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G.L. Stewart

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    O12 - Lung Cancer Biology II (ID 87)

    • Event: WCLC 2013
    • Type: Oral Abstract Session
    • Track: Biology
    • Presentations: 1
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      O12.03 - Pseudogenes as miRNA sponges in non-small cell lung cancer (ID 3455)

      10:30 - 12:00  |  Author(s): G.L. Stewart

      • Abstract
      • Presentation
      • Slides

      Lung cancer is the most common cause of cancer death worldwide, with a five-year survival of less than 15%. This poor therapeutic outcome is largely due to complex molecular backgrounds as well as typically late stage at diagnosis, with most patients presenting with unresectable local tumours or metastatic disease. While mutations of driver genes is a well known mechanism of tumorigenesis, approximately half of all non-small cell lung cancer (NSCLC) tumours harbour no known actionable oncogenic drivers, emphasizing the need to explore alternative mechanisms. New sequencing technologies have allowed investigation of previously unexplored areas of the genome and revealed that several classes of non coding RNAs (ncRNAs), those with no protein product, are involved in tumourigenesis, emphasizing the need for further exploration and study. MicroRNAs (miRNAs) have emerged as major players in lung carcinogenesis, displaying both oncogenic and tumor suppressive functions through translational inhibition of genes containing miRNA target sequences. Pseudogenes are non-coding relatives of protein-coding genes that contain a high degree of sequence similarity with their parent genes, thus sharing many of the same miRNA target sequences. As a result, when overexpressed, a pseudogene can function as a miRNA "decoy" protecting its parent gene from miRNA-mediated translational inhibition. DNA copy number (CN) alterations (gain of oncogenes/loss of tumour suppressors), is a major molecular mechanism driving cancer. Like protein coding genes, CN alterations can influence ncRNA expression levels, and several pseudogenes have been reported to be deregulated at the CN level in other cancer types. We hypothesize that pseudogenes of lung cancer-related genes are deregulated at the CN level in NSCLC.

      Global CN profiles for 83 lung adenocarcinomas, and 12 squamous cell carcinomas, as well as paired adjacent non-malignant tissues were generated on the Affymetrix SNP 6.0 array. Frequencies of DNA CN alterations were assessed at candidate pseudogene loci (gain>2.3 copies, loss<1.7 copies). Candidate pseudogenes (1) have a parent gene that has been previously reported to play a role in cancer biology, (2) are expressed in human tissue, and (3) share at least one conserved miRNA binding site with its parent gene.

      Several pseudogenes for OCT4 (octamer-binding transcription factor 4), an early embryonic transcription factor, were found to be frequently gained (46.9-34.9%), and could protect OCT4 from miRNA-mediated translational inhibition. Additionally, pseudogenes for E2F3 (E2F Transcription Factor 3), a potent cell cycle regulator, as well as those for the well known lung cancer oncogene BRAF, were found to have high frequencies of CN alteration (36.1%, and 19.2%, respectively). These high frequencies of alteration suggest that these pseudogenes play an important role in NSCLC.

      These results suggest that pseudogenes are clonally selected for at the DNA level, and pseudogene-mediated protection of oncogenic transcripts from miRNA-mediated translational inhibition may represent a novel mechanism of oncogenicity in NSCLC. Analyses of pseudogene expression and corresponding parent gene protein level in cell models will yield insight into how this class of ncRNA affects tumourigenesis, potentially leading to improvements in early detection, diagnosis, and treatment.

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