BMI1 facilitates Wnt signaling by epigenetic silencing of Axin2 to promote cell proliferation and migration in Hirschsprung's disease.

Hirschsprung's disease (HSCR) is a congenital intestinal disease characterized by the loss of enteric neural crest cells. BMI1 is demonstrated to be downregulated in HSCR tissues compared to normal intestinal tissues, but it is still unclear whether BMI1 is involved in the pathogenesis of HSCR. Here, we found that BMI1 expression was downregulated in HSCR-stenosed segments (HSCR-S) cases compared with HSCR-dilated segments (HSCR-D) or control cases. Pharmacological inhibition of BMI1 using PTC-209 significantly attenuated cell proliferation, migration, and cell cycle progression in both SH-SY5Y neuroblastoma cells and primary enteric neural crest cells (ENCCs), whereas BMI1 overexpression produced the opposite effects. BMI1 binds to the promoter region of the Wnt signaling pathway inhibitor Axin2 and suppressed its transcription by increasing H2AK119ub and reducing H3K4me3 at the Axin2 promoter, thereby hindering Wnt signaling. Moreover, overexpression of Axin2 decreased cell proliferation, migration and cell cycle progression. Treatment with HY-122816 (a Wnt signaling pathway agonist) reversed the inhibitory effects of PTC-209 on cell proliferation, migration, and cell cycle progression. Additionally, BMI1 upregulation promoted ganglion cell proliferation in Ednrb-/- mice. In conclusion: BMI1 facilitated Wnt signaling by mediating epigenetic silencing of Axin2, thereby promoting cell proliferation and migration in HSCR. Clinically, BMI1 expression was downregulated in HSCR-S cases compared with HSCR-D or control cases. Moreover, BMI1 was shown for the first time to promote cell proliferation, migration, and cell cycle progression in ENCCs. Molecular level probing revealed that BMI1 binds to the promoter region of Axin2, an inhibitor of the Wnt signaling pathway, and inhibited Axin2 transcription by increasing H2AK119ub and decreasing H3K4me3 in the Axin2 promoter, thereby hindering Wnt signaling. This study revealed that the BMI1/Axin2/Wnt axis may play an important role in the pathogenesis of HSCR.