谷报道：据《Cancer Cell》杂志2007年3月13日报道，Dana-Farber癌症研究所最新的研究对“肿瘤干细胞”假说提出了质疑，该假说认为，肿瘤组织内有少量可以自我复制的肿瘤干细胞，肿瘤干细胞在乳腺癌变过程中和癌症复发中起主导作用，清除肿瘤干细胞就可治愈癌症。
文章报道，科学家已经从一个乳腺癌组织标本中分离出两个遗传背景不同的细胞群，其中之一就是其他科学家坚信存在的乳腺癌肿瘤干细胞。文章资深作者Kornelia Polyak 指出，“如果全部的乳腺癌细胞源自同一个癌干细胞，那么仅需用一种药就可以治愈该病。但是根据实验结果，我们推测，乳腺癌细胞是来自一种干细胞样的祖细胞，是由这类细胞分化为遗传背景不均一的肿瘤细胞，因此必须对这两类细胞都进行治疗。”这两类细胞（干细胞样祖细胞和癌细胞），或许还有其它的，都与乳腺癌的癌变过程有关。研究者对这两类细胞进行基因扫描分析后，发现所谓的“肿瘤干细胞”与正常的干细胞很似，是由一个激活的分子通路诱导产生的。乳腺癌患者如果含有大量这种干细胞样细胞，其癌症复发的机率是相当高的。但像这种情况也有其积极的一面，因为这种肿瘤干细胞样细胞存在异常的信号活化通路，如目前已知道的TGF-β1信号转导通路，而实验已发现可以抑制信号活化通路的药物，现在这些药物正进入临床试验阶段，哈佛医学院Polyak副教授指出。因此，临床上使用这些信号活化通路抑制药物，再加上其它治疗，估计会改善由这类细胞产生的乳腺癌的预后。
肿瘤的形成是源于细胞的克隆演变还是肿瘤干细胞分化？细胞克隆演变是一个解释肿瘤形成的理论模型，该模型认为肿瘤细胞是经过长期的克隆演变筛选出来的：正常的细胞出现突变，产生了异常的子代细胞克隆，而各个子代细胞又突变产生更加异常的子代细胞克隆，如此循环，最终会产生大量的遗传背景不均一的细胞克隆，正常细胞变成了癌细胞，至此肿瘤就形成了。目前另外还有一个解释肿瘤形成的理论，其观点是单一的某种异常类型的成人干细胞产生并促使了肿瘤的形成，所以最终形成的肿瘤其细胞的遗传背景是均一的，乳腺癌的产生就是这样。肿瘤干细胞假说认为，用药物很难将这些少量的可自我复制的肿瘤干细胞杀灭，也许肿瘤干细胞这种耐药性可解析为何经过成功治疗的乳腺癌患者仍会经常复发。2003年科学家已从患者肿瘤组织里分离出所谓的乳腺癌肿瘤干细胞，其细胞表面分子CD44认为是肿瘤干细胞特异性分子，但CD44分子也是正常乳腺细胞的分子标志。CD44阳性细胞输入给免疫缺陷的小鼠后可形成乳腺肿瘤。科学家还发现与之紧密相关的细胞为CD22阳性，怀疑其是CD44阳性细胞产生的子代细胞。
Polyak和Michail Shipitsin领导的研究小组采用基因扫描技术分析这两类细胞的关系。他们分别从正常乳腺上皮、胸腔积液、乳腺癌原位癌患者标本中分离出CD24阳性和 CD44阳性细胞，再制备成各自的基因文库进行基因扫描。最后的实验结果与细胞克隆演化模型理论更相符合，也就是说，CD24阳性细胞和 CD44阳性细胞在遗传背景上并非等同，仅是相似而已，但按肿瘤干细胞假说的观点，CD44阳性细胞为肿瘤干细胞，CD24阳性细胞是其子代细胞，那么两者在遗传背景应该是一致的。“尽管CD44阳性细胞可表达多种干细胞分子标志，但是，由同一肿瘤组织分离得到的CD24阳性和 CD44阳性细胞两者在遗传背景上是有差异的，这一结果对肿瘤干细胞假说构成了质疑，同时支持细胞克隆演化模型，因为该理论可以很好地解释肿瘤异质性这一现象。”作者在论文中写道。
Polyak研究小组进一步发现，活化的TGF-β1信号转导通路可诱导CD44阳性细胞产生，而CD24阳性细胞则没有这种现象，为此，他们说，“临床上，肿瘤细胞表达CD44分子的较表达CD24的预后更差，但是，CD44阳性细胞反而可以提供TGF-β1信号转导通路为靶点进行治疗。”
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.
原文出处：
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)
作者简介：
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
相关基因：
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
