Data from High <i>Skp2</i> Expression Characterizes High-Risk Neuroblastomas Independent of <i>MYCN</i> Status

Abstract

<div>Abstract<p><b>Purpose:</b> Amplified <i>MYCN</i> oncogene defines a subgroup of neuroblastomas with poor outcome. However, a substantial number of <i>MYCN</i> single-copy neuroblastomas exhibits an aggressive phenotype similar to that of <i>MYCN</i>-amplified neuroblastomas even in the absence of high <i>MYCN</i> mRNA and/or protein levels.</p><p><b>Experimental Design:</b> To identify shared molecular mechanisms that mediate the aggressive phenotype in <i>MYCN</i>-amplified and single-copy high-risk neuroblastomas, we defined genetic programs evoked by ectopically expressed <i>MYCN in vitro</i> and analyzed them in high-risk versus low-risk neuroblastoma tumors (<i>n</i> = 49) using cDNA microarrays. Candidate gene expression was validated in a separate cohort of 117 patients using quantitative PCR, and protein expression was analyzed in neuroblastoma tumors by immunoblotting and immunohistochemistry.</p><p><b>Results:</b> We identified a genetic signature characterized by a subset of MYCN/MYC and E2F targets, including <i>Skp2</i>, encoding the F-box protein of the SCF<sup>Skp2</sup> E3-ligase, to be highly expressed in high-risk neuroblastomas independent of amplified <i>MYCN</i>. We validated the findings for <i>Skp2</i> and analyzed its expression in relation to <i>MYCN</i> and <i>E2F-1</i> expression in a separate cohort (<i>n</i> = 117) using quantitative PCR. High <i>Skp2</i> expression proved to be a highly significant marker of dire prognosis independent of both <i>MYCN</i> status and disease stage, on the basis of multivariate analysis of event-free survival (hazard ratio, 3.54; 95% confidence interval, 1.56-8.00; <i>P</i> = 0.002). Skp2 protein expression was inversely correlated with expression of p27, the primary target of the SCF<sup>Skp2</sup> E3-ligase, in neuroblastoma tumors.</p><p><b>Conclusion:</b> Skp2 may have a key role in the progression of neuroblastomas and should make an attractive target for therapeutic approaches.</p></div>