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Oncol Rep. 2014 Apr;31(4):1653-60. doi: 10.3892/or.2014.3008. Epub 2014 Jan 31.

Momilactone B induces apoptosis and G1 arrest of the cell cycle in human monocytic leukemia U937 cells through downregulation of pRB phosphorylation and induction of the cyclin-dependent kinase inhibitor p21Waf1/Cip1.

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  • 1Department of Molecular Biology, College of Natural Sciences, Dongeui University, Busan 614-714, Republic of Korea.
  • 2Department of Anatomy and Cell Biology, Dong-A University College of Medicine and Mitochondria Hub Regulation Center, Busan 602-714, Republic of Korea.
  • 3Laboratory of Immunobiology, Department of Marine Life Sciences, Jeju National University, Jeju 690-756, Republic of Korea.
  • 4Department of Biochemistry, Dongeui University College of Oriental Medicine, Busan 614-052, Republic of Korea.
  • 5Department of Applied Life Science, College of Life and Environmental Science, Konkuk University, Seoul 143-701, Republic of Korea.
  • 6Department of Urology, Chungbuk National University College of Medicine, Cheongju 361-763, Republic of Korea.


Momilactone B, a terpenoid phytoalexin present in rice bran, has been shown to exhibit several biological activities. The present study was conducted using cultured human leukemia U937 cells to elucidate the possible mechanisms by which momilactone B exerts its anticancer activity, which to date has remained poorly understood. Momilactone B treatment of U937 cells resulted in a dose-dependent inhibition of cell growth and induced apoptotic cell death as detected by chromatin condensation, DNA fragmentation, the cleavage of poly(ADP-ribose) polymerase and Annexin V-FITC staining. Flow cytometric analysis revealed that momilactone B resulted in G1 arrest in cell cycle progression, which was associated with the dephosphorylation of retinoblastoma protein (pRB) and enhanced binding of pRB with the E2F transcription factor family proteins. Treatment with momilactone B also increased the expression of cyclin-dependent kinase (Cdk) inhibitor p21Waf1/Cip1 in a p53-independent manner, without any noticeable changes in G1 cyclins and cyclin-dependent kinases (Cdks), except a slight decrease in cyclin E. Moreover, in vitro kinase assay indicated that momilactone B significantly decreased Cdk4- and Cdk6-associated kinase activities through a notably increased binding of p21 to Cdk4 and Cdk6. Our results demonstrated that momilactone B caused G1 cell cycle arrest and apoptosis in U937 cells through the induction of p21 expression, inhibition of Cdk/cyclin-associated kinase activities, and reduced phosphorylation of pRB, which may be related to anticancer activity.

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