LINE-1 ORF2p expression is nearly imperceptible in human cancers.

{"sci_version": "1.2", "schema": "https://corpus.bntrg.co.uk/sci/1.0/sci.schema.json", "id": "pmid:31892958", "kind": "science-record", "revision": 7, "content_hash": "sha256:d50cc47d9dbf7cada0c3fc743c2bb0b8feb6915866182605615779564ac856fd", "created_at": "2026-11-01T15:40:54Z", "updated_at": "2026-11-01T22:01:09Z", "generator": {"name": "corpus-assay-engine", "run_id": "reading-sci-2026-11-01"}, "paper": {"state": "complete", "title": "LINE-1 ORF2p expression is nearly imperceptible in human cancers.", "doi": "10.1186/s13100-019-0191-2", "pmid": "31892958", "authors": ["Daniel Ardeljan", "Xuya Wang", "Mehrnoosh Oghbaie", "Martin S Taylor", "David Husband", "Vikram Deshpande", "Jared P Steranka", "Mikhail Gorbounov", "Wan Rou Yang", "Brandon Sie", "H Benjamin Larman", "Hua Jiang", "Kelly R Molloy", "Ilya Altukhov", "Zhi Li", "Wilson McKerrow", "David Fenyö", "Kathleen H Burns", "John LaCava"], "journal": "Mobile DNA", "year": 2020, "abstract": "BACKGROUND: Long interspersed element-1 (LINE-1, L1) is the major driver of mobile DNA activity in modern humans. When expressed, LINE-1 loci produce bicistronic transcripts encoding two proteins essential for retrotransposition, ORF1p and ORF2p. Many types of human cancers are characterized by L1 promoter hypomethylation, L1 transcription, L1 ORF1p protein expression, and somatic L1 retrotransposition. ORF2p encodes the endonuclease and reverse transcriptase activities required for L1 retrotransposition. Its expression is poorly characterized in human tissues and cell lines.\nRESULTS: We report mass spectrometry-based tumor proteome profiling studies wherein ORF2p eludes detection. To test whether ORF2p could be detected with specific reagents, we developed and validated five rabbit monoclonal antibodies with immunoreactivity for specific epitopes on the protein. These reagents readily detect ectopic ORF2p expressed from bicistronic L1 constructs. However, endogenous ORF2p is not detected in human tumor samples or cell lines by western blot, immunoprecipitation, or immunohistochemistry despite high levels of ORF1p expression. Moreover, we report endogenous ORF1p-associated interactomes, affinity isolated from colorectal cancers, wherein we similarly fail to detect ORF2p. These samples include primary tumors harboring hundreds of somatically acquired L1 insertions. The new data are available via ProteomeXchange with identifier PXD013743.\nCONCLUSIONS: Although somatic retrotransposition provides unequivocal genetic evidence for the expression of ORF2p in human cancers, we are unable to directly measure its presence using several standard methods. Experimental systems have previously indicated an unequal stoichiometry between ORF1p and ORF2p, but in vivo, the expression of these two proteins may be more strikingly uncoupled. These findings are consistent with observations that ORF2p is not tolerable for cell growth.", "claims": [{"id": "claim-method", "statement": "(a) For tumor A, we performed t-tests between anti-ORF1p IPs and IgG-controls. For tumor B and C, we performed t-tests between tumor and normal tissue after anti-ORF1p IP, as well as between tumor anti-ORF1p IPs and IgG-controls. (b) Adjusted p-values were calculated using Benjamin-Hochberg method.", "kind": "methodological", "target": null, "evidence": [{"asset": "source:pmid:31892958", "locator": "sections[30] \"Variance Analysis\" paragraph 2", "quote": "(a) For tumor A, we performed t-tests between anti-ORF1p IPs and IgG-controls. For tumor B and C, we performed t-tests between tumor and normal tissue after anti-ORF1p IP, as well as between tumor anti-ORF1p IPs and IgG-controls. 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RESULTS: We report mass spectrometry-based tumor proteome profiling studies where", "y of data and materials Proteomics data. The mass spectrometry proteomics data have been deposited to the P", "XD013743. Availability of data and materials Proteomics data. The mass spectrometry proteomics data", "rials Proteomics data. The mass spectrometry proteomics data have been deposited to the ProteomeXcha"], "order_basis": "paper_text_order:623", "id": "assay:1"}, {"role": "data_generation", "definition_id": "ihc", "definition_version": "99e1195c7d6f", "definition_digest": null, "required_operations": [], "support_state": "partial", "source_hashes": {"assay_lexicon": "99e1195c7d6f"}, "confidence": 0.99, "evidence": ["nes by western blot, immunoprecipitation, or immunohistochemistry despite high levels of ORF1p expression. Mor", "dated five rabbit monoclonal antibodies with immunoreactivity for specific epitopes on the protein. These"], "order_basis": "paper_text_order:842", "id": "assay:2"}, {"role": "data_generation", "definition_id": "western_blot", "definition_version": "99e1195c7d6f", "definition_digest": null, "required_operations": [], "support_state": "partial", "source_hashes": {"assay_lexicon": "99e1195c7d6f"}, "confidence": 0.99, "evidence": ["cted in human tumor samples or cell lines by western blot, immunoprecipitation, or immunohistochemistr", "e chart. Additional file 3: Figure S4. Co-IP/Western blot. Three different segments of Tumor D were us", "umor D co-IPs. Additional file 4: Figure S2. Western blot α-ORF1p titer to detect endogenous ORF1p in"], "order_basis": "paper_text_order:1065", "id": "assay:3"}, {"role": "data_generation", "definition_id": "animal_model", "definition_version": "99e1195c7d6f", "definition_digest": null, "required_operations": [], "support_state": "partial", "source_hashes": {"assay_lexicon": "99e1195c7d6f"}, "confidence": 0.99, "evidence": ["l stoichiometry between ORF1p and ORF2p, but in vivo, the expression of these two proteins may be", "1–3), including a mock-capture control using mouse IgG affinity medium with tumor extracts (mIg", "umor A-1 to A-6), and three replicates using mouse IgG-coupled affinity medium to sample non-sp", "s (Tumor B-1 to B-3), three replicates using mouse IgG-coupled affinity medium to sample non-sp"], "order_basis": "paper_text_order:1795", "id": "assay:4"}, {"role": "data_generation", "definition_id": "cell_culture", "definition_version": "99e1195c7d6f", "definition_digest": null, "required_operations": [], "support_state": "partial", "source_hashes": {"assay_lexicon": "99e1195c7d6f"}, "confidence": 0.77, "evidence": ["ORF1p signal is observed in all cases except HeLa Kyoto. 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