# LINE-1 genotoxicity and cytotoxicity and its relevance to cancer

> **NIH NIH F30** · JOHNS HOPKINS UNIVERSITY · 2020 · $50,520

## Abstract

Project Summary
Half of human cancers overexpress a Long Interspersed Element-1 (LINE-1, L1) encoded protein, open
reading frame 1 protein (ORF1p). Though typically silenced by CpG methylation in somatic cells, L1 promoters
become hypomethylated in human cancers, ultimately leading to a `reawakening' that generates somatic L1
insertions into cancer genomes. This has been described in many types of gastrointestinal tract cancers, as
well as lung and ovarian cancers. L1 retrotransposition (RTn) requires ORF1p and a second protein, ORF2p,
which possesses endonuclease and reverse transcriptase activities. ORF2p endonuclease cleaves target site
DNA and reverse transcriptase copies L1 RNA into the genome in a process known as target primed reverse
transcription (TPRT). ORF2p endonuclease activity is associated with double-strand breaks (DSBs) in cultured
cells, and L1 expression is cytotoxic in cell culture. This proposal seeks to reconcile the growth deficits induced
by L1 overexpression in vitro with the prevalent expression of ORF1p in malignant cells in vivo. I hypothesize
that expression of L1 results in ORF2p nucleolytic activity that causes DSBs in both cultured cells and in
cancers. Further, ORF2p-generated DSBs induce cytotoxicity in non-transformed cells. Aim 1 proposes to map
loci in the genome bound by ORF2p and provide evidence for ORF2p-mediated DSBs at these sites,
establishing a direct link between L1 expression and DNA damage. Aim 2 seeks to elucidate the genetic
determinants of cellular fitness in L1-expressing cells and is broken down into two parts. Aim 2A tests the
hypothesis that p53 restricts RTn and survival in non-transformed cells expressing L1. Aim 2B will identify
genes contributing to L1 toxicity by implementing an unbiased genome-wide knockout screen, and includes a
rigorous validation strategy. Together, these studies will provide insights into the mechanisms that enable
cancer cell survival and proliferation in the face of L1 expression.

## Key facts

- **NIH application ID:** 9843115
- **Project number:** 5F30CA221175-03
- **Recipient organization:** JOHNS HOPKINS UNIVERSITY
- **Principal Investigator:** Daniel Ardeljan
- **Activity code:** F30 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $50,520
- **Award type:** 5
- **Project period:** 2018-01-01 → 2020-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9843115

## Citation

> US National Institutes of Health, RePORTER application 9843115, LINE-1 genotoxicity and cytotoxicity and its relevance to cancer (5F30CA221175-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9843115. Licensed CC0.

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