Early events in Bcl-2-enhanced apoptosis

Apoptosis. 2003 Dec;8(6):609-16. doi: 10.1023/A:1026135509274.


Transfection of PC12 pheochromocytoma cells with bcl-2 potentiates apoptosis induced by the antimitotic agent, neocarzinostatin (NCS). The mechanism of potentiation involves caspase 3-dependent cleavage of Bcl-2 to its pro-apoptotic counterpart, but the cellular events proximal to caspase 3 activation in this system are not known. Two min after initiation of NCS treatment, Bax begins to translocate from cytosol to the mitochondria; the mitochondrial localization of Bax persists for 30 min after NCS treatment. At the same time, cytochrome C is released from the mitochondria to cytosol. The mitochondrial membrane potential exhibits differential change in mock- and bcl-2 -transfected PC12 cells. In mock-transfected PC12 cells, the mitochondrial membrane potential increases immediately, peaks at 15 min following initiation of NCS treatment, and drops thereafter. In contrast, in bcl-2 -transfected PC12 cells, the membrane potential drops immediately following NCS treatment. Caspase 9 is activated and peaks at 10 min in both mock- and bcl-2 transfected PC12 cells, however, the peak activity of caspase 9 is higher and caspase 9 activation lasts longer (30 min) after the treatment in bcl-2 transfectants. Not until 30 min after initiation of a 1 h treatment with NCS is Bcl-2 protein cleaved in bcl-2 -transfected cells. Thus, in bcl-2 -transfected cells, the mitochondrial membrane potential drops and cytochrome C is released from the mitochondria despite the presence of large amounts of intact mitochondrial Bcl-2. This makes it unlikely that cleavage of Bcl-2 is the only factor involved in potentiation of NCS-induced apoptosis by Bcl-2.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antibiotics, Antineoplastic / pharmacology
  • Apoptosis / physiology*
  • Caspase 9
  • Caspases / drug effects
  • Caspases / metabolism
  • Cytochromes c / metabolism
  • Cytosol / drug effects
  • Cytosol / metabolism
  • Mitochondria / drug effects
  • Mitochondria / metabolism
  • PC12 Cells
  • Protein Transport / drug effects
  • Protein Transport / physiology
  • Proto-Oncogene Proteins / drug effects
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-bcl-2 / physiology*
  • Rats
  • Zinostatin / pharmacology
  • bcl-2-Associated X Protein


  • Antibiotics, Antineoplastic
  • Bax protein, rat
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-2-Associated X Protein
  • Cytochromes c
  • Zinostatin
  • Casp9 protein, rat
  • Caspase 9
  • Caspases