Date Published: August 2, 2017
Publisher: Impact Journals LLC
Author(s): Bo Han, Xiangqi Meng, Hui Chen, Lingchao Chen, Xing Liu, Hongjun Wang, Daming Liu, Fei Gao, Lin Lin, Jianguang Ming, Bo Sun, Shi Yin, Ruijia Wang, Pengfei Wu, Jinquan Cai, Chuanlu Jiang.
Glioblastoma is the most malignant type of brain tumor, and its high invasiveness and multiplication severely shortens patients’ overall survival. The embryonic pyruvate kinase M2 (PKM2) isoform is highly expressed in human cancer. We used computational target gene prediction, in vitro cell culture, immunoblotting, quantitative real-time PCR, ATP measurements, luciferase reporter assays, wound-healing assays, Transwell assays, RNA immunoprecipitation PCR, co-immunoprecipitation, flow cytometry and tumor xenografts to study the regulation of the PKM2/β-catenin axis in glioma. PKM2 was predicted to be a potential target of miR-338. MiR-338 was downregulated in high-grade gliomas due to hypermethylation of CpG islands in its promoter, and ectopic expression of miR-338 inhibited cell proliferation, invasion and ATP generation. MiR-338 inhibited PKM2 expression by binding to the 3′ untranslated region of PKM2, which ultimately prevented binding of PKM2 to β-catenin and reduced T-cell factor/lymphoid enhancer factor reporter gene transcriptional activity. MiR-338 also inhibited PKM2 expression, attenuated glioma growth and prolonged survival in an animal model. These results confirm that miR-338, a tumor suppressor, suppresses the PKM2/β-catenin axis and is downregulated in glioblastoma. This provides a theoretical basis for glioma-targeting therapy.
Malignant primary brain tumors are major causes of cancer-related death in children and adults. Glioblastoma, the most common and lethal type of primary intracranial tumor, is highly infiltrative, progresses rapidly, and is relatively resistant to both radiotherapy and common chemotherapeutic agents.
Although there have already been several studies on miRNAs and their cancer-related functions, little has been known about the involvement of miRNAs in the PKM2-β-catenin axis. PKM2 is widely expressed in human cancers and has critical functions in several types of human neoplasia, including prostate cancer, promyelocytic leukemia and glioma [17-19]. PKM2 is also a key kinase in the Warburg effect, the main energy reaction in cancer cells; thus, disrupting PKM2 expres-sion could suppress tumorigenesis. Earlier studies indicated that PKM2 could be upregulated by mTOR and that disruption of PKM2 expression could suppress mTOR-induced tumorigenesis . However, in recent years, PKM2 has been found to exert a great influence on cancer cells, including on non-metabolic pathways, cell cycling, transcription factor distribution and chemotherapy resistance [21-23]. PKM2 can also regulate the Wnt signaling pathway by combining with β-catenin and adjusting its transcriptional activity, and can regulate gene transcription as a protein kinase that phosphorylates histone H3 [8, 12]. In this study, we found that PKM2 expression increased with glioma grade, and that glioblastoma patients with higher PKM2 expression had worse outcomes. Exogenous expression of PKM2 increased glioma cell proliferation, invasiveness and metabolism, while inhibition of PKM2 expression restrained these effects.