Colon carcinoma is one of the leading causes of death from cancer and is characterized by a heterogenic pool of cells with distinct differentiation patterns. Recently, it was reported that a population of undifferentiated cells from a primary tumor, so-called cancer stem cells (CSC), can reconstitute the original tumor on xenotransplantation. Here, we show that spheroid cultures of these colon CSCs contain expression of CD133, CD166, CD44, CD29, CD24, Lgr5, and nuclear β-catenin, which have all been suggested to mark the (cancer) stem cell population. More importantly, by using these spheroid cultures or freshly isolated tumor cells from multiple colon carcinomas, we now provide compelling evidence to indicate that the capacity to propagate a tumor with all differentiated progeny resides in a single CSC. Single-cell-cloned CSCs can form an adenocarcinoma on xenotransplantation but do not generate the stroma within these tumors. Moreover, they can self-renew and are capable of multilineage differentiation. Further analysis indicated that the lineage decision is dictated by phosphoinositide 3-kinase (PI3K) signaling in CSCs. These data support the hypothesis that tumor hierarchy can be traced back to a single CSC that contains multilineage differentiation capacity, and provides clues to the regulation of differentiation in colon cancers in vivo .

Colon cancer stem cells (CSC) can be identified with AC133, an antibody that detects an epitope on CD133. However, recent evidence suggests that expression of CD133 is not restricted to CSCs, but is also expressed on differentiated tumor cells. Intriguingly, we observed that detection of the AC133 epitope on the cell surface decreased upon differentiation of CSC in a manner that correlated with loss of clonogenicity. However, this event did not coincide with a change in CD133 promoter activity, mRNA, splice variant, protein expression, or even cell surface expression of CD133. In contrast, we noted that with CSC differentiation, a change occured in CD133 glycosylation. Thus, AC133 may detect a glycosylated epitope, or differential glycosylation may cause CD133 to be retained inside the cell. We found that AC133 could effectively detect CD133 glycosylation mutants or bacterially expressed unglycosylated CD133. Moreover, cell surface biotinylation experiments revealed that differentially glycosylated CD133 could be detected on the membrane of differentiated tumor cells. Taken together, our results argue that CD133 is a cell surface molecule that is expressed on both CSC and differentiated tumor cells, but is probably differentially folded as a result of differential glycosylation to mask specific epitopes. In summary, we conclude that AC133 can be used to detect cancer stem cells, but that results from the use of this antibody should be interpreted with caution. Cancer Res; 70(2); 719–29

The involvement of the death adaptor protein FADD and the apoptosis‐initiating caspase‐8 in CD95 and TRAIL death signalling has recently been demonstrated by the analysis of the native death‐inducing signalling complex (DISC) that forms upon ligand‐induced receptor cross‐linking. However, the role of caspase‐10, the other death‐effector‐domain‐containing caspase besides caspase‐8, in death receptor signalling has been controversial. Here we show that caspase‐10 is recruited not only to the native TRAIL DISC but also to the native CD95 DISC, and that FADD is necessary for its recruitment to and activation at these two protein complexes. With respect to the function of caspase‐10, we show that it is not required for apoptosis induction. In addition, caspase‐10 can not substitute for caspase‐8, as the defect in apoptosis induction observed in caspase‐8‐deficient cells could not be rescued by overexpression of caspase‐10. Finally, we demonstrate that caspase‐10 is cleaved during CD95‐induced apoptosis of activated T cells. These results show that caspase‐10 activation occurs in primary cells, but that its function differs from that of caspase‐8.