The Story of Bcl-2 Linking cell apoptosis to tumor metastasis Crystal structure of Bcl-2 complex By Yaming Wang

History Bcl-2 was first isolated in B Cell Lymphoma cells Bcl-2 was first isolated in B Cell Lymphoma cells Caused by malignant B lymphocytes Caused by malignant B lymphocytes Contributes about 85% of known types of lymphoma in US Contributes about 85% of known types of lymphoma in US Immunofluorescence stain of B cells in the spleen (green= Bcl-2)

History continued The mutation of Bcl-2 was due to chromosome translocation The mutation of Bcl-2 was due to chromosome translocation Very similar to the story of Cyclin D as an oncogene Very similar to the story of Cyclin D as an oncogene

Mistake happens during BCR (VDJ) rearrangement Bcl-2 gene (from chromosome 14) is placed next to Ig heavy chain locus on chromosome 18 Bcl-2 gene (from chromosome 14) is placed next to Ig heavy chain locus on chromosome 18 This leads to the overexpression of Bcl- 2 in B cells This leads to the overexpression of Bcl- 2 in B cells

But what is the mechanism that makes Bcl-2 a killer? Bcl family proteins govern programmed cell death (apoptosis)

Bcl-2 protein Biochemistry Bcl-2 is a small protein (~29KD) Bcl-2 is a small protein (~29KD) Bcl family proteins play crucial role in cell apoptosis Bcl family proteins play crucial role in cell apoptosis Divided into pro-survival and pro-apoptosis and usually balance each other out in healthy cells Divided into pro-survival and pro-apoptosis and usually balance each other out in healthy cells Bcl-2 is a pro-survival protein and it protects cell from a wide range of cytotoxic insults, including cytokine deprivation, UV and  -irradiation Bcl-2 is a pro-survival protein and it protects cell from a wide range of cytotoxic insults, including cytokine deprivation, UV and  -irradiation

Highly conserved BH domains Bcl family proteins share highly conserved regions called Bcl homology (BH) domain Bcl family proteins share highly conserved regions called Bcl homology (BH) domain Structurally, divided into 3 families Structurally, divided into 3 families BH3-only family proteins bind to pro-survival family proteins at the groove formed by BH1, BH2, and BH3 domains BH3-only family proteins bind to pro-survival family proteins at the groove formed by BH1, BH2, and BH3 domains Binding triggers the switch of apoptosis signaling Binding triggers the switch of apoptosis signaling

Proposed Mechanism - protection of mitochondrial integrity by Bcl-2

Bcl proteins are highly regulated In response to different signal (ie. Death, or proliferation), Bcl family proteins are up/ down regulated. In response to different signal (ie. Death, or proliferation), Bcl family proteins are up/ down regulated. Example: Regulation of T lymphocytes Example: Regulation of T lymphocytes

Yaming Wang, unpublished data, Microbiology and Immunology, 2006 In response to the immunosuppression signal, Bcl-XL level is down regulated.

What happen if Bcl-2 is over expressed or knocked out in mice?

Bcl-2 over expressing mice: Bcl-2 over expressing mice: B cell lymphomas are frequently found B cell lymphomas are frequently found Bcl-2 knock out mice: Bcl-2 knock out mice: Viable but show growth retardation Viable but show growth retardation Severe polycystic kidney disease Severe polycystic kidney disease Massive apoptotic involution in thymus and spleen Massive apoptotic involution in thymus and spleen

Linking anti-apoptosis to tumor metastasis Bcl-2 is also over expressed in many cancers including lung, colorectal, prostate, and breast, as well as in leukemia and other lymphomas Bcl-2 is also over expressed in many cancers including lung, colorectal, prostate, and breast, as well as in leukemia and other lymphomas

Several changes are required Several changes are required Eg. they have to lose their dependence to local growth factors, ability to survive without integrin signals Eg. they have to lose their dependence to local growth factors, ability to survive without integrin signals All these changes normally lead to cell apoptosis All these changes normally lead to cell apoptosis Overcome by overexpressing pro- survival Bcl family proteins Overcome by overexpressing pro- survival Bcl family proteins Alberts et al. Fig

Recent studies have shown that prolonged cell survival induced by the overexpression of Bcl-2 protein promotes the metastasis of many cancer cells such as melanoma cells and mammary epithelial cells. Recent studies have shown that prolonged cell survival induced by the overexpression of Bcl-2 protein promotes the metastasis of many cancer cells such as melanoma cells and mammary epithelial cells. Therefore, it maks Bcl protein a very good target for cancer therapy. Therefore, it maks Bcl protein a very good target for cancer therapy.

References The lymphoma information network. The lymphoma information network. Veis D.J., Sorenson C.M., Bcl-2-deficient mice demostrate fulminant lymphod apoptosis, polycystic kidneys, and hypopigmented hiar, Cell, 75, 2, Veis D.J., Sorenson C.M., Bcl-2-deficient mice demostrate fulminant lymphod apoptosis, polycystic kidneys, and hypopigmented hiar, Cell, 75, 2, Pinkas J., Martin S.S., Bcl-2-mediated cell survival promotes metastasis of EpH4 BMEKDD mammary epithelial cells, Mol Cancer Res; 2(10), 2004 Pinkas J., Martin S.S., Bcl-2-mediated cell survival promotes metastasis of EpH4 BMEKDD mammary epithelial cells, Mol Cancer Res; 2(10), 2004 Anderson M.H., Svane I.M., Immunogenicity of Bcl-2 in patients with cancer, Blood, 105, 2, 2005 Anderson M.H., Svane I.M., Immunogenicity of Bcl-2 in patients with cancer, Blood, 105, 2, 2005 Takaoka A., Adachi M., Anti-cell death activity protomtes pulmonary metastasis of melanoma cells, Oncogen, 14, 1997, Takaoka A., Adachi M., Anti-cell death activity protomtes pulmonary metastasis of melanoma cells, Oncogen, 14, 1997, Cory S., Adams J.M., The Bcl-2 family: regulators of the cellular life- or-death switch, Nature, 2, 2002, Cory S., Adams J.M., The Bcl-2 family: regulators of the cellular life- or-death switch, Nature, 2, 2002,

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Cancer therapies targeting Bcl-2 over expression Some drugs that inhibit Bcl-2 by BH3 mimetics Some drugs that inhibit Bcl-2 by BH3 mimetics Antisense oligonucleotide (inhibit mRNA translation) Antisense oligonucleotide (inhibit mRNA translation) More interestingly, shown that Bcl-2 over expression is in fact immunogenic. (meaning we can generate immunity against cells in which Bcl-2 is over expressed. ie. cancer cells.) More interestingly, shown that Bcl-2 over expression is in fact immunogenic. (meaning we can generate immunity against cells in which Bcl-2 is over expressed. ie. cancer cells.) This gives us a way to target cancer cells using the weapons in our body (immune system) without harming healthy cells in cancer therapy. This gives us a way to target cancer cells using the weapons in our body (immune system) without harming healthy cells in cancer therapy.