JCI - CD133 expression is not restricted to stem cells, and both CD133+ and CD133– metastatic colon cancer cells initiate tumors

CD133 expression is not restricted to stem cells, and both CD133⁺ and CD133^– metastatic colon cancer cells initiate tumors

Sergey V. Shmelkov, Jason M. Butler, Andrea T. Hooper, Adilia Hormigo, Jared Kushner, Till Milde, Ryan St. Clair, Muhamed Baljevic, Ian White, David K. Jin, Amy Chadburn, Andrew J. Murphy, David M. Valenzuela, Nicholas W. Gale, Gavin Thurston, George D. Yancopoulos, Michael D’Angelica, Nancy Kemeny, David Lyden, Shahin Rafii

Published in Volume 118, Issue 6

J Clin Invest. 2008; 118(6):2111–2120 doi:10.1172/JCI34401

Abstract | Full text | PDF | Supplemental material

C olon cancer stem cells are believed to originate from a rare population of putative CD133⁺ intestinal stem cells. Recent publications suggest that a small subset of colon cancer cells expresses CD133, and that only these CD133⁺ cancer cells are capable of tumor initiation. However, the precise contribution of CD133⁺ tumor-initiating cells in mediating colon cancer metastasis remains unknown. Therefore, to temporally and spatially track the expression of CD133 in adult mice and during tumorigenesis, we generated a knockin lacZ reporter mouse (CD133^lacZ/+), in which the expression of lacZ is driven by the endogenous CD133 promoters. Using this model and immunostaining, we discovered that CD133 expression in colon is not restricted to stem cells; on the contrary, CD133 is ubiquitously expressed on differentiated colonic epithelium in both adult mice and humans. Using Il10^–/–CD133^lacZ mice, in which chronic inflammation in colon leads to adenocarcinomas, we demonstrated that CD133 is expressed on a full gamut of colonic tumor cells, which express epithelial cell adhesion molecule (EpCAM). Similarly, CD133 is widely expressed by human primary colon cancer epithelial cells, whereas the CD133^– population is composed mostly of stromal and inflammatory cells. Conversely, CD133 expression does not identify the entire population of epithelial and tumor-initiating cells in human metastatic colon cancer. Indeed, both CD133⁺ and CD133^– metastatic tumor subpopulations formed colonospheres in in vitro cultures and were capable of long-term tumorigenesis in a NOD/SCID serial xenotransplantation model. Moreover, metastatic CD133^– cells form more aggressive tumors and express typical phenotypic markers of cancer-initiating cells, including CD44 (CD44⁺CD24^–), whereas the CD133⁺ fraction is composed of CD44^lowCD24⁺ cells. Collectively, our data suggest that CD133 expression is not restricted to intestinal stem or cancer-initiating cells, and during the metastatic transition, CD133⁺ tumor cells might give rise to the more aggressive CD133^–subset, which is also capable of tumor initiation in NOD/SCID mice.

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Figure 2

CD133 expression identifies differentiated luminal epithelium in organs with hollow cavities.

(A–D) CD133 expression in bile ducts of murine liver. X-gal staining (which reflects β-galactosidase expression) of CD133^lacZ/+ mouse liver (A) and immunohistochemistry of wild-type mouse liver with anti-CD133 antibody (B) localize CD133 expression to a columnar cells within the hepatic triad morphologically defined as a bile duct (BD). Costaining with X-gal and anti-CD31 antibody (C) and coimmunofluorescence with anti-CD133 (red) and anti-CD31 antibodies (green) (D) demonstrate that CD133 is not expressed on the vessels of hepatic triads. Original magnification, ×200 (A, inset); ×400 (B and C, insets). (E–H) CD133 expression in pancreatic ducts. X-gal staining of CD133^lacZ/+ mouse pancreas (E) and immunohistochemistry of wild-type mouse pancreas with anti-CD133 antibody (F) localize CD133 expression to a ductal epithelium. Costaining with X-gal and anti-CD31 antibody (G) and coimmunofluorescence with anti-CD133 (red) and anti-CD31 antibodies (green) (H) demonstrate that CD133 is not expressed on pancreatic vessels. (I–L) CD133 expression in bronchus. X-gal staining of CD133^lacZ/+ mouse lung (I) and immunohistochemistry of wild-type mouse lung with anti-CD133 antibody (J) localize CD133 expression ubiquitously to all of the ciliated bronchial epithelium. Costaining with X-gal and anti-CD31 antibody (K) and coimmunofluorescence with anti-CD133 (red) and anti-CD31 antibodies (green) (L) demonstrate that CD133 is not expressed on the mature vessels in lungs. BRN, bronchus; BV, blood vessel; CV, central vein; PD, pancreatic duct; PV, portal vein. Scale bar: 50 μm.