Author of

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  P3.02 - Poster Session 3 - Novel Cancer Genes and Pathways (ID 149)

  • Event: WCLC 2013
  • Type: Poster Session
  • Track: Biology
  • Presentations: 1
  • Moderators:
  • Coordinates: 10/30/2013, 09:30 - 16:30, Exhibit Hall, Ground Level

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    P3.02-006 - Downregulation of the candidate tumor suppressor gene SIRPA induces senescence mediated by Rb and p27 and is associated with mutation of EGFR (ID 1074)

    09:30 - 09:30  |  Author(s): I. Valencia
    • Abstract

    Background
    The epidermal growth factor receptor (EGFR) signaling pathway is involved in numerous biological processes including proliferation and apoptosis, migration/invasion, and angiogenesis, and has emerged as one of the most important and frequently deregulated pathways in NSCLC. The discovery of oncogenic, activating mutations in the tyrosine kinase domain of EGFR and DNA amplification of EGFR have led to the development of multiple targeted therapeutics against this pathway. While effective at prolonging survival, these targeted therapies are only applicable to a subset of patients (~15-20%) that harbour these alterations and resistance to treatment ultimately develops. As multiple genomic and epigenomic mechanisms can disrupt genes, a comprehensive understanding of the genetic alterations affecting genes within this pathway is required. An integrative, multi-dimensional genomics approach can detect genes disrupted by multiple mechanisms which may otherwise be overlooked if only a single genomic dimension were assessed, improving the ability to identify causal genetic events and decipher downstream consequences.

    Methods
    A multi-dimensional integrative analysis of copy number, DNA methylation and gene expression profiles on 77 adenocarcinomas and matched non-malignant tissue, was performed to investigate the complement of genetic alterations affecting the EGFR pathway. Novel candidate genes were validated in external datasets and immunohistochemical analysis of a tissue microarray was used to verify disruption at the protein level and to correlate expression with clinical features. The tumor suppressive effects of SIRPA were assessed by stable knockdown and in vitro assays on a panel of lung cancer cell lines. The effect of SIRPA downregulation on TKI sensitivity was assessed by dose response assays.

    Results
    Of the 35 genes examined, 11 were aberrantly expressed in over 50% of tumors, with 6 (RRAS, SIRPA, PIK3R1, TGFA, ERBB2 and EGFR) ranking in the 95th percentile of altered genes. Of these genes, all but SIRPA are known to be frequently disrupted in NSCLC and play a role in tumorigenesis. SIRPA is a transmembrane protein that negatively regulates receptor tyrosine kinsase activity and is frequently downregulated at both the mRNA and protein level in NSCLC tumors and cell lines. Underexpression of SIRPA is associated with EGFR mutations and is more prominent in adenocarcinoma than squamous cell carcinoma. Downregulation of SIRPA enhanced colony formation and wound healing but impaired viability and suppressed proliferation. Interestingly, SIRPA knockdown induced a senescent phenotype through the accumulation of p27 and Rb in its unphosphorylated state thereby blocking progression of the cell cycle. These results suggest senescence induced by SIRPA downregulation is a tumor suppressive mechanism that must be overcome to develop tumors.

    Conclusion
    Our integrative analysis of the EGFR pathway revealed SIRPA as one of the most frequently deregulated genes within the pathway. SIRPA functions as a tumor suppressor gene, controlling a number of biological functions through the inhibition of singaling pathways downstream of EGFR. To our knowledge, this is the first study to report a role for SIRPA in NSCLC tumorigenesis.