1. Regulator of the apoptotic pathway
BCL-2
Regulator of the apoptotic pathway
Heather Anderson

2. Discovery of first antiapoptotic gene
Tsujimoto, Cossman, Jaffe, and Croce first cloned portions of the Bcl-2 gene in 1985
Discovery of antiapoptotic activity and oncogenic potential of Bcl-2 by Vaux and Cory Adams in 1988
In 1989 experiments with transgenic mice showed that overexpression of Bcl-2 causes accumulation of B lymphocytes
Later Vaux, Weissman, and Kim showed that Bcl-2 controlled an evolutionary conserved pathway

3. What is apoptosis? Process of programmed cell death Necrosis
Morphological changes
Necrosis
Acute cellular injury
Essential for defense against virus, development, and tissue homeostasis (

4. Structure of Bcl-2 Contains 4 BH domains
Located on the endoplasmic reticulum membrane, nuclear envelope, and outer membrane of the mitochondria
Hydrophobic C terminal domain places it on the cytoplasmic face of the mitochondrial outer membrane
BH3
BH4
Figure 3: Nature Reviews/ Cancer Volume 2
(© 2002 Nature Publishing Group)

5. Normal Apoptosis: mitochondrial pathway
Bcl-2 inhibits apoptosis
Upon cellular damage Bax/Bak migrates to mitochondria, inhibits Bcl-2, and form pores in the outer membrane
Cytochrome c leaks out of the mitochondria and binds to Apaf-1 (apoptotic protease activating factor-1)
Use ATP to form apoptosomes ad activate caspase-9
Caspase-9 cleaves caspase-3 and caspase-7 (

6. Stress pathway to apoptosis
Bcl-2 pathway
C. Elegan pathway
Initiation of apoptosis also requires BH3 proteins
Detect developmental death signals or intracellular damage
Bind in groove on Bcl-2 and lead to heterodimerization
Activation of apoptosis requires only one BH3 protein (EGL-1)
Ced-9 directly binds to and inhibits Ced-4
EGL-1 displaces Ced-4 which then activates the Ced-3 caspase leading to apoptosis

7. Functions of Bcl-2 in the cell
Prevents apoptosis and necrosis
Controls homeostasis
Maintains membrane integrity on mitochondria
Inhibits Bax conformational change
May also gate mitochondrial pore or compete for Bax target
Required for survival of kidney, melanocyte stem cells, and mature lymphocytes

8. B-cell lymphoma B cell mutates and becomes cancerous Symptoms:
Swollen lymph nodes, night sweats, tired, weight loss, and high temperatures
Most common is follicular lymphoma
Cleaved or non- cleaved cells
Prognosis: median of 10 years ( (

9. Bcl-2 mutations
Bcl-2 is an oncogene, overexpression of this gene prevents apoptosis which leads to cancer
80 to 90% of follicular lymphomas, 30% diffuse large cell lymphomas
Also found in chronic lymphocytic leukemia, acute lymphoblastic leukemia, acute promyelocytic leukemia, Burkitt lymphoma, and diffuse large B-cell lymphoma
Transgenic mouse models

10. Bcl-2 mutation in B-cell lymphoma
Bcl-2 is located on chromosome 18
Reciprocal translocation of chromosome 18 and 14 leads to overexpression of Bcl-2
Chromosome 14 contains the heavy antibody chain
Cell death is delayed leading to cell proliferation
Prevent activation of caspases (

11. Summary Bcl-2 inhibits apoptosis in the mitochondrial pathway
Bcl-2 pathway is important in maintaining mitochondrial integrity and cell homeostasis especially with B-cells
Translocation of chromosome 14 and 18 places Bcl-2 gene next to the antibody heavy chain enhancer
High levels of Bcl-2 protect B-cells from early cell death, leading to B-cell lymphoma