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OA 07 - Biomarker for Lung Cancer (ID 659)
- Event: WCLC 2017
- Type: Oral
- Track: Biology/Pathology
- Presentations: 1
- Moderators:Philip Christopher Mack, Shinichi Toyooka
- Coordinates: 10/16/2017, 15:45 - 17:30, Room 503
OA 07.07 - Inhibition of the Novel Oncogene ELF3 Abolishes Lung Adenocarcinoma Growth (ID 8408)
15:45 - 17:30 | Author(s): K. Ng
Oncogenic reactivation of transcription factors involved in fetal lung development is integral to lung adenocarcinoma (LUAD) biology, as observed with TITF1/NKX2-1 and the ETS transcription factors ETV4 and ETV5. ELF3 is an uncharacterized ETS family member implicated in fetal lung development encoded at 1q32.1. Interestingly, chromosome 1q is a region of frequent gain in LUAD that lacks a bona fide oncogene. We hypothesize that ELF3 is a novel oncogene and putative therapeutic target in LUAD.
Multiple independent datasets encompassing 1,685 clinical samples of LUAD, lung squamous cell carcinoma (LUSC), small cell lung cancer, and non-malignant lung tissues were analyzed to establish the frequency of ELF3 overexpression and underlying genetic mechanisms of selection. Protein-protein interaction (PPI) networks were constructed around ELF3, and integrated pathway analysis was performed to decipher the signaling network disruptions resulting from ELF3 overexpression. Isogenic cell lines were established to assess the ability of ELF3 to regulate oncogenic phenotypes. The effect of ELF3 loss on tumour growth was assessed in xenograft mouse models.
Strong ELF3 overexpression was frequently observed in LUAD (>2-fold: TCGA 40% p=1.5E-07; BCCA 73% p=1.6E-21), but was not observed in other lung cancer subtypes. Similarly, high ELF3 expression was significantly associated with poor overall survival of LUAD patients (all Stages p<0.0001, Stage I p<0.0001), but not LUSC patients (p>0.05). These clinical associations prompted further examination of ELF3 in the LUAD subtype of lung cancer. While mutations in ELF3 were rare, up to 80% of LUAD patients harboured focal amplification, DNA gain, and/or promoter hypomethylation at the ELF3 locus, which resulted in transcript overexpression. ELF3 overexpression induces remodeling of 23 direct PPI networks, resulting in loss of interaction with proteins such as MYC and GLI2, while forming new interactions with NKX2-1, HOXA5 and CDK8, among others. This reprogramming of PPI networks affects multiple oncogenic pathways including MAPK, TGF-beta and WNT. ELF3 knockdown in LUAD cell lines resulted in significantly reduced proliferation, viability, and anchorage-independent growth, demonstrating ELF3 has oncogenic properties. Loss of ELF3 abolished the ability of LUAD cells to establish tumours in xenograft mouse models, demonstrating the requirement of ELF3 expression for tumour growth.
ELF3 is a novel LUAD oncogene encoded on chromosome 1q, activated in up to 73% of patients, and strongly associated with poor overall survival. As ELF3 inhibition abolished tumour growth, therapeutic targeting of ELF3 could benefit LUAD patient outcome.
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P1.02 - Biology/Pathology (ID 614)
- Event: WCLC 2017
- Type: Poster Session with Presenters Present
- Track: Biology/Pathology
- Presentations: 1
- Coordinates: 10/16/2017, 09:30 - 16:00, Exhibit Hall (Hall B + C)
P1.02-006 - Arsenic Promotes Persistent Alterations in the Lung PiRNA Transcriptome to Target Epigenetic Pathways (ID 9567)
09:30 - 16:00 | Author(s): K. Ng
Chronic exposure to arsenic leads to the onset of different diseases, including lung cancer. Arsenic-induced lung tumors have been associated with a high-frequency of lung squamous-cell carcinomas among never smokers (a rare epidemiological pattern), suggesting a unique underlying biology. Epigenetic alterations are known to play a role in this process; however, detailed mechanisms are not yet fully elucidated. Piwi-interacting RNAs (piRNAs), a novel class of small non-coding RNAs (sncRNAs), play a key role in epigenetic regulation and maintenance of genome integrity. Here, we examine the impact of different arsenic species in the human piRNA transcriptome, using lung cell models mirroring chronic, low dose exposure. We also investigate the interaction network of deregulated piRNAs and identified biological pathways potentially affected.
One normal lung (HBEC) and two lung cancer cell lines: A459 (adenocarcinoma) and H520 (squamous-cell carcinoma) were grown in 10 ppm of sodium arsenite (AsIII) or arsenate (AsV) for six passages. Total RNA was extracted at different time points and sequenced. piRNA expression was deduced using our custom sncRNA analysis pipeline, which interrogates >23K piRNA-encoding human loci. piRNA/DNA binding prediction was performed using two different algorithms (miRanda/ThermoBLAST). Network analysis was performed using Partek Pathways.
Overall, 691 piRNAs were expressed. Persistent changes in piRNA expression over time were identified, with specific patterns associated with the different arsenic species. In HBECs (non-malignant lung tissue), 14 piRNAs were persistently upregulated and 16 downregulated in response to AsIII. Similarly, 6 were up- and 11 downregulated when the same cells were exposed to AsV. Only 1 piRNA, DQ598008, was commonly upregulated in response to both arsenic species, while 4 piRNAs were commonly downregulated. Lung cancer cell lines follow the same arsenic species-specific trends, with a high subtype-specificity indicating these species maintain a role during lung tumor development. Remarkably, we found an enrichment of genes associated with methyltransferase activities predicted to be targeted by piRNAs altered by AsIII (a biologically-relevant form of arsenic), evidencing their role in arsenic-related carcinogenic mechanisms.
Arsenic induces persistent alterations in the lung sncRNA transcriptome, particularly piRNAs, impacting pathways linked to epigenetic regulation. Together, these results provide insights into sncRNA-related mechanisms in arsenic-induced lung carcinogenesis. Moreover, different arsenic species induce distinct alteration patterns, highlighting the relevance of the source of exposure. piRNAs, as with other sncRNAs, are stable in biofluids, circulating tumour cells, and archival clinical materials. Therefore, piRNAs hold great promise as potential exposure and monitoring biomarkers for arsenic-related health effects.