Abstract. Programmed cell death protein 4 (PDCD4) has recently been demonstrated to be implicated in translation and transcription, and the regulation of cell growth. However, the mechanisms underlying PDCD4 function in glioma cells remain to be elucidated. The current study investigated the function and regulation of PDCD4 and the results demonstrated that the expression of PDCD4 was significantly reduced in glioma cells compared with normal cells. When PDCD4 was overexpressed in glioma cells, the proliferation rate and invasive capability of the cells greatly decreased, suggesting that PDCD4 functions as a tumor suppressor in this cell type. In addition, the histone modification status of the PDCD4 gene was analyzed, and chromatin immunoprecipitation assay identified a high density of histone 3 lysine 27 trimethylation on the promoter of PDCD4, which was associated with the long non-coding RNA, homeobox transcript antisense RNA (HOTAIR). The expression of HOTAIR was significantly increased in glioma cells compared with normal cells, and it exerted its function in a polycomb repressive complex 2-dependent manner. These results may provide novel approaches to therapeutically target PDCD4 and HOTAIR in patients with gliomas.
IntroductionHuman gliomas are the most prevalent malignant neoplasms of the central nervous system, with an annual incidence of ~5/100,000 worldwide (1). Despite the use of aggressive surgery in combination with chemotherapy, biological therapy and radiotherapy, gliomas continue to be therapeutically challenging (2). For patients with glioblastoma, the relative 5-year survival rate is <5% (3). Novel therapies for the treatment of glioma are warranted; recent advances in the understanding of the molecular and biological nature of this disease may facilitate the development of successful therapeutics (4).PDCD4 protein was initially determined to be overexpressed during apoptosis, which subsequently suppresses tumorigenesis (5,6). Loss of PDCD4 expression is closely associated with the progression of a number of tumors, including glioblastomas (7), and kidney, ovarian and lung cancer (8-10). Low PDCD4 expression levels correlate with poor outcomes in patients with glioblastoma multiforme (11). The frequent loss of PDCD4 in glioblastoma multiforme is partly due to epigenetic silencing secondary to 5' cytosine-phosphate-guanine island methylation (12), in addition to overexpression of microRNA (miRNA)-21, which targets PDCD4 mRNA for degradation (13). Although several studies have examined PDCD4 in glioma, the detailed molecular mechanisms underlying the role of PDCD4 in glioma remain poorly understood.Long non-coding RNAs (lncRNAs) are non-protein coding transcripts longer than 200 nucleotides, which are involved in various important events, including transcriptional, epigenetic and post-transcriptional regulation (14,15). A previous study profiled the lncRNA homeobox transcript antisense RNA (HOTAIR), and the results demonstrated that HOTAIR was closely correlated with poor prognosis, molecular ...