Abstract 2963: ALK is a MYCN target gene and contributes to cell growth, migration and invasion in neuroblastoma

Abstract

Abstract Neuroblastoma (NBL), the most common solid tumor of childhood, is an embryonal malignancy of the developing sympathetic nervous system. Human Anaplastic lymphoma kinase (ALK) has been identified as an oncogene mutated or amplified in NBLs. However, the role of wild-type ALK in NBL is still largely unknown. For better understanding a molecular event associated with ALK in the pathogenesis of NBL, it is necessary to clarify how ALK gene contributes to NBL progression. Previously in the analysis of NBL clinical samples, we have found that ALK expression is significantly high in MYCN amplified group. Consistent with this evidence, the developing tumors with NBL characteristics in MYCN-transgenic mice possess a high expression of ALK. In the present study, we have found that overexpression of MYCN induced ALK expression and siRNA-mediated knockdown of MYCN resulted in the downregulation of ALK expression in NBL and non-NBL cell lines. We have identified the promoter region of ALK, to which MYCN binds, in the upstream of the first exon from +30 to −350 bp and Luciferase reporter assay showed that MYCN overexpression enhanced the promoter activity of ALK. The site-specific deletion at MYCN binding site of ALK promoter region downregulated its promoter activity and chromatin immunoprecipitation (ChIP) assay indicated that MYCN can be recruited to the ALK promoter region, suggesting that ALK is directly regulated by MYCN. In general, high expression of MYCN is a well-known prognostic marker for aggressive progression and increases growth rate of NBL cells. However, the role of MYCN in enhancing cell migration and invasion has not yet been fully understood. We have further examined an effect of ALK expression in MYCN-induced cell migration. Functional assay revealed that overexpression of ALK enhanced NBL cell growth, migration as well as invasion. Moreover, these activities were suppressed by siRNA-mediated knockdown of ALK, indicating that ALK might be involved in the metastatic phenotype of NBLs. On the other hand, the forced expression of MYCN enhanced cell migration in MYCN-single copy cell line, SK-N-AS cells. Of interest, the increased migration by MYCN expression was suppressed by siRNA-mediated knockdown of ALK, suggesting that the cell migration induced by MYCN is at least partly regulated by ALK expression. Our present findings explore the fundamental understanding of ALK and help a future development of novel therapeutic tools by targeting ALK for aggressive NBLs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2963. doi:1538-7445.AM2012-2963