IRE1α is critical for kaempferol induced neuroblastoma differentiation.

Neuroblastoma is an embryonic malignancy that arises out of the neural crest cells of the sympathetic nervous system. It is the most common childhood tumor known for its spontaneous regression via the process of differentiation. The induction of differentiation using small molecules such as retinoic acid is one of the therapeutic strategies to treat the residual disease. In this study, we have reported the effect of kaempferol in inducing differentiation of neuroblastoma cells in vitro. Treatment of neuroblastoma cells with kaempferol reduced the proliferation and enhanced apoptosis along with the induction of neuritogenesis. Analysis of the expression of neuron-specific markers such as β-III tubulin, neuron-specific enolase and NRDG1 (N-myc down-regulated gene 1) revealed the process of differentiation accompanying kaempferol-induced apoptosis. Further analysis to understand the molecular mechanism of action showed that the effect of kaempferol is mediated by the activation of the endoribonuclease activity of IRE1α (Inositol-requiring enzyme 1 alpha), an endoplasmic reticulum (ER) resident transmembrane protein. In silico docking analysis and biochemical assays using recombinant human IRE1α confirm the binding of kaempferol to the ATP binding site of IRE1α, which thereby activates IRE1α ribonuclease activity. Treatment of cells with the small molecule STF083010, which specifically targets and inhibits the endoribonuclease activity of IRE1α, showed reduced expression of neuron-specific markers and curtailed neuritogenesis. The knockdown of IRE1α using plasmid-based shRNA lentiviral particles also showed diminished changes in the morphology of the cells upon kaempferol treatment. Thus, our study suggests that kaempferol induces differentiation of neuroblastoma cells via the IRE1α -XBP1 pathway. This article is protected by copyright. All rights reserved.