IRE1α is critical for kaempferol induced neuroblastoma differentiation

Neuroblastoma is an embryonic malignancy arises out of the neural crest cells of the sympathetic nervous system. It is the most common childhood tumor and well known for its spontaneous regression via the process of differentiation. The induction of differentiation using small molecule modulators such as all trans retinoic acid is one of the treatment strategies to treat the residual disease. In this study, we have reported the effect of kaempferol, a phytoestrogen 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 on understanding the molecular mechanism of action showed that the activity of kaempferol happened through the activation of the endoribonuclease activity of IRE1α (Inositol requiring enzyme 1 alpha), an endoplasmic reticulum (ER) resident transmembrane protein. The in silico docking analysis and biochemical assays using recombinant human IRE1α confirms the binding of kaempferol to the ATP binding site of IRE1α and thereby activating ribonuclease activity. Treatment of cells with the small molecule inhibitor STF083010 which specifically targets and inhibits the endoribonuclease activity of IRE1α showed reduced expression of neuron specific markers and curtailed neuritogenesis. The knock down of IRE1α using plasmid based shRNA lentiviral particles also showed diminished changes in the change in morphology of the cells upon kaempferol treatment. Thus our study suggests that kaempferol induces differentiation of neuroblastoma cells via the IRE1α-XBP1 pathway.