Table 3 Differently expressed proteins in SW1116csc and SW1116 cells DISCUSSION Cancer is composed of heterogeneous cells. A cancer stem cell concept means that cancer cells exhibit a hierarchy and a small number of cancer cells are maintained as cancer stem cells able to renew and differentiate. selleck inhibitor Therefore, presumably all cancers come from stem cells and these cancer stem cells may be associated with metastasis, treatment resistance, and recurrence. Biologically distinct and relatively rare populations of tumor-initiating cells have been detected by several methods and markers in a variety of cancers. Putative breast cancer tumorigenic cells and CD44+ CD24-/ low ESA+ cells are able to drive tumor formation when a few hundred cells are injected into the mammary fat pad of NOD/SCID mice[13].
In addition, different populations of cancer cells derived from primary head and neck squamous cell carcinomas display a tumorigenic potential. A minority number of CD44+ cells give rise to new tumors in vivo[14]. Pancreatic cancer cells with the CD44+ CD24+ ESA+ phenotype have stem cell properties and exhibit a 100-fold higher tumorigenic potential than nontumorigenic cancer cells[15]. In this study, colon CSC were found in the CD133+ CD29+ fraction and colon cancer stem cells with this phenotype were biologically characterized by self-renewal, proliferation and differentiation. CD133 (prominin-1, PROM1) is a 5-transmembrane glycoprotein of 865 amino acids with a total molecular weight of 120 kDa.
It has been shown that CD133 antigen is expressed in undifferentiated endothelial progenitor cells[16], hematopoietic stem cells[17], fetal brain stem cells[18], embryonic epithelium[19], prostatic epithelial stem cells[20], and myogenic cells[21]. CD133 has also been found on cancer stem or tumor-initiating cells in cancers such as retinoblastoma[22], teratocarcinoma[23], leukemia[24], brain tumor[25], hepatocellular carcinoma[26], and colon cancer[27]. It was reported that a small number of CD133+ cells from primary colon cancer tissue have a tumorigenic potential in immunode?cient mice[4], indicating that CD133+ cells in colon cancer tissue have a high tumorigenic ability. Integrin is a non-covalently-bound heterodimeric cell adhesion molecule that links ECM to cytoskeleton. ��1 integrin family Batimastat (��1 integrins, CD29), the largest group of integrins, is composed of a ��1 and one of the 12 �� subunits and functions predominantly as cell-ECM adhesion. Both subunits have single hydrophobic transmembrane domains and transmit information from ECM context surrounding cells into outside-in signaling cells, while the extracellular binding activity of integrin is regulated from the inside of cells (inside-out signaling).