Autocrine secretion of Fas ligand shields tumor cells from Fas-mediated killing by cytotoxic lymphocytes

Decreased total lymphocyte counts in pancreatic cancer: an index of adverse outcome

OBJECTIVES

An impaired host immunity might concur in determining the dismal prognosis of patients with pancreatic cancer (PC). Our aim was to ascertain whether the immunophenotype pattern of blood lymphocytes in PC correlates with tumor stage, grade, or survival.

METHODS

We studied 115 patients with PC, 44 with chronic pancreatitis (CP), 23 with tumors of the pancreatico-biliary tract, and 34 healthy controls (CS). Survival data were available for 77 patients with PC. Lymphocyte subsets were determined by fluorescent activated cell sorter (FACS) analysis.

RESULTS

In patients with PC, total lymphocyte counts were lower than in CP or CS, and CD8 lymphocyte subset levels were higher with respect to CS. Lower circulating lymphocytes were found in advanced PC stages (IIB-IV; chi2 = 11.55, P < 0.05) compared with stages 0 to IIA. Cox regression analysis, made considering total lymphocyte counts and tumor stage as covariates, was found to be significant for both tumor stage (P < 0.001) and total lymphocyte counts (P < 0.05).

CONCLUSIONS

The reduction of total lymphocytes in blood is the main immunologic change in advanced PC. The survival of these patients depends mainly on tumor stage, but it is also affected by the number of circulating lymphocytes, suggesting that the immune system plays an important role in pancreatic adenocarcinoma immunosurveillance and immunoediting.

Close localization of DAP-kinase positive tumour-associated macrophages and apoptotic colorectal cancer cells

The death-associated protein kinase (DAP-kinase) is a cytoskeleton-associated protein crucially involved in the induction of early apoptotic pathways. Aberrant hypermethylation of the DAP-kinase promoter plays a major role in tumorigenesis. We aimed to investigate the inactivation of DAP-kinase and its association with apoptotic cell death in 94 colorectal carcinomas. DAP-kinase promoter hypermethylation and mRNA expression were investigated using methylation-specific PCR and real-time RT-PCR, respectively. The expression of DAP-kinase, Fas, and Fas-ligand (FasL) proteins was studied by immunohistochemistry and immunofluorescence. Apoptosis of tumour cells was investigated using the TUNEL assay. DAP-kinase was expressed in tumour cells and tumour-invading macrophages and was closely associated with high numbers of apoptotic tumour cells. DAP-kinase expression co-localized with FasL overexpression in tumour-associated macrophages, and aberrant promoter hypermethylation was verified in more than 50% of carcinomas. There was a tendency for proximal tumours to show DAP-kinase promoter methylation more frequently (p = 0.07). Promoter methylation resulted in a decrease or loss of DAP-kinase protein expression in tumour cells and tumour-associated macrophages. Simultaneously, a decreased apoptotic count and loss of Fas/FasL expression was observed in tumour cells. Our study is the first to demonstrate DAP-kinase expression in invading tumour-associated macrophages in colorectal cancer. The presence of similar expression levels of DAP-kinase in tumour cells and associated macrophages, and their dependence on the promoter methylation status of the tumour cells, suggests cross talk between these cell types during apoptotic cell death.

Binding of the Intracellular Fas Ligand (FasL) Domain to the Adaptor Protein PSTPIP Results in a Cytoplasmic Localization of FasL

The tumor necrosis factor family member Fas ligand (FasL) induces apoptosis in Fas receptor-expressing target cells and is an important cytotoxic effector molecule used by CTL- and NK-cells. In these hematopoietic cells, newly synthesized FasL is stored in specialized secretory lysosomes and only delivered to the cell surface upon activation and target cell recognition. FasL contains an 80-amino acid-long cytoplasmic tail, which includes a proline-rich domain as a bona fide Src homology 3 domain-binding site. This proline-rich domain has been implicated in FasL sorting to secretory lysosomes, and it may also be important for reverse signaling via FasL, which has been described to influence T-cell activation. Here we report the identification of the Src homology 3 domain-containing adaptor protein PSTPIP as a FasL-interacting partner, which binds to the proline-rich domain. PSTPIP co-expression leads to an increased intracellular localization of Fas ligand, thereby regulating extracellular availability and cytotoxic activity of the molecule. In addition, we demonstrate recruitment of the tyrosine phosphatase PTP-PEST by PSTPIP into FasL.PSTPIP.PTP-PEST complexes which may contribute to FasL reverse signaling.

Mechanism of counterattack of colorectal cancer cell by Fas/Fas ligand system

AIM: To determine the role of Fas/Fas ligand (FasL) in the immune escape of colon cancer cells.

METHODS: Immunohistochemistry was used to observe the expression of Fas and FasL in the tissues of colon cancer patients.In situ hybridization was used to detect the localization of FasL mRNA expression in cancer tissues. Terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) assay and CD45 staining were performed to detect the apoptosis of tumor-infiltrating lymphocytes (TILs). Co-culture assays of colon cancer cells (SW480) and Jurkat cells (Fas-sensitive cells) were performed to observe the counterattack of colon cancer cells to lymphocytes.

RESULTS: Of 53 cases of colon carcinomas, 23 cases (43.4%) expressed Fas which was significantly lower as compared to the normal colonic mucosa (73.3%, P<0.01), and 45 cases (84.9%) of colon carcinomas expressed FasL, whereas only two cases (3.75%) in normal mucosa expressed FasL. FasL expression in the colon cancer cells was found to be associated with increased cell death of TILs. The apoptotic rate of TIL in the FasL-positive staining regions of tumor cells was significantly higher than that in the FasL-negative staining region (54.84 ± 2.79% vs 25.73 ± 1.98%, P<0.01). The co-culture of SW480 cells and Jurkat cells confirmed the function of FasL on the SW480 cells. The apoptotic rates of Jurkat cells were found to be related with the amount of SW480 cells.

CONCLUSION: Colon cancer cells can escape the immune surveillance and killing via decreasing Fas expression, and can counterattack the immune system via increasing FasL expression. Fas/FasL can serve as potential targets for effective antitumor therapy.

FAS/FAS Ligand Ratio: A Marker of Oxaliplatin-Based Intrinsic and Acquired Resistance in Advanced Colorectal Cancer

PURPOSE

Oxaliplatin-5-fluorouracil combinations have increased responses in first-line therapy up to 40% in advanced colorectal cancer. Unfortunately, those patients who will respond are unknown and initially sensitive patients become rapidly resistant to current therapies. FAS (CD95) and FAS ligand (FASL; CD95L) have been implicated in chemosensitivity through leading to apoptosis in response to DNA-damaging drugs. Whereas the proapoptotic role of FAS and FASL is well characterized, the function of their soluble forms as predictors of chemosensitivity remains unknown.

PATIENTS AND METHODS

Blood samples were obtained from 68 patients with advanced colorectal cancer who received oxaliplatin-5-fluorouracil combinations in first-line therapy. Computed tomographic scans were done every 3 months and responses were evaluated by Response Evaluation Criteria in Solid Tumors criteria. ELISA soluble FAS and soluble FASL analysis were done before treatment and every 3 months until disease progression. Ratios between soluble FAS and soluble FASL were established and its values and variations through time were related to treatment responses.

RESULTS

We found a significant increase in soluble FAS levels and a significant decrease in FASL at 3 months compared with baseline (13.2 versus 10.02 ng/mL; P=0.0001; 0.07 versus 0.14 ng/mL; P=0.007, respectively). A significant increase in the soluble FASL levels up to 9 months (fourth to fifth extractions; 0.26 ng/mL) of therapy compared with first to third extractions (0.11 ng/mL; P=0.003) was also found. A random effect regression statistical model determined that >1.2-fold increase in soluble FAS/soluble FASL ratio was a marker of chemosensitivity (P = 0.001).

CONCLUSIONS

These data strongly indicate that an increment of soluble FAS/soluble FASL ratio after treatment could be an excellent marker of chemosensitivity in colorectal cancer. On the other hand, a decreased ratio after treatment can be a predictor of chemoresistance despite an initial response.

Considering Fas ligand as a target for therapy

About a decade ago, the death factor Fas ligand (FasL) was identified as the natural trigger of Fas/CD95-dependent apoptosis and as an inducer of Fas-dependent activation-induced cell death. Meanwhile, it is known that this molecule not only contributes to target cell lysis in the immune system but also to the establishment of immune privilege and tumour survival. Because delivering a specific antiproliferative signal to T lymphocytes is of major biomedical interest, the FasL/Fas system has gained much attention over the last few years. However, only recently it became evident that the biology of FasL is more complex than initially anticipated. FasL displays a complex pattern of inducible and constitutive expression associated with a number of different functions as a death factor or a co-stimulatory/accessory molecule in lymphocyte activation. Thus, side effects are likely to occur following systemic administration of, for example, anti-FasL medication, not only because of the constitutive FasL expression on cells within immune privileged tissues and vascular endothelium. In addition, FasL comes in different forms: as a surface molecule, as a protease-shed soluble variant or secreted in vesicles. Because increased levels of soluble FasL (sFasL) have been determined in various immunological and non-immunological diseases, it has been suggested that sFasL might serve as a prognostic or diagnostic marker even though the pathophysiological cause for its enhanced production is hardly known in most cases. This review summarises the current facts and ideas about the clinical and pharmacological potential of FasL and sFasL as targets for therapeutic interventions.