Preferential Expression of B7‐H6 in Glioma Stem‐Like Cells Enhances Tumor Cell Proliferation via the c‐Myc/RNMT Axis
Hanqing Chen, Yundi Guo, Jing Sun, Jun Dong, Qinghua Bao, Xueguang Zhang, Fengqing Fu
Abstract
B7 homologue 6 (B7‐H6), a newly identified member of the B7 costimulatory molecule family, is not only a crucial regulator of NK cell‐mediated immune responses through binding to NKp30 but also has clinical implications due to its abnormal expression in human cancers. Here, we show that B7‐H6 expression is abnormally upregulated in glioma tissue and that B7‐H6 is coexpressed with stem cell marker Sox2. Intriguingly, B7‐H6 was rarely detected on the surface of glioma cell lines but was abundantly expressed in glioma stem‐like cells (GSLCs) that were derived from the glioma cell lines in vitro . Surprisingly, B7‐H6 was the only one that was preferentially expressed in the GSLCs among the B7 family members. Functionally, knockdown of B7‐H6 in GSLCs by siRNAs led to the inhibition of cell proliferation, with decrease in the expression of the oncogene Myc as well as inactivation of PI3K/Akt and ERK/MAPK signaling pathways. Moreover, we determined that three genes CBL (Casitas B‐Lineage Lymphoma Proto‐Oncogene), CCNT1 (Cyclin T1), and RNMT (RNA guanine‐7 methyltransferase) were coexpressed with B7‐H6 and c‐myc in glioma tissue samples from the TCGA database and found, however that only RNMT expression was inhibited by the knockdown of B7‐H6 expression in the GSLCs, suggesting the involvement of RNMT in the B7‐H6/c‐myc axis. Extending this to 293T cells, we observed that knocking out of B7‐H6 with CRISPR‐Cas9 system also suppressed cell proliferation. Thus, our findings suggest B7‐H6 as a potential molecule for glioma stem cell targeted immunotherapy.