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Splicing of a human endogenous retrovirus to a novel phospholipase A2 related gene
A E Feuchter-Murthy1, J D Freeman, D L Mager
1Terry Fox Laboratory, B.C. Cancer Agency, Vancouver, Canada.
Abstract:
As part of an investigation into the effects of endogenous retroviruses on adjacent genes, we have isolated a cDNA clone derived from the human teratocarcinoma cell line NTera2D1 representing a chimeric transcript in which an endogenous retrovirus-like element, RTVL-H, has been spliced to downstream cellular sequences. The 5' terminus of this clone, termed AF-5, occurs one bp downstream of the predicted transcriptional start site in the RTVL-H long terminal repeat (LTR). AF-5 contains an open reading frame of 689 amino acids beginning within RTVL-H sequences that has two domains of homology with phospholipase A2 (PLA2). These domains, of approximately 120 amino acids each, are 30-38% identical to secreted PLA2s and contain sequence features of both group I and II enzymes. The corresponding AF-5 transcript is 2.5 kb and is derived from a single copy novel gene termed PLA2L. Southern analysis indicates that the RTVL-H element is normally present in human DNA upstream of the PLA2L gene. RTVL-H/PLA2L chimeric transcripts were detected in two independent teratocarcinoma cell lines but not in several other cell lines or primary human tissues. Characterization of additional cDNA clones and PCR analysis indicates that multiple RTVL-H/PLA2L alternatively spliced transcripts are expressed. No evidence has been found for transcription from a non-LTR promoter. These findings strongly suggest that the endogenous LTR promotes expression of the human PLA2L gene in teratocarcinoma cells.
Insights
Endogenous retroviruses can activate adjacent genes. Researchers found a novel human gene, PLA2L, fused with a retroviral element (RTVL-H) in teratocarcinoma cells, suggesting LTR-driven gene expression.
Area of Science:
- Genomics
- Molecular Biology
- Retroviral Studies
Background:
- Endogenous retroviruses (ERVs) are remnants of ancient viral infections integrated into host genomes.
- The impact of ERVs on the regulation of adjacent cellular genes is an area of ongoing research.
- Teratocarcinoma cells offer a unique model for studying gene expression and differentiation.
Purpose of the Study:
- To investigate the effects of endogenous retroviruses on adjacent gene expression.
- To characterize a novel chimeric transcript involving an ERV and a cellular gene.
- To determine the role of the RTVL-H long terminal repeat (LTR) in gene activation.
Main Methods:
- cDNA cloning and sequencing from NTera2D1 teratocarcinoma cells.
- Southern blot analysis to determine gene structure and copy number.
- Polymerase Chain Reaction (PCR) to detect and analyze alternative splicing.
- Transcriptional analysis to identify promoter usage.
Main Results:
- A chimeric cDNA clone (AF-5) was isolated, representing a fusion of RTVL-H and downstream cellular sequences.
- AF-5 contains an open reading frame with homology to phospholipase A2 (PLA2), defining a novel gene PLA2L.
- RTVL-H/PLA2L chimeric transcripts were specifically detected in teratocarcinoma cell lines, not in other tissues.
- Alternative splicing of RTVL-H/PLA2L transcripts was observed, with no evidence of non-LTR promoter activity.
Conclusions:
- The RTVL-H long terminal repeat (LTR) acts as a promoter for the human PLA2L gene in teratocarcinoma cells.
- This study reveals a novel mechanism of gene regulation mediated by endogenous retroelements.
- The findings highlight the potential role of ERVs in shaping gene expression patterns during cellular differentiation or disease states.