Bcl-2 and caspase-3 are major regulators in Agaricus blazei-induced human leukemic U937 cell apoptosis through dephoshorylation of Akt

Biol Pharm Bull. 2007 Aug;30(8):1432-7. doi: 10.1248/bpb.30.1432.


Agaricus blazei is a medicinal mushroom that possesses antimetastatic, antitumor, antimutagenic, and immunostimulating effects. However, the molecular mechanisms involved in A. blazei-mediated apoptosis remain unclear. In the present study, to elucidate the role of the Bcl-2 in A. blazei-mediated apoptosis, U937 cells were transfected with either empty vector (U937/vec) or vector containing cDNA encoding full-length Bcl-2 (U937/Bcl-2). As compared with U937/vec, U937/Bcl-2 cells exhibited a 4-fold greater expression of Bcl-2. Treatment of U937/vec with 1.0-4.0 mg/ml of A. blazei extract (ABE) for 24 h resulted in a significant induction of morphologic features indicative of apoptosis. In contrast, U937/Bcl-2 exposed to the same ABE treatment only exhibited a slight induction of apoptotic features. ABE-induced apoptosis was accompanied by downregulation of antiapoptotic proteins such as X-linked inhibitor of apoptosis protein (XIAP), inhibitor of apoptosis protein (cIAP)-2 and Bcl-2, activation of caspase-3, and cleavage of poly(ADP-ribose)polymerase (PARP). Ectopic expression of Bcl-2 was associated with significantly induced expression of antiapoptotic proteins, such as cIAP-2 and Bcl-2, but not XIAP. Ectopic expression of Bcl-2 also reduced caspase-3 activation and PARP cleavage in ABE treated U937 cells. Furthermore, treatment with the caspase-3 inhibitor z-DEVD-fmk was sufficient to restore cell viability following ABE treatment. This increase in viability was ascribed to downregulation of caspase-3 and blockage of PARP and PLC-gamma cleavage. ABE also triggered the downregulation of Akt, and combined treatment with LY294002 (an inhibitor of Akt) significantly decreased cell viability. The results indicated that major regulators of ABE-induced apoptosis in human leukemic U937 cells are Bcl-2 and caspase-3, which are associated with dephosphorylation of the Akt signal pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agaricus / chemistry*
  • Apoptosis / drug effects*
  • Caspase 3 / metabolism
  • Caspase 3 / physiology*
  • Caspase Inhibitors
  • Caspases / metabolism
  • Cell Survival / drug effects
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme Activation / drug effects
  • Flow Cytometry
  • Fluorescent Dyes
  • Humans
  • Indicators and Reagents
  • Indoles
  • Oligopeptides / pharmacology
  • Oncogene Protein v-akt / metabolism
  • Oncogene Protein v-akt / physiology*
  • Phosphorylation
  • Proto-Oncogene Proteins c-bcl-2 / physiology*
  • U937 Cells


  • Caspase Inhibitors
  • Fluorescent Dyes
  • Indicators and Reagents
  • Indoles
  • Oligopeptides
  • Proto-Oncogene Proteins c-bcl-2
  • benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone
  • DAPI
  • Oncogene Protein v-akt
  • Caspase 3
  • Caspases