OBJECTIVE To elucidate the molecular mechanism and the anti-breast cancer effect of polyphyllinⅠ,which is a natural compound extracted from Rhizoma of Paris polyphyllin.METHODS Human breast cancer cells were treated with polyphyllinⅠ,after which DRP1-dependent mitochondrial fission and apoptosis,mitophagy and PINK1/PARK2 pathway were evaluated.A genetic approach was employed to determine how knockdown of PINK1 with sh RNA regulates polyphyllinⅠ-induced mitophagy and apoptosis.The inhibitory effect of polyphyllinⅠon tumor growth in a breast cancer cell xenograft mouse model was also examined.RESULTS PolyphyllinⅠenhanced the stabilization of full-length PINK1at the mitochondrial surface,leading to PARK2 recruitment to mitochondria,and culminating in mitophagy.PolyphyllinⅠalso induced dephosphorylation of DRP1 at Ser637 and mitochondrial translocation of DRP1,leading to mitochondrial fission and apoptosis.Knockdown of PINK1 evidently suppressed mitophagy stimulated by polyphyllinⅠ,and markedly enhanced DRP1-dependent mitochondrial fission and apoptosis induced by polyphyl inⅠ.Furthermore,suppression of DRP1 by mdivi-1 or sh RNA inhibits PINK1 knockdown-mediated mitochondrial fragmentation and apoptosis in response to polyphyllinⅠtreatment,suggesting that depletion of PINK1 lead to mitochondrial fragmentation due to excessive fission.Our in vivo study also showed that knockdown of PINK1potentiated polyphyllinⅠ-mediated inhibition of tumor growth in a breast cancer cell xenograft mouse model.CONCLUSION Our study provides a mechanism to support the role of PINK1 in the regulation of polyphyl inⅠ-induced mitophagy and apoptosis,and suggest polyphylinⅠas a potential drug for treatment of breast cancer. OBJECTIVE To elucidate the molecular mechanism and the anti-breast cancer effect of polyphyllin I, which is a natural compound extracted from Rhizoma of Paris polyphyllin. METHODS Human breast cancer cells were treated with polyphyllin I, after which DRP1-dependent mitochondrial fission and apoptosis, mitophagy and PINK1 / PARK2 pathway were used. A genetic approach was employed to determine how knockdown of PINK1 with sh RNA regulates polyphyllin I-induced mitophagy and apoptosis. Inhibitory effect of polyphyllin Ion tumor growth in a breast cancer cell xenograft mouse model was also observed .RESULTS Polyphyllin enhances the stabilization of full-length PINK1at the mitochondrial surface, leading to PARK2 recruitment to mitochondria, and culminating in mitophagy. Polyphyllin Ialso induced dephosphorylation of DRP1 at Ser637 and mitochondrial translocation of DRP1, leading to mitochondrial fission and apoptosis. Knockdown of PINK1 evidently suppressed mitophagy stimulated by polyphyl lin I, and markedly enhanced DRP1-dependent mitochondrial fission and apoptosis induced by polyphyl in I.Furthermore, suppression of DRP1 by mdivi-1 or sh RNA inhibits PINK1 knockdown-mediated mitochondrial fragmentation and apoptosis in response to polyphyllin treatment, suggesting that the depletion of PINK1 lead to mitochondrial fragmentation due to excessive fission. Our in vivo study also showed that knockdown of PINK1potentiated polyphyllin I-mediated inhibition of tumor growth in a breast cancer cell xenograft mouse model. CONCLUSION Our study provides a mechanism to support the role of PINK1 in the regulation of polyphyl in I-induced mitophagy and apoptosis, and suggest polyphylin Ias a potential drug for treatment of breast cancer.