LINE-1 and Alu Promote Breast Tumor Progression Via Forming Chimeric Transcripts

Background：LINE-1 (L1) and Alu were reported to regulate tumor development and progression by constituting chimeric transcripts with diverse sequences. The landscape of L1 or Alu chimeric transcripts in breast tumor has not been reported yet, so breast tumor L1 and Alu chimeric transcripts were investigated in this study by analyzing more than 50 billion RNA sequences of breast tumor tissues and adjacent normal tissues from TCGA database. Results：The expression of L1 and Alu in breast tumor tissues were significantly higher than that in the non-tumor tissues. High expression of L1 and Alu in breast tumor predicted poor prognosis. Further exploration demonstrated that L1 and Alu were extensively chimerically expressed with adjacent transcripts. 651 L1-mRNA chimeric transcripts and 1525 Alu-mRNA chimeric transcripts showed significantly different frequencies between non-tumor and tumor tissues. 1009 L1-lncRNA chimeric transcripts and 2575 Alu-lncRNA chimeric transcripts had significantly different frequencies between non-tumor and tumor tissues. Function cluster analysis demonstrated that these differently chimerically expressed genes were involved in multi facets of tumorigenesis, including metabolism, signal transduction, immune reaction, cell cycle and apoptosis, etc. Conclusions：Chimeric expression with different sequences might be an important mechanism for L1 and Alu to promote breast tumor progression.