CBX3 promotes glioma U87 cell proliferation and predicts an unfavorable prognosis.

BACKGROUND: Chromobox protein homolog 3 (CBX3) is one of the heterochromatin protein 1 (HP1) family members. Among multiple cancers, it is usually overexpressed. However, the mechanism and function of CBX3 in glioma remain incompletely illustrated.
METHODS: The expression level of CBX3 as well as its correlation with glioma are detected through TCGA and Oncomine database. The expressions of CBX3 mRNA and protein in glioma tissues and normal brain tissues have been identified by qRT-PCR and Western blot. The prognostic role of CBX3 has been assessed in a retrospective cohort study. Additionally, the correlation between CBX3 expression and the clinicopathological characteristics of glioma patients were also discussed. To better understand the role of CBX3 in glioma, a lentiviral vector expressing CBX3-shRNA and cyclin dependent kinase inhibitor 1A (CDKN1A) siRNA were established and transfected into the glioma U87 cells. Besides, the CBX3 and CDKN1A expression levels in glioma U87 cells after transfected with CBX3-shRNA were gauged by qRT-PCR and Western blot. CCK-8, colony formation and EdU assays have been applied to evaluate the influence of CBX3 on U87 cells proliferation, and flow cytometry has been applied to manage the changes in cell cycle and cell apoptosis after transfection with CBX3-shRNA. Xenograft tumors have been examined in vivo for the carcinogenic effects and prognostic value of CBX3 in glioma tissues.
RESULTS: In the present study, CBX3 was demonstrated to be highly expressed in human glioma tissues, and high CBX3 expression predicted the dismal recurrence-free survival (RFS) and poor overall survival (OS) for glioma patients. High CBX3 expression was dependent on the tumor size, Karnofsky performance scale (KPS) score, WHO grade, recurrence and survival status. Moreover, CBX3 expression knockdown could remarkably suppress the proliferation and colony formation ability of U87 cells, which was achieved through blocking cell arrest at G0/G1 phase and inducing apoptosis. Additionally, our findings also suggested that, compared with shRNA-Ctrl transfection, the mRNA and protein expression levels of CDKN1A have been dramatically up-regulated in vitro after transfection with shRNA-CBX3. Consistent with the results of in vitro assays, the outcomes of xenograft assay and immunohistochemistry (IHC) also indicated that, the tumor growth and Ki-67 expression level were restrained in response to CBX3 inhibition, while the CDKN1A expression level in vivo was up-regulated. Down-regulation of CDKN1A expression partially restored the ability of cell proliferation in the U87 cells, which was inhibited by shRNA-CBX3
CONCLUSIONS: In conclusion, results of the current research suggest that a high CBX3 expression level predicts the poor prognosis for glioma patients. CBX3 can stimulate the growth of glioma U87 cells through targeting CDKN1A and CBX3 may become a novel target in the clinical treatment for glioma.