| Summary: | <p>Abstract</p> <p>Background</p> <p>Neuroblastoma is a frequently lethal pediatric cancer in which <it>MYCN </it>genomic amplification is highly correlated with aggressive disease. Deregulated <it>MYC </it>genes require co-operative lesions to foster tumourigenesis and both direct and indirect evidence support activated <it>Ras </it>signaling for this purpose in many cancers. Yet <it>Ras </it>genes and <it>Braf</it>, while often activated in cancer cells, are infrequent targets for activation in neuroblastoma. Recently, the <it>Ras </it>effector <it>PIK3CA </it>was shown to be activated in diverse human cancers. We therefore assessed <it>PIK3CA </it>for mutation in human neuroblastomas, as well as in neuroblastomas arising in transgenic mice with <it>MYCN </it>overexpressed in neural-crest tissues. In this murine model we additionally surveyed for <it>Ras </it>family and <it>Braf </it>mutations as these have not been previously reported.</p> <p>Methods</p> <p>Sixty-nine human neuroblastomas (42 primary tumors and 27 cell lines) were sequenced for <it>PIK3CA </it>activating mutations within the C2, helical and kinase domain "hot spots" where 80% of mutations cluster. Constitutional DNA was sequenced in cases with confirmed alterations to assess for germline or somatic acquisition. Additionally, <it>Ras </it>family members (<it>Hras1</it>, <it>Kras2 </it>and <it>Nras</it>) and the downstream effectors <it>Pik3ca </it>and <it>Braf</it>, were sequenced from twenty-five neuroblastomas arising in neuroblastoma-prone transgenic mice.</p> <p>Results</p> <p>We identified mutations in the <it>PIK3CA </it>gene in 2 of 69 human neuroblastomas (2.9%). Neither mutation (R524M and E982D) has been studied to date for effects on lipid kinase activity. Though both occurred in tumors with <it>MYCN </it>amplification the overall rate of <it>PIK3CA </it>mutations in <it>MYCN </it>amplified and single-copy tumors did not differ appreciably (2 of 31 versus 0 of 38, respectively). Further, no activating mutations were identified in a survey of <it>Ras </it>signal transduction genes (including <it>Hras1</it>, <it>Kras2</it>, <it>Nras</it>, <it>Pik3ca</it>, or <it>Braf </it>genes) in twenty-five neuroblastic tumors arising in the <it>MYCN-</it>initiated transgenic mouse model.</p> <p>Conclusion</p> <p>These data suggest that activating mutations in the Ras/Raf-MAPK/PI3K signaling cascades occur infrequently in neuroblastoma. Further, despite compelling evidence for <it>MYC </it>and <it>RAS </it>cooperation in vitro and in vivo to promote tumourigenesis, activation of <it>RAS </it>signal transduction does not constitute a preferred secondary pathway in neuroblastomas with <it>MYCN </it>deregulation in either human tumors or murine models.</p>
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