Natural Lignan Justicidin A‐Enhanced Mitophagy and Mitogenesis in Cytotoxicity of Grade III Human Bladder Cancer Cells

Mitochondria are crucial organelles for energy metabolism, cell signaling, and apoptosis in mammalian cells. To maintain cellular homeostasis, the cell has evolved complex systems for the quality control of mitochondria. Justicidin A (JA) is a novel and structure‐defined arylnaphthalide lignan isolated from Justicia procumbens , which has been used as an herbal remedy in Taiwan and China for fever, cancer, and pain. Our previous reports show that JA suppressed the growth of human hepatocellular carcinoma Hep 3B and human colorectal cancer HT‐29 cells in NOD‐SCID mice, and the JA‐induced cytotoxicity was observed via induction of autophagy and mitochondrion‐related apoptosis. JA also preferentially inhibited the population growth of many other cancer cell types including grade III human bladder cancer T24 cells, compared to that of normal human peripheral blood mononuclear cells (PBMC). The 50% population growth inhibition of JA for PBMC was at least 1000‐fold higher than that for T24 cells. In the present study, we reveal that JA‐induced autophagy in T24 cells, characterized by increases in LC3‐II expression and acidic vesicular organelles formation, was paralleled by inhibition of mTOR, production of Atg5‐Atg12 complex, and activation of MEK/ERK. The JA‐triggered alternation of mitochondrial membrane potential, determined by staining with rhodamin123 followed by flow cytometry, in combined with the occurrence of autophagy implies the degradation of damaged mitochondria by a form of selective autophagy (mitophagy). Elevation of phospho‐Parkin and BNIP3 expressions by Western and co‐localization of BNIP3 and LC3 puncta by confocal microscopy indicate that the JA‐induced mitophagy proceeded via the Parkin‐ and BNIP3‐related pathways. Since mitophagy is balanced by mitochondrial biogenesis for generation of new mitochondria (mitogenesis), the increase in the intensity of Mito‐Tracker deep red and nonyl acridine orange as well as upregulation of mitochondrial UQCRC1 and COXIV protein expressions reveal the induction of mitogenesis in JA‐treated cells. Nevertheless, co‐administration of JA enhanced cytotoxicity of T24 cells to a combination of cisplatin and gemcitabine, the standard first‐line treatment for patients with locally advanced and metastatic bladder cancer, and produced a synergistic effect. Overall, our data indicate a possible role of mitophagy and mitogenesis in JA‐induced cytotoxicity of bladder cancer cells. Support or Funding Information Supported in part by the Ministry of Science and Technology, Taiwan, No. MOST 105‐2320‐B‐003‐003 and 106‐2320‐B‐003‐006‐MY3 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .