20003 Background: Signaling through growth factor receptors is important in neuroblastoma pathogenesis. Chromosome 1p36 is commonly deleted in neuroblastoma tumors and is associated with a poor prognosis. UBE4B, a gene in 1p36, has been reported mutated in high- risk neuroblastoma. We have found a direct interaction between UBE4B and hrs, a protein required for epidermal growth factor receptor (EGFR) trafficking, suggesting a link between EGFR trafficking and neuroblastoma pathogenesis. We have analyzed the role of UBE4B in the EGFR pathway in neuroblastoma cell lines. Methods: The expression of UBE4B, hrs and EGFR were analyzed by quantitative Western blot in a panel of 7 human neuroblastoma cell lines (SHEP, SKNAS, SKNSH, KCNR, SY5Y, LA155N, NGP). EGFR degradation rates were determined by examining the kinetics of cellular EGFR depletion following a pulse of ligand. Results: UBE4B levels were lowest in SKNAS and highest in NGP cells. Hrs levels were lowest in SKNSH cells and higher in other cell lines. EGFR levels were lowest in NGP and KCNR and highest in SKNAS cells. UBE4B levels were correlated with known 1p deletions. EGFR degradation rates were slowest in SKNAS cells and therefore correlated with cellular UBE4B levels. The low degradation rates were correlated with high cellular levels of EGFR. Conclusions: Expression levels of UBE4B are correlated in neuroblastoma cell lines with chromosome 1p deletions. Cell lines with lower levels of UBE4B degrade EGFR at a markedly slower rate, correlated with higher cellular EGFR levels. We hypothesize that UBE4B affects cell growth by interacting with hrs, directing EGFR for degradation. In its absence the ability of a cell to sort growth factor receptors for degradation is inhibited, resulting in growth factor receptor overabundance and uncontrolled cell growth. These results support the testing of EGFR inhibitors in a future phase I trial for children with neuroblastoma. No significant financial relationships to disclose.
INSULIN-LIKE GROWTH FACTOR BINDING PROTHINS (IGFBPs) IN CONDITIONED MEDIUM FROM HUMAN NEUROBLASTOMA CELL LINES