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.

Implications of MGMT methylation status in pituitary adenoma

BACKGROUND

Very little literature exists on frequency of MGMT methylation status in pituitary adenoma. We assessed the frequency of MGMT methylation and protein expression in pituitary adenoma and correlated with patients' age group and prognosis.

METHODS

Tumor tissues from 30 patients with pituitary adenoma were evaluated for MGMT promoter methylation status by methylation specific PCR method. All tumors were also immunostained with MIB-1, anti-p53 and anti-MGMT antibodies.

RESULTS

MGMT methylation status was noted in 40% of cases (7/20 non-functioning adenomas and 5/10 functioning adenomas). MGMT protein expression on IHC was noted in 72.2% of unmethylated tumors, while only 41.6% of methylated tumors demonstrated protein expression. The mean labeling index of MGMT protein was higher in unmethylated tumors as compared to the methylated group, though the difference was not statistically significant (18.6% vs 8.8%; p=0.131). Tumor regrowth occurred in four unmethylated tumors as compared to none in methylated group. Even though there was no correlation between patient age and MGMT methylation status (p=0.823), we noted that the frequency of methylation in middle age patients (between 30 and 59 yrs) was 64.7%, which was higher compared to other age groups.

CONCLUSION

This is the first study from India showing MGMT promoter methylation status with protein expression in pituitary adenoma. We noted that tumor regrowth was higher in unmethylated tumors.