Supplementary Figure 1. TIP47 staining represents lipid droplets in cancer cell lines. Supplementary Figure 2. LD number is correlated with Ki67 positive percentage in GBM patient tumor tissues. Supplementary Figure 3. SOAT1 is majorly expressed in GBM patient tumor tissues and cell lines. Supplementary Figure 4. Genetic or pharmacologic inhibition of SOAT1 suppresses lipid droplet formation in GBM cells. Supplementary Figure 5. Genetic or pharmacologic inhibition of SOAT1 does not significantly advance GBM cell cholesterol levels. Supplementary Figure 6. Genetic or pharmacologic inhibition of SOAT1 suppresses SREBP-1 activation and reduces the expression of its downstream targets. Supplementary Figure 7. Inhibition of SOAT1 has no inhibitory effect on LDL uptake.
ARTICLE ABSTRACT
Purpose: Elevated lipogenesis regulated by sterol regulatory element-binding protein-1 (SREBP-1), a transcription factor playing a central role in lipid metabolism, is a novel characteristic of glioblastoma (GBM). The aim of this study was to identify effective approaches to suppress GBM growth by inhibition of SREBP-1. As SREBP activation is negatively regulated by endoplasmic reticulum (ER) cholesterol, we sought to determine whether suppression of sterol O-acyltransferase (SOAT), a key enzyme converting ER cholesterol to cholesterol esters (CE) to store in lipid droplets (LDs), effectively suppressed SREBP-1 and blocked GBM growth.Experimental Design: The presence of LDs in glioma patient tumor tissues was analyzed using immunofluorescence, immunohistochemistry, and electronic microscopy. Western blotting and real-time PCR were performed to analyze protein levels and gene expression of GBM cells, respectively. Intracranial GBM xenografts were used to determine the effects of genetically silencing SOAT1 and SREBP-1 on tumor growth.Results: Our study unraveled that cholesterol esterification and LD formation are signature of GBM, and human patients with glioma possess elevated LDs that correlate with GBM progression and poor survival. We revealed that SOAT1 is highly expressed in GBM and functions as a key player in controlling the cholesterol esterification and storage in GBM. Targeting SOAT1 suppresses GBM growth and prolongs survival in xenograft models via inhibition of SREBP-1–regulated lipid synthesis.Conclusions: Cholesterol esterification and storage in LDs are novel characteristics of GBM, and inhibiting SOAT1 to block cholesterol esterification is a promising therapeutic strategy to treat GBM by suppressing SREBP-1. Clin Cancer Res; 22(21); 5337–48. ©2016 AACR.
