Background: The human genome contains a large number of repetitive elements including endogenous retroviruses and long interspersed nuclear elements (LINE). Repetitive elements have been shown to be activated and influence gene expression in Hodgkin lymphoma (HL). Some repetitive elements contain open reading frames that encode a reverse transcriptase. We analyzed RT activity and expression of reverse transcriptase sequences in HL cells.
Methods: RNA seq analysis was used for the identification of expressed putative reverse transcriptases in HL cells. Reverse transcriptase activity in HL cells was assessed using phage MS2 RNA as template for reverse transcription and amplification by quantitative polymerase chain reaction. Sensitivity of HL cells for the non-nucleoside reverse transcriptase inhibitor efavirenz was analyzed by flow cytometry. LINE-1 reverse transcriptase sequences were amplified from HL cell line L-428 by reverse transcription-polymerase chain reaction, cloned into vector pGEM-T Easy and sequenced by Sanger sequencing.
Results: HL cells showed high reverse transcriptase activity in comparison to normal blood cells. In addition, efavirenz killed HL cells in a dose dependent manner. RNA seq analysis suggested that HL cells express sequences corresponding to LINE-1 reverse transcriptase. By RT-PCR using LINE-1 reverse transcriptase specific primers, several transcripts containing open reading frames with predicted coding capacity for reverse transcriptase molecules were identified.
Conclusions: HL cells express LINE-1 reverse transcriptase sequences that might be responsible for the observed reverse transcriptase activity of these cells. LINE-1 reverse transcriptase might be interesting targets for future therapeutic developments.
Our work is supported by Mitteldeutsche Kinderkrebsforschung.