谷報道：據《Cancer Cell》雜志2007年3月13日報道,，Dana-Farber癌癥研究所最新的研究對“腫瘤干細胞”假說提出了質疑，該假說認為,，腫瘤組織內有少量可以自我復制的腫瘤干細胞,，腫瘤干細胞在乳腺癌變過程中和癌癥復發(fā)中起主導作用，清除腫瘤干細胞就可治愈癌癥,。
文章報道,，科學家已經從一個乳腺癌組織標本中分離出兩個遺傳背景不同的細胞群，其中之一就是其他科學家堅信存在的乳腺癌腫瘤干細胞,。文章資深作者Kornelia Polyak 指出,，“如果全部的乳腺癌細胞源自同一個癌干細胞，那么僅需用一種藥就可以治愈該病,。但是根據實驗結果,，我們推測,，乳腺癌細胞是來自一種干細胞樣的祖細胞，是由這類細胞分化為遺傳背景不均一的腫瘤細胞,，因此必須對這兩類細胞都進行治療,。”這兩類細胞（干細胞樣祖細胞和癌細胞），或許還有其它的,，都與乳腺癌的癌變過程有關,。研究者對這兩類細胞進行基因掃描分析后，發(fā)現(xiàn)所謂的“腫瘤干細胞”與正常的干細胞很似,，是由一個激活的分子通路誘導產生的,。乳腺癌患者如果含有大量這種干細胞樣細胞，其癌癥復發(fā)的機率是相當高的,。但像這種情況也有其積極的一面,，因為這種腫瘤干細胞樣細胞存在異常的信號活化通路，如目前已知道的TGF-β1信號轉導通路,，而實驗已發(fā)現(xiàn)可以抑制信號活化通路的藥物,，現(xiàn)在這些藥物正進入臨床試驗階段，哈佛醫(yī)學院Polyak副教授指出,。因此,，臨床上使用這些信號活化通路抑制藥物，再加上其它治療,，估計會改善由這類細胞產生的乳腺癌的預后,。
腫瘤的形成是源于細胞的克隆演變還是腫瘤干細胞分化？細胞克隆演變是一個解釋腫瘤形成的理論模型,，該模型認為腫瘤細胞是經過長期的克隆演變篩選出來的：正常的細胞出現(xiàn)突變,，產生了異常的子代細胞克隆，而各個子代細胞又突變產生更加異常的子代細胞克隆,，如此循環(huán)，最終會產生大量的遺傳背景不均一的細胞克隆,，正常細胞變成了癌細胞,，至此腫瘤就形成了。目前另外還有一個解釋腫瘤形成的理論,，其觀點是單一的某種異常類型的成人干細胞產生并促使了腫瘤的形成,，所以最終形成的腫瘤其細胞的遺傳背景是均一的，乳腺癌的產生就是這樣,。腫瘤干細胞假說認為,，用藥物很難將這些少量的可自我復制的腫瘤干細胞殺滅，也許腫瘤干細胞這種耐藥性可解析為何經過成功治療的乳腺癌患者仍會經常復發(fā),。2003年科學家已從患者腫瘤組織里分離出所謂的乳腺癌腫瘤干細胞,，其細胞表面分子CD44認為是腫瘤干細胞特異性分子,，但CD44分子也是正常乳腺細胞的分子標志。CD44陽性細胞輸入給免疫缺陷的小鼠后可形成乳腺腫瘤,?？茖W家還發(fā)現(xiàn)與之緊密相關的細胞為CD22陽性，懷疑其是CD44陽性細胞產生的子代細胞,。
Polyak和Michail Shipitsin領導的研究小組采用基因掃描技術分析這兩類細胞的關系,。他們分別從正常乳腺上皮、胸腔積液,、乳腺癌原位癌患者標本中分離出CD24陽性和 CD44陽性細胞,，再制備成各自的基因文庫進行基因掃描。最后的實驗結果與細胞克隆演化模型理論更相符合,，也就是說,，CD24陽性細胞和 CD44陽性細胞在遺傳背景上并非等同，僅是相似而已,，但按腫瘤干細胞假說的觀點,，CD44陽性細胞為腫瘤干細胞，CD24陽性細胞是其子代細胞,，那么兩者在遺傳背景應該是一致的,。“盡管CD44陽性細胞可表達多種干細胞分子標志，但是,，由同一腫瘤組織分離得到的CD24陽性和 CD44陽性細胞兩者在遺傳背景上是有差異的,，這一結果對腫瘤干細胞假說構成了質疑，同時支持細胞克隆演化模型,，因為該理論可以很好地解釋腫瘤異質性這一現(xiàn)象,。”作者在論文中寫道。
Polyak研究小組進一步發(fā)現(xiàn),，活化的TGF-β1信號轉導通路可誘導CD44陽性細胞產生,，而CD24陽性細胞則沒有這種現(xiàn)象，為此,，他們說,，“臨床上，腫瘤細胞表達CD44分子的較表達CD24的預后更差,，但是,，CD44陽性細胞反而可以提供TGF-β1信號轉導通路為靶點進行治療。”
Figure 1. Purification and Gene Expression Analysis of Distinct Cell Subpopulations
(A) Schematic outline of purification of the various cells from normal breast tissue and invasive and metastatic breast carcinomas. Cells are captured using the indicated antibody-coupled magnetic beads specific for each cell type. Purification steps marked with rectangles were not always included in the procedure, while myofibroblasts, marked with an asterisk, were only present in invasive tumors. IDC, invasive ductal carcinoma. Semiquantitative RT-PCR analysis of purified cell fractions isolated from normal breast tissue (N1) (B), pleural effusion (PE2) (C), and primary invasive ductal carcinoma (IDC28) (D). RNA from CD24+, CD44+, and PROCR+ cells was tested for the expression of known differentiated (Diff) and stem (Stem)-cell-specific genes. CD44+ and PROCR+ cells lack differentiation markers and are positive for stem-cell markers. In the primary invasive tumor, the CD44+ fraction is contaminated by leukocytes, as demonstrated by high levels of CD45 leukocyte common antigen (PTPRC) expression. ACTB was used as loading control. Each triangle indicates an increasing number of PCR cycles (25, 30, 35). (E) Dendrogram depicting relatedness of SAGE libraries prepared from CD44+, PROCR+, and CD24+ cells. Hierarchical clustering was applied to SAGE data for the indicated libraries, and selected portions of the clustering heat map are shown here. Each row represents a tag and is labeled with the symbol of the gene that best matches that tag (or “no match” if no matching transcript was found). Red and green indicate high and low expression levels, respectively. The expression profiles of normal and cancer CD44+ and PROCR+ cells are more similar to each other than to those of CD24+ cells derived from the same tissues. ASC, ascites; PE, pleural effusion; N, normal; IDC, invasive ductal carcinoma. (F) Gene ontology biological process categories highly represented in pools of all SAGE libraries from different cell populations. Categories with an enrichment score >2 in at least one library pool using the DAVID Functional Annotation Tool are plotted. Cell populations represented include cancer CD44+ and PROCR+ (red), normal CD44+ and PROCR+ (pink), cancer CD24+ (dark blue), and normal CD24+ (light blue) cells.
原文出處：
Volume 11, Issue 3, Pages 209-302 (13 March 2007)
Molecular Definition of Breast Tumor Heterogeneity • ARTICLE
Pages 259-273
Michail Shipitsin, Lauren L. Campbell, Pedram Argani, Stanislawa Weremowicz, Noga Bloushtain-Qimron, Jun Yao, Tatiana Nikolskaya, Tatiana Serebryiskaya, Rameen Beroukhim, Min Hu, et al.
SummaryPlus | Full Text + Links | PDF (2914 K)
作者簡介：
Kornelia Polyak, MD, PhD
Assistant Professor of Medicine, Harvard Medical School
Department
Medical Oncology/Molecular and Cellular
Area of Research
Molecular Basis of Breast Cancer Initiation and Progression
Research
Breast cancer is a leading cause of cancer-related death in women of the Western world. The Breast Cancer Genetics Laboratory at DFCI is dedicated to the molecular analysis of human breast cancer, which arises as the result of a series of genetic changes. Our goal is to identify differences between normal and cancerous breast tissue, determine the consequences of these differences, and use this information to improve the clinical management of breast cancer patients.
Although increasing evidence suggests that alterations in the tissue microenvironment contribute to tumorigenesis, the molecular basis of these changes is not well understood. We characterized molecular alterations that occur during breast tumor progression using various genomic technologies including serial analysis of gene expression (SAGE) for gene expression profiling, single nucleotide polymorphism (SNP) arrays and comprehensive genomic hybridization (CGH) arrays for analyzing genetic changes, and methylation specific digital karyotyping (MSDK) for characterizing global DNA methylation profiles.
In addition to analyzing tumor cells, we also investigated all cell types that comprise normal breast tissue and in situ and invasive breast carcinomas. Using these approaches, we determined that gene expression and epigenetic changes occur in all cell types during breast tumor progression, while clonally selected genetic alterations are restricted to tumor epithelial cells. Several of the genes aberrantly methylated in breast cancer, including the HIN-1 gene, are candidate diagnostic or prognostic markers.
By comparing the gene expression and genetic profiles of epithelial cells isolated from normal breast tissue and breast carcinomas (both in situ and invasive), we determined that dramatic changes occur in the transition from normal to ductal carcinoma in situ (DCIS), although we were not able to identify distinct molecular signatures for in situ and invasive carcinomas. This finding suggests that the progression of DCIS to invasive cancer may be influenced by nonepithelial cells.
Related to this finding, a significant fraction of abnormally expressed genes encode secreted proteins and receptors implicating a role for abnormal autocrine/paracrine signaling in breast tumorigenesis. To test the hypothesis that cells comprising the tumor microenvironment contribute to tumor progression, we used a xenograft model of human DCIS. We determined that stromal fibroblasts promote tumor growth and the transition from in situ to invasive carcinoma, while normal myoepithelial cells inhibit tumor growth and progression. Based on our findings, we suggest that interactions among epithelial and stromal cells play a role in tumorigenesis and that targeting these interactions may be exploited for cancer therapy and prevention.
Recent Awards
AACR Sidney Kimmel Symposium for Cancer Research Scholar, 2002
V Foundation Scholar Award, 2001
Sidney Kimmel Scholar Award, 1999
Biography
Dr. Polyak received her MD in 1991 from Albert Szent-Gyorgyi Medical University, Szeged, Hungary, and her PhD in 1995 from Cornell University/Memorial Sloan-Kettering Cancer Center. She completed a research fellowship in oncology at the Johns Hopkins Oncology Center, Baltimore, where she analyzed the mechanism of p53-mediated cell death. Joining DFCI in 1998, she is principally involved in basic laboratory research focusing on cancer genetics and the molecular basis of breast cancer.
select Publications
Hu M, Yao J, Cai L, Bachman KE, van den Brûle F, Velculescu V, Polyak K. Distinct epigenetic changes in the stromal cells of breast cancers. Nat Genet 2005;37:899-905.
Krop I, Parker MT, Bloushtain-Qimron N, Porter D, Gelman R, Sasaki H, Maurer M, Terry MB, Parsons R, Polyak K. HIN-1, an inhibitor of cell growth, invasion, and AKT activation. Cancer Res 2005; Iin press.
Peters BA, Diaz L, Polyak K, Meszler L, Romans K, Guinan EC, Antin JH, Myerson D, Hamilton SR, Vogelstein B, Kinzler KW, Lengauer C. Contribution of bone marrow-derived endothelial cells to human tumor vasculature. Nat Med 2005;11:261-2.
Allinen M, Beroukhim R, Cai, L, Brennan C, Lahti-Domenici J, Huang H, Porter D, Hu M, Chin L, Richardson A, Schnitt S, Sellers W, Polyak K. Molecular characterization of the tumor microenvironment in breast cancer. Cancer Cell 2004;6:17-32.
Burstein HJ, Polyak K, Wong JS, Kaelin CM. Ductal carcinoma in situ of the breast. N Engl J Med 2004;350:1430-40.
Krop I, Player A, Tablante A, Taylor-Parker M, Lahti-Domenici J, Fukuoka J, Batra SK, Papadopoulos N, Richards WG, Sugarbaker DJ, Wright RL, Shim J, Stamey TA, Sellers WR, Loda M, Meyerson M, Jen J, Polyak K. Frequent HIN-1 promoter methylation and loss of expression in multiple human tumor types. Mol Cancer Res 2004;2:489-94.
Vali M, Mehrotra J, McVeigh M, Kominsky SL, Fackler MJ, Lahti-Domenici J, Polyak K, Sacchi N, Argani P, Sukumar S. Very high frequency of hypermethylated genes in breast cancer metastasis to the bone, brain, and lung. Clin Cancer Res 2004;10:3104-9.
Krop I, Maguire P, Lahti-Domenici J, Lodeiro G, Richardson A, Johannsdottir HK, Nevanlinna H, Borg A, Gelman R, Barkardottir RB, Lindblom A, Polyak K. Lack of HIN-1 methylation in BRCA1 linked and "BRCA1-like" breast tumors. Cancer Res 2003;63:2024-7.
Porter D, Polyak K. Cancer target discovery using SAGE. Expert Opin Ther Targets 2003;7:759-69.
Porter D, Weremowicz S, Koei Chin, Seth P, Keshaviah A, Lahti-Domenici J, Bae YK, Monitto CL, Merlos-Suarez A, Chan J, Hulette CM, Richardson A, Morton CC, Marks J, Duyao M, Hruban R, Gabrielson E, Gelman R, Polyak K. A neural growth factor is a candidate oncogene in breast cancer. Proc Natl Acad Sci U S A 2003;100:10931-6.
Instructors
Ian E. Krop, MD, PhD
Associates
Min Hu, PhD
Michail Shipitsin, PhD
Jun Yao, PhD
相關基因：
CD44
Official Symbol: CD44 and Name: CD44 molecule (Indian blood group) [Homo sapiens]
Other Aliases: CDW44, CSPG8, ECMR-III, HCELL, IN, LHR, MC56, MDU2, MDU3, MGC10468, MIC4, MUTCH-I, Pgp1
Other Designations: CD44 antigen; CD44 antigen (Indian blood group); CD44 antigen (homing function and Indian blood group system); CD44 epithelial domain (CD44E); CDW44 antigen; GP90 lymphocyte homing/adhesion receptor; Hermes antigen; antigen gp90 homing receptor; cell adhesion molecule (CD44); cell surface glycoprotein CD44; chondroitin sulfate proteoglycan 8; extracellular matrix receptor-III; hematopoietic cell E- and L-selectin ligand; heparan sulfate proteoglycan; hyaluronate receptor; phagocytic glycoprotein I
Chromosome: 11; Location: 11p13
MIM: 107269
GeneID: 960
CD24
Official Symbol: CD24 and Name: CD24 molecule [Homo sapiens]
Other Aliases: CD24A
Other Designations: CD24 antigen; CD24 antigen (small cell lung carcinoma cluster 4 antigen)
Chromosome: 6; Location: 6q21
MIM: 600074
GeneID: 934
