Investigation of the Oncogenic Role of the Cell Cycle Regulator SAPCD2 in Pediatric Neuroblastoma

Abstract

Pediatric neuroblastoma is the most common extra‐cranial malignancy in infants and children. Neuroblastoma is a neuroendocrine cancer arising from sympathetic neuronal precursors that circumvent the differentiation process into mature neurons and glia. The poor differentiation status of neuroblastoma cells allows them to retain features of early embryonic stem cells. SAPCD2 is a newly identified cell cycle regulator involved in mitotic progression and spindle assembly. Although the mechanism by which SAPCD2 exerts its effect is poorly understood, its function appears to be critical in early embryonic development where it regulates mitotic spindle orientation, planar polarization in cell progenitors, and tissue segmentation. More relevant to this study, a recent investigation has revealed that SAPCD2 plays a role in symmetric planar divisions during early embryonic segmentation by interacting with the Gαi‐LGN‐NuMA ternary spindle assembly complex, which appears to be critically important for modulating differentiation of neuroepithelial cells. The expression of SAPCD2 is generally exclusive to embryonic tissues except in the case of malignancies where it is dramatically overexpressed compared to normal tissues. Its overexpression has been observed in several cancers such as in the lung and liver, but its relevance to neuroblastoma has not been reported in the current literature. The objective of this study is to investigate whether SAPCD2 expression levels in human neuroblastoma tissues are correlated with disease progression and if so, to further characterize its role in regulating neuroblastoma cell survival in vitro. The correlation of SAPCD2 with neuroblastoma patient survival was investigated using two data sets obtained from the public R2: Genomics database ( http://r2.amc.nl). The patients were divided into two groups based on SAPCD2 mRNA level (high or low), and the difference in patient survival between the two groups was compared using Kaplan‐Meier analysis. To further investigate the potential oncogenic role of SAPCD2 in vitro, the neuroblastoma cell line BE(2)‐C was transfected with siRNAs against SAPCD2 mRNA to determine the effect of SAPCD2 knockdown on neuroblastoma cell survival and proliferation. Our results demonstrate a statistically significant difference in the survival probabilities of neuroblastoma patients within the two SAPCD2 expression groups, with patients possessing high SAPCD2 mRNA levels showing significantly reduced survival compared to patients with low SAPCD2 mRNA level in both datasets. In in vitro experimental investigations, siRNA‐mediated knockdown of SAPCD2 caused a dramatic reduction in neuroblastoma cell viability after five days and a dramatic reduction in colony formation capacity after 14 days. These results strongly suggest that SAPCD2 functions as an oncogene in neuroblastoma and elevated SAPCD2 expression in neuroblastoma cells promote poor patient prognosis. Future elucidation of the role of SAPCD2 in contributing to the oncogenic transformation of neuroblastoma may ...