Exposure of Human Primary Colon Carcinoma Cells to Anti-Fas Interactions Influences the Emergence of Pre-existing Fas-Resistant Metastatic Subpopulations

Abstract

Fas, an important death receptor-mediated signaling pathway, has been shown to be down-regulated during human colon tumorigenesis; however, how alterations in Fas expression influence the metastatic process remains unresolved. In mouse models, loss of Fas function was found to be both necessary and sufficient for tumor progression. In this study, we investigated the link between functional Fas status and malignant phenotype using a matched pair of naturally occurring primary (Fas-sensitive) and metastatic (Fas-resistant) human colon carcinoma cell lines in both in vitro and in vivo (xenograft) settings. Metastatic sublines were produced in vitro from the primary tumor cell line by functional elimination of Fas-responsive cells. Conversely, sublines derived from the primary tumor in vivo at distal metastatic sites were Fas-resistant. In contrast, simply disrupting the Fas pathway by molecular-based strategies in the Fas-sensitive primary tumor failed to achieve the same metastatic outcome. Interestingly, both in vitro- and in vivo-produced sublines resembled the naturally occurring metastatic population, based on functional and morphologic studies and genome-scale gene expression profiling. Overall, using this human colon carcinoma model, we: 1) showed that loss of Fas function was linked to, but alone was insufficient for, acquisition of a detectable metastatic phenotype; 2) demonstrated that metastatic subpopulations pre-existed within the heterogeneous primary tumor, and that anti-Fas interactions served as a selective pressure for their outgrowth; and 3) identified a large set of differentially expressed genes distinguishing the primary from metastatic malignant phenotypes. Thus, Fas-based interactions may represent a novel mechanism for the biologic or immunologic selection of certain types of Fas-resistant neoplastic clones with enhanced metastatic ability.

Fas-Negative Osteosarcoma Tumor Cells Are Selected during Metastasis to the Lungs: The Role of the Fas Pathway in the Metastatic Process of Osteosarcoma

“…Perhaps, in their models, the single attenuation of Fas signaling was not sufficient to promote metastasis and other alterations were needed to generate a more aggressive metastatic phenotype. In fact, this group later identified a large set of differentially expressed genes in primary tumor cells compared with their in vivo -selected highly metastatic subline (27).…”

The role of Fas ligand protein in the oxidative stress induced by azoxymethane on crypt colon of rats

“…Cells that have acquired resistances to apoptosis either before or as a result of mutational changes fail to be eliminated by apoptosis, and are in this way able to continue the progression towards a neoplastic phenotype [15][16][17][18][19][20][21] . Failure of apoptosis may be of particular importance in the development of colorectal cancer 15,[22][23][24] .…”

“…Fas downregulation might be a consequence of p53 mutation at later stages of colon tumour development because Fas is a target gene for transcriptional activation by p53. Transfection of wild-type p53 into various tumour cell lines has been shown to restore/ upregulate Fas expression [22][23][24] .…”

How tumours escape mass destruction

“…In fact, such Fas lo variants were not only more aggressive in vivo, but also significantly more refractory to CTL-adoptive immunotherapy (Liu et al, 2005b(Liu et al, , 2006. In addition, in both mouse and human solid tumour models, it was demonstrated that biological selection against Fas-responsive cells within parental or primary tumour cell lines, using surrogate sources of Fas engagement, generated Fas lo sub-populations with enhanced malignant ability (Liu et al, 2003;Liu and Abrams, 2003a (Liu et al, 2005a). Immune selection of Fas lo variants may thus be a novel mechanism of immune escape during the effector/target interaction within the local tumour microenvironment.…”

“…In the case of increased resistance to extrinsic cell death, such as Fas, this may occur through downmodulation of the receptor itself, defects in caspase family members or dysregulation of the signalling pathway due to the overexpression of key anti-apoptotic proteins, such as FLICE inhibitory proteins (FLIP), inhibitors of apoptosis or survivin, which also affect caspase activation. The potential importance of Fas loss of function in tumour escape and tumour progression reflects two important considerations in cancer biology and tumour immunology: (a) Fas downregulation has been noted in the progression of a range of human malignancies (Keane et al, 1996;Krammer et al, 1998;von Reyher et al, 1998;Owen-Schaub et al, 2000;Worth et al, 2002;Liu et al, 2003;Gordon et al, 2005); and (b) if Fas-mediated cytotoxicity is an important host defense mechanism during the effector phase of the immune reaction and if it becomes compromised, this could lead to the emergence of Fas-resistant (Fas lo ) tumour escape variants with potentially enhanced malignant capabilities. Fas lo variants have been shown to exhibit enhanced tumour growth and reduced sensitivity to CTL-based immunotherapy, as shown in mouse models of experimental lung metastasis (Liu et al, 2005b(Liu et al, , 2006.…”