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Stem Cell Theory of Carcinogenesis-Classical and

Most Recent Evidence

Stem Cell Theory of Carcinogenesis-Classical and

Most Recent Evidence

Chia-Cheng Chang, Ph.D.

Dept. Pediatrics and Human Development Michigan State University

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The Origin of Undifferentiated State of Tumor Cells

The re la t ively undif ferent ia ted s ta te of certain tumor cells is reminiscent of the stateof embryonic cells prior to theirspecialization during development.

Gene and the Biology of CancerHarold Varmus and Robert A. Weinberg

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1.Dedifferentiation2.Blocked differentiation of stem cells

The Origin of Undifferentiated State of Tumor Cells

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◇ Cancer is :

◇ a disease of cell differentiation(Markert, 1968).

◇ oncogeny as blocked or partially blockedontogeny (Potter, 1978).

◇ a disease of the pluripotent stem cell(Sawyers et al., 1991).

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Chronic Myelogenous Leukemia (CML)

◇ t(9:22) Philadelphia chromosome

◇ hybrid mRNA and protein with tyrosinekinase activity (bcr-abl, p210)

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CML is a disease of the pluripotent stem cell

The Philadelphia chromosome is found in all hematopoietic lineages in patients with this malignancy, but not in skin fibroblasts or bone marrow stromal cells.

Sawyers et al.Cell 64:337-350, 1991

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Acute Myeloid Leukaemia (AML)•The most frequent chromosomal abnormalities in

AML involve the 8; 21 translocation, which results in AML1-ETO chimaeric transcripts in leukaemiacells.

•In patients in remission, the AML1-ETO transcripts were found in a fraction of normal HSCs in the marrow, indicating that the translocation occurred originally in normal HSC and that additional mutations subsequently lead to leukaemia.(CD34＋ Cd38－ Thy-1＋ → CD34＋ Cd38－ Thy-1－)Miyamoto, T et al, Proc . Natl. Acad. Sci. USA 97: 7521-7526, 2000.

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B-Cell Non-Hodgkin’s Lymphoma

“ t (14:18) translocation in all hematopoietic cell lineage”

S. Yarkoni et al.(J. Nat. Cancer Inst., 88: 973-9, 1996)

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Cancer Instances in Large and Small Intestines

◇ Small Intestines 350 new cases/year◇ Large Intestines 28,600 new cases/year

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The Role of Bcl-2 in Maintaining Stem Cell Integrity

The anti-apoptotic gene bcl-2 is expressed at the base of murine and human colonic crypts, whereas expression is not seen in the small intestine, supporting the view that bcl-2 increases the apoptotic threshold of colonic stem cells.

Merritt et al., J. Cell Sci. 108:2261-2271, 1995

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Location of apoptotic cells following cytotoxic exposure

Small intestine---At stem cell positionHigh frequency (altruistic suicide)

Large intestine---Not limited to stem cell positionLow frequency

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Pregnancy and Reduced Risk of Breast Cancer

1. Decreased stem cell multiplication (John Cairns,1975)

2. Induced differentiation of mammary gland (L.H. Russo et al., 1990)

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Lobule 1 Lobule 2 Lobule 3

Three Lobule Types of Breast Tissue

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Terminal End Buds of Mammary Gland as Major Target for Carcinogenesis

Carcinogen acts on the TEB and that this structure is the one that evolves to intraductal proliferation, carcinoma in situ, and invasive carcinoma.

I.H. Russo and J. RussoEnviron. Health Perspectives 104:938-967, 1996

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High susceptibility of a human breast epithelial cell type with stem

cell characteristics to telomerase activation and immortalization

W. Sun, K.S. Kang, I. Morita, J.E. Trosko and C.C. Chang Cancer Res. 59 : 6118-6123, 1999.

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Function of SV40 Large T-antigen

1.Inactivating p53 and pRb.

2.Inducing a CCAAT box binding factor which transactivates cyclin A, cdc2, DNA polymerase α, thymidine kinase etc.

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Major Events in Carcinogenesis

(1) Altered cell cycle regulation – bypassing cellular senescence. → (2) Telomerase activation – immortalization → (3) Activation of a growth-promoting pathway – tumorigenic → (4) Altered cell adhesion, mobility and protease/collagenase activity –invasion and metastasis.

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A Nucleolar mechanism controlling cell proliferation in stem cells and cancer cells.

R.Y.L. Tsai and R. D.G. McKay

Genes and Development 16: 2991-3003, 2002.

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Nucleostemin

A novel protein containing an N-terminal basic domain and two GTP-binding domain.Function : regulate cell proliferation, differentiation, apoptosis in a p53-dependent manner.Found in the nucleoli of CNS stem cells, embryonic stem cells and several cancer cell lines. When stem cells differentiate, nucleostemin expression decreases rapidly.

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Gap Junctional Intercellular Communication of HL1-1 Cell Line

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GJIC in L1SV1 Cells

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GJIC in Heptoma Cells

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Current Opinion in Cell Biology 1998; 10:710

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Vimentin and α-foetoproteinare collectively termed the“oval cell phenotype”

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Expression of Vimentin in HL1-1 Cell Line

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Expression of Vimentin in L1SV1 Cells

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Expression of Alpha Foetoprotein in HL1-1 Cell Line

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Expression of Alpha Foetoprotein in L1SV1 Cells

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Anchorage Independent Growth of HL1-1 Cell Line

AIG = 4.6% Colony forming efficiency on plastic = 11%

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Similarity Between Putative Human Liver Stem Cells and

Hepatocellular Carcinoma

Deficient in gap junctional intercellular communicatioonExpression of VimentinExpression alpha foetoproteinAbility of anchorage independent growth

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1.Deficient in gap junctional intercellular communication.

2.Ability of anchorage independent growth.3.Similar phenotypes of human breast

epithelial stem cells and breast cancer cells CX26－, α-6 integrin－, maspin－, estrogen receptor (ER＋).

Similarity of Stem Cells and Tumor Cells

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Similarity of Stem Cells and Tumor Cells

4.Nucleostemin, a novel protein found in thenucleoli of CNS stem cells, embryonic stemcells and several cancer cell lines.When stem cells differentiate, nucleosteminexpression decrease rapidly prior to cell-cycle exit both in vitro and in vivo.

5.Expression of alpha foetoprotein and vimetin in liver stem cells and liver tumor cells

6..Contact-insensitive growth (e.g. kidney epithelial stem cells)

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These results are consistent with “Oncogeny as blocked or partially

blocked ontogeny” theory -------by Van R. Potter

and The stem cell theory of carcinogenesis

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Paradoxical effects of phenobarbital on mouse

hepatocarcinogenesis

G.H. LeeToxicologic Pathology 28 :

215-225, 2000

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Protocol One--Postweaning

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Protocol Two--Postweaning

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Protocol Three--Preweaning

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Discussion

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Discussion

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Why Stem Cells Are Key Target Cells for Carcinogenesis

1.Stem cells express many tumor cell phenotypes, fewer mutations or epigenetic alterations may be required for tumor progression. 〔Human embryonic stem cells are immortal and tumorigenic (teratoma)〕

2.Stem cells have unlimited or extended lifespan, there is a much greater opportunity for mutations to accumulate.•Human breast epithelial stem cells are more

susceptible to telomerase activation andimmortalization.

•Stem cells of large intestine have higher thresholdfor apoptosis ( bcl-2 expression).

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Two Types of Target Cells for Carcinogenesis

Liver : Basophilic tumors – inhibition by phenobarbitalEosinophilic tumors – promotion byphenobarbital

Breast : Hormone dependent (ER＋) – Vimentin＋

Cytokeratin 19－

Hormone independent (ER－) – Vimentin－(50%)Cytokeratin 19＋(50%)

Prostate : Androgen dependentAndrogen independent

Skin : Basal cell carcinomaSquamous cell carcinoma

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Acknowledgement of Co-Workers

Chien-Yuan Kao Koichiro NomataIkue Morita Angela CruzChing-Yi Hsieh Wei SunMaki Saitoh James E. TroskoJin Lian Tsai