Metarhizin A suppresses cell proliferation by inhibiting cytochrome c oxidase activity.
OBJECTIVE
Metarhizin A was originally isolated from Metarhizium flavoviride as a potent inhibitor of the growth of insect and mammalian cells. In this study, we aimed to understand the molecular targets of metarhizin A involved in its anti-proliferative activity against human cells.


METHODS
Cell cycle regulators and signaling molecules were examined by immunoblotting using specific antibodies. A mitochondria-enriched fraction was prepared from mouse liver, and mitochondrial activity was monitored using an oxygen electrode. Enzyme activity was measured using purified cytochrome c oxidase and permeabilized cells.


RESULTS
Metarhizin A inhibits the growth of MCF-7 cells with an IC50 value of ~0.2 μM and other cells in a similar manner; a cell cycle-dependent kinase inhibitor, p21, is selectively induced. Significant amounts of reactive oxygen species (ROS) are generated and ERK1/2 is activated in cells treated with metarhizin A. Metarhizin A completely suppresses oxygen consumption by mitochondria, and potently inhibits the activity of cytochrome c oxidase. It induces cell death when MCF-7 cells are cultured under limiting conditions.


CONCLUSIONS
Metarhizin A is a potent inhibitor of cytochrome c oxidase and activates the MAPK pathway through the generation of ROS, which induces growth arrest of cells, and, under some conditions, enhances cell death. The cytochrome c oxidase system is a possible molecular target of metarhizin A.
Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8678, Japan.
Yasuhiro
Y
Katou
Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan.
Naoya
N
Endo
Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan.
Toshiyuki
T
Suzuki
Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8678, Japan.
Jiang
J
Yu
Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8678, Japan.
Haruhisa
H
Kikuchi
Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8678, Japan.
Yoshiteru
Y
Oshima
Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan. Electronic address: yoshihom@fmu.ac.jp.
Yoshimi
Y
Homma
D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics; D004224:Diterpenes / Q000494:pharmacology*; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D007783:Lactones / Q000494:pharmacology*; D061986:MCF-7 Cells; D052981:Metarhizium / Q000737:chemistry*; D051379:Mice; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D012333:RNA, Messenger / Q000032:analysis; D017382:Reactive Oxygen Species / Q000378:metabolism; D016196:S Phase
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004224:Diterpenes; D004791:Enzyme Inhibitors; D007783:Lactones; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C000588921:metarhizin A; D003576:Electron Transport Complex IV; D020928:Mitogen-Activated Protein Kinases
Entomopathogenic fungi; Mitochondria; ROS; Toxin