Together, these results suggest that KIF1B increases ROS, specifically O2, which is required for apoptosis and reinforcement of KIF1B protein expression in a positive feedback loop in neuroblastoma cells

Together, these results suggest that KIF1B increases ROS, specifically O2, which is required for apoptosis and reinforcement of KIF1B protein expression in a positive feedback loop in neuroblastoma cells. == Figure 4. Neuroblastoma SPL-B is the most common childhood extracranial solid tumor accounting for 10% of all pediatric cancers in the United States and 5. 3% of all pediatric SPL-B cancers in Singapore13. Due to its complexity, neuroblastoma can undergo regression and differentiation to become benign ganglioneuroma or oncogenic transformation into unfavorable metastatic tumors during diagnosis. High-risk neuroblastoma has been associated with chromosome 1p36 deletion4. Chromosome 1p36 contains a bonafide tumor suppressor gene called KIF1B which is likely to be involved and defective in various cancers including neuroblastoma5. KIF1B is a haploinsufficient 1p36 tumor suppressor and a downstream target of EglN3, which was found necessary and sufficient to mediate Nerve Growth Factor (NGF) withdrawal-induced apoptosis during neural crest development6, 7. Neuroblasts which are out-competed for NGF during SPL-B sympathetic nervous system development upregulate EglN3 to induce KIF1B, promote RNA Helicase A (DHX9) nuclear translocation and lead to apoptosis through increased XAF1 expression. Failure of developmental apoptosis due to loss of KIF1B may lead to improper survival of neuroblasts during NGF signaling phase of sympathetic nervous system development, predisposing tumorigenesis68. Previously, we have also showed that KIF1B protein expression does not always faithfully recapitulate patients 1p36 genotype. One out of two 1p36+/+and majority of 1p36+/neuroblastoma patients failed to express KIF1B protein6. Furthermore, given that EglN3-mediated increase in KIF1B protein expression is independent of transcription, the intermediate responsible for altering KIF1B protein expression remains unknown7. Separately, reactive oxygen species (ROS) has been well-studied for its role in various signaling pathways that are involved in key biological functions such as cell proliferation, differentiation and cell death9. Excessive ROS can induce oxidative stress, causing irreversible cell damage and cell death. On the other hand, slight increase of specific species may transiently promote biological changes involved in cell growth and differentiation. Thus, the biphasic and species-specific properties of ROS is important in determining cell fate10, 11. Altered cellular redox status is known to be implicated in tumorigenesis. Cancer cells often exhibit high metabolic activity that requires increased ATP to maintain biological processes such as uncontrolled proliferation. Increased ATP production is accompanied by increased ROS generation, leading to oxidative stress observed in most cancers. In order to cope with the oxidative burden, cancer cells increase their ROS-tolerating threshold by enhancing the expression of Rabbit Polyclonal to E-cadherin antioxidant enzyme9, 10. Furthermore, ROS-mediated genetic alterations and protein modifications may confer a survival advantage by creating a permissive environment for cancer cells to tolerate high ROS exposure. ROS also serves as secondary messengers in signaling cascades whereby it appears to be involved in transcriptional activation and other receptor-mediated signaling pathways9, 12, 13. Therefore , taking into consideration the multiple roles of ROS including cell death and protein modification, we SPL-B investigated the relationship between KIF1B and ROS. Specifically, given the recent role of KIF1B in mitochondrial dynamics and apoptosis, we asked if KIF1B could lead to ROS production and subsequent cell death14. Furthermore, we asked if ROS could be the missing intermediate in regulating KIF1B protein expression and thereby resolving the enigma of absent KIF1B protein expression in 1p36+/and 1p36+/+neuroblastoma patients. == Results == == Endogenous total ROS and O2levels correspond to KIF1B expression in neuroblastoma cells == To determine the correlation between ROS and KIF1B expression levels, endogenous total ROS and O2levels were measured across neuroblastoma cell lines with different KIF1B genotypic profiles based on their 1p36 status (Fig. 1A). The cell lines are NB1 (1p36/), CHP212 (1p36+/) SPL-B and SK-N-SH (1p36+/+). KIF1B-expressing cell line SK-N-SH has significantly higher ROS and O2levels compared.