Study on the crucial role of BST-2 as a cancer stem cell marker in glioblastoma

Abstract

Introduction: Glioblastoma multiforme (GBM) are highly lethal primary brain tumors and consist of heterogeneous cell populations. Because this distinct character, GBM cells adapt to various factors in tumor microenvironment. Among diverse populations of GBM, glioblastoma stem cells (GSCs) have been reported that are highly tumorigenic, chemo- and radio-resistant, and tumor recurring properties. Although many studies made efforts to define specific markers such as CD133, recent studies raised a possibility that CD133 may be insufficient marker to represent all of GSCs. Thus, identification of novel markers as GSCs is important for the prevention and treatment with GBM t. Here, I suggest that BST-2 is one of the crucial markers and regulators of self-renewal abilities in GSCs. Overexpressed BST-2 is demonstrated in many types of cancers that enhanced tumor aggressiveness, including invasion, metastasis and drug-resistance. Moreover, hypomethylation of BST-2 in its promoter leads to enhance the expression of BST-2 in GBM. However, the relevance between high levels of BST-2 and stemness in GBM is remained unknown.

Methods: To evaluate the roles of BST-2 in GSCs, I have established cancer stem cell (CSC)-like cells possessing the capacity to maintain self-renewal. To confirm the effect of BST-2 on tumorigenicity, I used xenograft and serial transplantation mouse models. Gain or loss of function was examined by transfection with BST-2 expression construct and BST-2 mRNA-specific si/shRNA. To identify potential microenvironments enhancing BST-2 expression, GBM cells were incubated in a hypoxic incubator with a 94:5:1 % mixture of N2:CO2:O2.

Results: Upregulation of the BST-2 is correlated with poor survival of GBM patients. In vitro experiments showed that the BST-2 expression was enhanced in cultured spheroid GBM cells, while this expression was abolished in the presence of differentiation factors, suggesting an essential role of BST-2 on stem cell-like property in GBM. Knockdown of BST-2 expression with shRNA or siRNA in sphere-formed GBM leads to loss of their stemness properties. In vivo models, subcutaneously injection with spheroid cells into the dorsal flank of Balb/c nude mice exhibited more tumorigenic and self-renewal capacities. The sphere-formed cells were generated from the primary and secondary tumors, at that time, BST-2 positive cell populations were maintained during the development of secondary tumors. From the mechanistic studies, BST-2 inhibited GSK3 activity, resulting in activation of the -catenin signaling pathway. In addition, BST-2 contains the binding motifs of HIF-1 and STAT3 in its promoter regions that was synergistically promoted the transcription activity and expression of BST-2 in a hypoxic microenvironment.

Conclusions: Taken together, these studies were demonstrated the crucial roles of BST-2 as a CSC marker in GBM and these results are novel findings that are may suggest a potential therapeutic target in patients with GBMs.