Retinoic acid–induced survival effects in SH‐SY5Y neuroblastoma cells

Neuroblastoma is a malignant childhood cancer arising from the embryonic sympathoadrenal lineage of the neural crest. Retinoic acid (RA) is included in the multimodal therapy of patients with high‐risk neuroblastoma to eliminate minimal residual disease. However, the formation of RA‐resistant cells substantially lowers 5‐year overall survival rates. To examine mechanisms that lead to treatment failure, we chose human SH‐SY5Y cells, which are known to tolerate incubation with RA by activating the survival kinases Akt and extracellular signal‐regulated kinase 1/2. Characterization of downstream pathways showed that both kinases increased the phosphorylation of the ubiquitin ligase mouse double minute homolog 2 (Mdm2) and thereby enhanced p53 degradation. When p53 signaling was sustained by blocking complex formation with Mdm2 or enhancing c‐Jun N‐terminal kinase (JNK) activation, cell viability was significantly reduced. In addition, Akt‐mediated phosphorylation of the cell‐cycle regulator p21 stimulated complex formation with caspase‐3, which also contributed to cell protection. Thus, treatment with RA augmented survival signaling and attenuated basal apoptotic pathways in SH‐SY5Y cells, which increased cell viability. Our results show in the SH‐SY5Y neuroblastoma cell model how terminal differentiation and cell‐cycle arrest in response to retinoic acid can be prevented by neuroblastoma cells. Using the Akt and extracellular signal‐regulated kinase 1/2 pathways to control p53 and (phospho‐)p21 levels, SH‐SY5Y cells can carefully balance pro‐ and anti‐apoptotic signals to ensure their survival.