Aberrant Control of Transcription and Transportation of Oncogenic mRNA in Carcinogenesis

Abstract

Multiple gene disorders have been shown to be involved in carcinogenesis. Mutation, translocation and amplification have been identified in so-called oncogenes, and inactivation of antioncogenes by mutation and deletion has been shown. E1AF is an ets-oncogene family transcription factor, and has been shown to upregulate multiple matrix metalloproteinase (MMP) genes that contribute to the malignant phenotype of cancer cells by inducing invasive and metastatic activities. EWS/ETS fusions are frequently observed in Ewing's sarcoma, and we have revealed that EWS/ETS chimeric protein activates telomerase activity by upregulating human telomerase reverse transcriptase (hTERT), but the transcriptional activation of hTERT by EWS/ETS was indirect, and EWS/ETS was seen to function as a co-activator for TERT transcription. A number of oncogenes and cancer-related genes contain AU-rich element (ARE) in non-coding regions of transcribed mRNA. HuR is a RNA-binding protein that has the potential to stabilize ARE-containing mRNAs. HuR is known to shuttle between the nucleus and the cytoplasm via several export pathways. When normal cells are exposed to stress, HuR is exported to the cytoplasm in a chromosome maintenance region 1 (CRM1)-dependent manner. However, we demonstrate that HuR is CRM-1 independently exported to the cytoplasm in oral cancer cells. ARE-mRNAs were also exported to the cytoplasm and stabilized in the oral cancer cells, which were inhibited by HuR knockdown. These findings suggest that transcriptional and translational abnormalities of oncogenes may contribute to the carcinogenesis of oral epithelial cells.