Investigation of the subcellular distribution of the bcl-2 oncoprotein: residence in the nuclear envelope, endoplasmic reticulum, and outer mitochondrial membranes

Cancer Res. 1993 Oct 1;53(19):4701-14.


A multidisciplinary approach was taken to investigate the intracellular locations of the 26-kDa integral membrane protein encoded by the bcl-2 gene. Subcellular fractionation analysis of a t(14;18)-containing lymphoma cell line revealed the presence of Bcl-2 protein in nuclear, heavy-membrane, and light-membrane fractions but not in cytosol. Sedimentation of heavy-membrane fractions in Nycodenz and Percoll continuous gradients demonstrated comigration of p26-Bcl-2 with mitochondrial but not other organelle-associated proteins. Fractionation of light-membrane fractions using discontinuous sucrose-gradients revealed association of Bcl-2 protein primarily with lighter-density microsomes (smooth endoplasmic reticulum) as opposed to heavy-density microsomes (rough endoplasmic reticulum). Immune microscopy studies using laser-scanning microscopy, pre- and postembedding electron microscopic methods, and six different anti-Bcl-2 antibodies demonstrated Bcl-2 immunoreactivity in the nuclear envelope and outer mitochondrial membrane in a patchy distribution. Furthermore, anti-Bcl-2 antibody immunoreactivity generally appeared to directly overlie the nuclear envelope in high magnification electron microscopic studies, reminiscent of nuclear pore complexes. Addition of in vitro translated p26-Bcl-2 to isolated translocation-competent mitochondria revealed transmembrane domain-dependent association of Bcl-2 protein with mitochondria but provided no evidence for import into a protease-resistant compartment, consistent with immunomicroscopic localization to the outer mitochondrial membrane. Taken together, the findings demonstrate that p26-Bcl-2 resides primarily in the nuclear envelope, endoplasmic reticulum, and outer mitochondrial membrane in a nonuniform distribution suggestive of participation in protein complexes perhaps involved in some aspect of transport.

Publication types

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

MeSH terms

  • Cell Fractionation / methods
  • Centrifugation, Density Gradient
  • Endoplasmic Reticulum / metabolism*
  • Endoplasmic Reticulum / ultrastructure
  • Humans
  • Lymphoma, B-Cell
  • Mitochondria / metabolism*
  • Mitochondria / ultrastructure
  • Nuclear Envelope / metabolism*
  • Nuclear Envelope / ultrastructure
  • Organelles / metabolism*
  • Organelles / ultrastructure
  • Protein Biosynthesis
  • Protein-Tyrosine Kinases / analysis
  • Protein-Tyrosine Kinases / metabolism
  • Proto-Oncogene Proteins / analysis
  • Proto-Oncogene Proteins / biosynthesis
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-bcl-2
  • Proto-Oncogenes*
  • Submitochondrial Particles / metabolism
  • Submitochondrial Particles / ultrastructure
  • Transcription, Genetic
  • Tumor Cells, Cultured


  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Protein-Tyrosine Kinases