The Role of Bcl-2 in Apoptosis and Cancer Eddie Alcorn

Bcl-2 aids in preventing apoptosis. Hanahan and Weinberg, Cell 100:57-70 (2000)

Table of Contents The cell machinery and jobs of Bcl-2 in a typical cell How the absence of Bcl-2 impacts an organism during development The effect of Bcl-2 on tumorigenesis

Bcl2 is part of a family of related proteins that play different roles in apoptosis. Cory, S., Adams, J.M. Nature 2, (2002)

Most cellular Bcl-2 is bound to the outer mitochondrial membrane. Cory, S., Adams, J.M. Nature 2, (2002)

At the membrane, Bcl-2 blocks Bax and Bak activity. Cory, S., Adams, J.M. Nature 2, (2002)

BH3-only protein binds and inhibits Bcl-2, discontinuing its obstruction to Bax and Bak activity. Cory, S., Adams, J.M. Nature 2, (2002)

Bax and Bak release Cytochrome C and Diablo from the mitochondria to induce apoptosis. Cory, S., Adams, J.M. Nature 2, (2002)

Table of Contents The cell machinery and jobs of Bcl-2 in a typical cell How the absence of Bcl-2 impacts an organism during development The effect of Bcl-2 on tumorigenesis

In a Bcl-2 knockout mouse, neonatal kidney and immune system are destroyed by cell suicide. Melanocytes are driven to enter apoptosis, eventually yielding grey mice. Kamada, S et al. Figure 2A

Experiments have shown that a Bcl-2 knockout mouse can be rescued by loss of a single allele in a BH3-only protein. Cory, S., Adams, J.M. Nature 2, (2002) BH3-only +/+ and Bcl2 -/- => Apoptosis BH3-only +/- and Bcl2 -/- => Rescue

Table of Contents The cell machinery and jobs of Bcl-2 in a typical cell How the absence of Bcl-2 impacts an organism during development The effect of Bcl-2 on tumorigenesis

Chromosomal translocation of the Bcl-2 causes B-cell lymphoma.

Bcl-2 becomes linked an active immunoglobulin promoter, stimulating its overexpression in B-lymphoid tumors. Duronio, R. Feb. 20, 2007

Transgenic mice with the Bcl-2 transgene, Myc transgene, and a combination of both demonstrated their respective roles in cancer initiation. Weinberg, R.A. Figure 9.22A

Excess Myc and Bcl-2 combined caused mutant mice to die from lymphomas at a high rate. Weinberg, R.A. Figure 9.22B

Summary of Bcl-2 Properties 1. Inhibits apoptosis and associates with outer mitochondrial membrane. 2. Internal organs of Bcl-2 knockout mice are ravaged by apoptosis. 3. Bcl-2 is overexpressed in B-cell lymphomas by chromosomal translocation

References Cory, S., Adams, J.M. The Bcl-2 Family: Regulators of the Cellular Life-or-Death Switch. Nature 2, (2002) Kamada, S. et al. Bcl-2 deficiency in mice leads to pleiotropic abnormalities: accelerated lymphoid cell death in thymus and spleen, polycystic kidney, hair hypopigmentation, and distorted small intestine. Cancer Research 55, (1995) Veis DJ, Sorenson CM, Shutter JR, Korsmeyer SJ. Bcl-2- deficient mice demonstrate fulminant lymphoid apoptosis, polycystic kidneys, and hypopigmented hair. Cell 75, (1993) Weinberg, Robert A. The Biology of Cancer. New York: Garland Science, Weissman, D. “Pathology Lectures and Case Conferences.” Jul UMDNJ - Robert Wood Johnson Medical School. 25 Feb

Class Handout The Role of Bcl-2 in Apoptosis and Cancer 1. Bcl-2 is pro-survival protein that hinders a cell’s entry into apoptosis. -Bcl-2 homology (BH) domains show the similarities between Bcl-2, BH3-only, and Bax proteins. -Similar regions explain binding affinity and localization inside the cell. -Located on the outer mitochondrial membrane and prevents activation of Bak and Bax. -BH3-only proteins serve to block the function of Bcl-2 and promote entry into apoptosis. 2. Knockout mice further demonstrate the link between Bcl-2 and apoptosis. -Bcl-2 mutants undergo massive apoptosis inside certain organs and do not properly execute melanin synthesis (gray mice). -If even one allele of a primary BH3-only protein is lost as well, the Bcl-2 mutant mouse is rescued. 3. When Bcl-2 is linked to an immunoglobulin locus via chromosomal translocation, it becomes hyperactive and can produce B-cell lymphomas. -By ignoring cellular damage and cytotoxic signals, these cancerous B-cells develop into tumors. -Surplus Bcl-2 combined with an excess of Myc, a promoter of proliferation, causes mice to die at a higher rate than overexpression of either gene.