The Mechanism of Autophagy Induced by Histone Deacetylase Inhibitor (SAHA) in Glioblastoma Stem Cell

• Main Authors: Ming-Tsang Chiao, 矯明昌
• Other Authors: Jiunn-Liang Ko
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/64775778137449422385

博士 === 中山醫學大學 === 醫學研究所 === 101 === We report that glioblastoma stem-like cells (GSCs) can form vasculogenic mimicry in tumor xenografts and express pro-vascular molecules. We isolated GSCs from resected human glioblastoma tissues and demonstrated their stemness, differentiation, and in vivo tumor-initiating potential. Through a limiting dilution assay, CD133+ (CD133+-GSC) and CD133- (CD133--GSC) subpopulation of GSCs were obtained. Orthotopic xenotransplantation study revealed that these two subpopulations of GSCs shared similar efficacy in tumor formation but showed distinct intratumor vasculature. In comparison with xenografted tumors derived from CD133--GSC, a highly vascularized anaplastic tumor, mimicking vasculogenic mimicry, was found in CD133+-GSC-derived tumor xenografts. Subsets of CD133+-GSC but not CD133--GSC were capable of vascular smooth muscle-like cell differentiation, in vitro and in vivo. In tumor xenografts, endothelium-associated CD31 gene was detected in implanted CD133--GSC and exclusively dispersed within the tumor tissues. Although, the detailed action mechanisms required further investigation, this study demonstrated the vasculogenic capacity of brain GSCs and their cellular plasticity. The results of expression of pro-vascular molecules and differentiation of vascular-like cells suggest that GSCs may contribute to form vessel-like structures and provide a blood supply for glioblastoma cells. In addition, although Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, has been used in clinical trials for cancer therapies, its pharmacological effects occur through a poorly understood mechanism. Here, we report that SAHA specifically triggers autophagy and reduces cell viability via promotion of apoptosis in the late phase of glioblastoma stem cells (GSCs). Using a cell line cultured from a glioblastoma biopsy, we investigated the properties and effects of GSCs under SAHA treatment in vitro. In vivo xenograft assays revealed that SAHA effectively caused tumor growth slowdown and the induction of autophagy. SAHA was sufficient to increase formation of intracellular acidic vesicle organelles, recruitment of LC3-II to the autophagosomes, potentiation of BECN1 protein levels, and reduced SQSTM1 levels. We determined that SAHA triggered autophagy through the downregulation of AKT-mTOR signaling, a major suppressive cascade of autophagy. Interestingly, upon depletion or pharmacological inhibition of autophagy, SAHA facilitates apoptosis and results in cell death at the early phase, suggesting that SAHA-induced autophagy functions probably act as a prosurvival mechanism. Furthermore, our results also indicated that the inhibition of SAHA-induced autophagy using chloroquine has synergistic effects that further increase apoptosis. Moreover, we found that a reduced dose of SAHA functioned as a potent modulator of differentiation and senescence. Taken together, our results provide a new perspective on the treatment of GSCs, indicating that SAHA is a promising agent for targeting GSCs through the induction of autophagy.