核苷二磷酸激酶A(NDPK-A)在神經母細胞瘤中扮演著促進轉移的角色，此腫瘤發生於神經脊為常見的兒童癌症。在神經母細胞瘤後期病人中NDPK-A過度表現或其S120G突變(NDPK-AS120G)已被偵測到，NDPK-A表現的改變在in vitro中導致神經元分化的缺失且促進細胞侵略性，而在動物體中促進神經母細胞瘤轉移。然而截至目前NDPK-A如何參與在癌症轉移的過程中尚未釐清。c-myc在神經脊發育中扮演著必要的角色，NDPK-A和NDPK-B具有88%的高度相似性，而NDPK-B已知參與c-myc基因轉譯調控。因此在這次的研究中，將利用人類神經母細胞瘤NB69細胞株探討在人類神經母細胞瘤中NDPK-A及NDPK-B如何分別及共同調控c-myc轉譯。利用c-myc promoter部分去除的突變以及氯黴素乙醯機轉移酶分析(CAT assay)，發現在核酸酶高度敏感序列(NHE) III1 及NHE II具有負向順式調控片段 (cis-element)，而正向順式調控片段位於NHE II2上游。儘管NDPK-A 或NDPK-AS120G 並不顯著影響c-myc promoter的活性，但兩者在NB69所衍生出的暫時性及穩定性轉染細胞中都可藉由NHE III1及NHE II抑制c-myc 轉譯去抑制作用。另一方面，NDPK-B藉由NHE III1以外的順式調控片段顯著活化c-myc promoter的活性。然而在NB69細胞中，NDPK-A或NDPK-AS120G 消除了受NDPK-B影響所導致的c-myc轉譯活化現象。我目前的發現首次證明了NDPK-A在c-myc轉譯調控上扮演和NDPK-B不同的角色，實驗結果顯示在NB69細胞中NDPK-A可能以非傳統方式藉由NHE III1以及位於NHE II上尚未確認的順式調控片段調控c-myc轉譯。研究結果顯示NDPK-A的過度表現或S120G突變可能藉由不正常調控c-myc轉譯影響神經脊發育而引致轉移性神經母細胞瘤。

Nucleoside diphosphate kinase (NDPK)-A behaves as a metastasis promoter in neuroblastoma, which is a common childhood tumor arising from the neural crest. Overexpression or S120G mutation of NDPK-A have been detected in patients with advanced stages of neuroblastoma. Such NDPK-A alterations abrogate neuronal differentiation and enhance cell invasiveness in vitro, while promoting neuroblastoma metastasis in animals. Currently it is unclear how NDPK-A is involved in tumor metastasis. However, it is known that c-myc plays an essential role in neural crest development. NDPK-A shares 88% identity with NDPK-B and the latter participates in the regulation of c-myc transcription. In this study, I therefore examined the individual and collaborative effects of NDPK-A and NDPK-B on c-myc transcriptional regulation in the human neuroblastoma NB69 cell model. Using c-myc promoter deletion mutants and the CAT assay, I found that negatively regulatory cis-elements were present in nuclease hypersensitive element (NHE) III1 and II regions, whereas positively regulatory cis-elements localized to upstream of NHE II2. Although NDPK-A or NDPK-AS120G did not significantly affect c-myc promoter activity, either protein inhibited c-myc transcriptional derepression via NHE III1 and NHE II in NB69-derived transient and stable transfectants. On the other hand, NDPK-B significantly activated the c-myc promoter activity likely via cis-elements other than NHE III1. However, NDPK-B activated c-myc transcription was abrogated by NDPK-A or NDPK-AS120G in NB69 cells. My current findings provide the first evidence showing that NDPK-A plays a different role from NDPK-B in c-myc transcriptional regulation. My results suggest that NDPK-A may modulate c-myc transcription via NHE III1 and yet-to-be identified cis-elements in NHE II in a non-conventional fashion in NB69 cells. It is possible that overexpression or S120G mutation of NDPK-A deregulates c-myc transcription, which in turn may affect neural crest development and lead to metastatic neuroblastoma.

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