Identification of a distinct side population of cancer cells in the Cal-51 human breast carcinoma cell line.
"Side population" (SP) cells, which pump out the fluorescent dye H33342 via the ABCG2 transporter, define a putative stem/progenitor cell population in the mammary gland. Breast cancer SP cells recently isolated from the MCF-7 cell line possess similar properties and may represent stem cell-like cancer cells. This study extends SP cell analysis to a broad panel of human breast cancer cell lines and investigates the expression of differentiation-associated markers in isolated cancer SP cells. Expression of ABCG2 was determined in 16 breast cancer cell lines by quantitative RT-PCR, Western blotting and immunohistochemistry. Subsequently, all cell lines were screened for the presence of SP cells. Human breast cancer cell lines commonly express ABCG2. ABCG2-immunoreactivity was clearly restricted to rare cancer cells in several cell lines including Cal-51. Analysis of H33342-labeled Cal-51 cells revealed a small fraction of putative SP cells accounting for one percent of all cells. The genuine nature of Cal-51 SP cells was unambiguously verified by demonstrating a 30-fold increased ABCG2-expression in isolated Cal-51 SP cells. During in vitro expansion, Cal-51 SP cells generated heterologous non-SP (NSP) cells and ABCG2-expression declined dramatically. In contrast, NSP cells failed to sustain proliferation. Freshly isolated Cal-51 SP cells also exhibited increased expression of Muc1 and CALLA. Noteworthy, non-malignant mammary epithelial SP cells lack these differentiation markers, highlighting fundamental differences between non-malignant and breast cancer-derived SP cells. In summary, we established Cal-51 SP cells as a novel in vitro model to study differential gene expression in breast cancer-derived SP and NSP cells.
Christgen
Matthias
M
Institute of Pathology, Hannover Medical School, Carl-Neuberg-Str. 1, 30625, Hannover, Germany. Christgen.Matthias@MH-Hannover.de
Ballmaier
Matthias
M
Bruchhardt
Henriette
H
von Wasielewski
Reinhard
R
Kreipe
Hans
H
Lehmann
Ulrich
U
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D002454:Cell Differentiation; D048708:Cell Growth Processes / Q000502:physiology; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D009363:Neoplasm Proteins; D012333:RNA, Messenger