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R. Chari
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P1.02 - Poster Session with Presenters Present (ID 454)
- Event: WCLC 2016
- Type: Poster Presenters Present
- Track: Biology/Pathology
- Presentations: 1
- Moderators:
- Coordinates: 12/05/2016, 14:30 - 15:45, Hall B (Poster Area)
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P1.02-052 - Signal Regulatory Protein a (SIRPA): A Key Regulator of the EGFR Pathway Demonstrates Both Tumor Suppressive and Oncogenic Properties (ID 6061)
14:30 - 14:30 | Author(s): R. Chari
- Abstract
Background:
The epidermal growth factor receptor (EGFR) signaling pathway is one of the most frequently deregulated pathways in non-small cell lung cancer. While targeted therapy prolongs survival in patients harbouring EGFR mutations, resistance to treatment eventually develops in all cases. As multiple genetic and epigenetic alterations are known to disrupt signaling pathways, the objective of this study is to perform a multidimensional analysis of signaling pathways to identify alterations essential to tumorigenesis that are overlooked when assessing a single genomic dimension.
Methods:
Multidimensional integrative analysis of copy number, DNA methylation, and gene expression profiles of 77 lung adenocarcinomas and matched non-malignant tissues identified Signal Regulatory Protein A (SIRPA) as a novel candidate tumor suppressor gene. Following validation of genomic findings in multiple external data sets, the tumor suppressive effects of SIRPA were assessed in vitro and in vivo with a panel of lung cancer cell lines.
Results:
SIRPA negatively regulates receptor tyrosine kinase signaling through activation of the protein phosphatases SHP1 and SHP2 and was found to be underexpressed in 70% of lung tumours, ranking it in the 95[th] percentile of altered genes within the EGFR pathway. Immunohistochemistry (IHC) confirmed reduced protein expression in tumors, which was found to correlate with EGFR mutation and adenocarcinoma histology. In vitro, SIRPA knockdown promoted migration while simultaneously inducing a dramatic senescent phenotype, suggesting SIRPA may act as a barrier to tumorigenesis. This phenotype is dependent upon upregulation of the CDK inhibitor p27, which hypophosphorylates RB leading to cell cycle blockade and reduced tumor growth in vivo. Importantly, increased expression of p27 resulted in mis-localization into the cytoplasm where it is known to promote an invasive phenotype. Inhibition of p27 confirmed previous findings and emphasized the importance of this pathway in lung tumorigenesis. Surprisingly, overexpression of SIRPA increased cell growth and migration, suggesting SIRPA may also possess oncogenic properties due to its regulation of multiple signaling pathways. Overexpression of SHP2 following ectopic expression of SIRPA promotes migration through the inhibition of focal adhesions. This phenotype is abrogated upon siRNA knockdown of SHP2.
Conclusion:
SIRPA is an important player in lung tumor biology, capable of acting as both an oncogene and tumor suppressor due to its ability to regulate multiple signaling pathways. Due to the complex nature in its signaling, future work should focus on elucidating how the timing of alterations to SIRPA affects tumorigenesis to design treatment strategy.
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P3.01 - Poster Session with Presenters Present (ID 469)
- Event: WCLC 2016
- Type: Poster Presenters Present
- Track: Biology/Pathology
- Presentations: 1
- Moderators:
- Coordinates: 12/07/2016, 14:30 - 15:45, Hall B (Poster Area)
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P3.01-049 - ELF3 Overexpression Leads to Oncogenic Reprogramming of Protein Interactions Exposing Therapeutically Actionable Targets (ID 5807)
14:30 - 14:30 | Author(s): R. Chari
- Abstract
Background:
Emerging evidence has implicated ELF3 involvement in cancer signaling pathways. To determine the biological basis to pursue ELF3 as a novel therapeutic target, we investigated the role of ELF3 in lung adenocarcinoma (LUAD). Using a multi-omics approach in two independent cohorts of LUAD we (a) discover genetic mechanisms driving aberrant expression of this oncogene, (b) identify the protein-protein-interaction (PPI) partners of ELF3, and (c) determine the specific functions of ELF3 in LUAD using model systems.
Methods:
Comprehensive, multi-omic data was collected from the BC Cancer Research Centre (BCCRC), The Cancer Genome Atlas (TCGA), and several mouse models of LUAD tumourigenesis. ELF3 cellular localization was visualized by immunofluorescence. ELF3 knock-down and overexpression was achieved by lentiviral vector delivery for in vitro and in vivo assays. Physical protein-protein interaction (PPI) networks obtained from IID were overlaid onto cancer and non-malignant gene expression data from TCGA and 11 restructured datasets from Gene Expression Omnibus. PPIs were interrogated to investigate malignancy-associated ELF3 interactions. Pathway analysis was performed using pathDIP. Survival analysis was performed using the log-rank method.
Results:
ELF3 was significantly overexpressed in both cohorts, remarkably in >70% of cases (p=1.64E-21). However, mutation of known upstream regulators was not sufficient to explain the frequency of ELF3 overexpression. Instead, the ELF3 locus underwent frequent (>80%) genetic alteration including focal amplification and promoter hypomethylation, which corresponded with increased expression. ELF3 was predominantly localized to the nucleus, consistent with its transcription factor function. Analysis of PPI networks indicated highly LUAD-specific ELF3 interactions whereby loss and gain of interactions lead to reprogramming of LUAD transcriptional networks, including loss of TNFα pathway, and gain of TGFβ pathway, PI3K pathway, and translesion (DNA repair) pathway interactions. Furthermore, EGFR, KRAS, and MYC transgenic models of LUAD tumourigenesis all displayed a marked increase (6 to 8-fold) in ELF3 expression signifying its importance to LUAD of varied genetic backgrounds. In culture, ELF3 regulated proliferation, viability and anchorage-independent growth. In animal models, ELF3 knock-down cells underwent negative clonal selection, suggesting ELF3 expression is beneficial to tumour growth. Clinically, high expression of ELF3 was associated with poor survival regardless of tumour stage.
Conclusion:
Overexpression of ELF3 reprograms protein-protein-interactions in LUAD leading to the activation of cancer-specific pathways, and producing oncogenic phenotypes. Depletion of ELF3 with shRNAs reverses tumour cell growth, suggesting ELF3 is a promising therapeutic target. In addition to ELF3, interruption of cancer-specific PPIs also represents a therapeutically actionable strategy.
