| Summary: | 碩士 === 國立成功大學 === 分子醫學研究所 === 104 === Neuroblastoma is an embryonic tumor arising from neural crest cells that fail to differentiate into the sympathetic nervous system. Encoded by the nm23-H1 gene, human NDPK-A acts as a metastasis promoter in neuroblastoma. However, its molecular mechanism is largely unknown. Our lab has found that NDPK-A binds to nuclease hypersensitive element (NHE) III1 in the c-myc promoter and down-regulates the c-myc promoter activity in neuroblastoma NB69 and non-neuroblastoma HeLa cells. In addition, an element upstream of NHE III1 in the c-myc promoter is also involved in NDPK-A mediated down-regulation of c-myc transcription. Based on the cDNA microarray data in our lab, FBP-1 was identified as a potential collaborator of NDPK-A since it is known to bind to a single-stranded far upstream element (FUSE) in the c-myc promoter and activates c-myc transcription. In this study, knocking down NDPK-A expression increased c-myc transcription and FBP-1 expression in neuroblastoma SH-SY5Y cells. On the other hand, knockdown of FBP-1 expression reduced the c-myc promoter activity, and the latter was further decreased by ectopic NDPK-A expression in NB69 and SH-SY5Y cells. Moreover, the expression of c-myc, FBP-1 and nm23-H1 was down-regulated during neuronal differentiation of SH-SY5Y cells as induced by retinoic acid (RA). Although knockdown of FBP-1 expression increased RA-induced neuronal differentiation of SH-SY5Y cells, knockdown of NDPK-A expression decreased such differentiation. RA-induced neuronal differentiation was increased by ectopic expression of NDPK-A, but failed to be further elevated by knocking down FBP-1 expression. Furthermore, ectopic NDPK-A also abrogated neuronal differentiation of SH-SY5Y cells enhanced by knocking down the expression of candidates in the NDPK-A network, such as HOXA9, RIN2, and RIT2. It is known that c-Myc participates in neural crest development in Xenopus. Based on whole mount in-situ hybridization, nme2b1 (a highly homologous nm23-H1 ortholog) and myca (a c-myc ortholog) transcripts were spatially and temporally co-localized during early development of zebrafish, indicating a potential role of NME2b1 in regulating myca transcription. In conclusion, FBP-1 was involved in NDPK-A mediated regulation of c-myc transcription and neuronal differentiation. By deregulating c-myc transcription, metastasis-associated NDPK-A overexpression likely arrest neural crest at its migratory/invasive stage during differentiation into sympathetic neurons, thereby leading to aggressive neuroblastoma.
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