3%] secondary, and 1/42 [2.4%] primary) harbored IDH1 mutations. The correlation between mutational status and protein expression was significant (P < . 001). IDH1 mutation status, though not associated with prognosis of patients with GBM, showed significant association with younger age and longer duration of symptoms in the whole cohort (P < .001). Our study validates IDH1 mutant protein expression across various grades of astrocytoma, and demonstrates a high incidence of IDH1 mutations in DA, AA, and secondary GBM.