Tumour-expressed tissue factor inhibits cellular cytotoxicity.
OBJECTIVE
The association between tissue factor (TF) expression and increased rate of tumour metastasis is well established. In this study, we have examined the hypothesis that the expression of TF by disseminated tumour cells confers protection against immune recognition and cytotoxicity.


METHODS
A hybrid EGFP-TF protein was expressed in HT29 colon carcinoma and K562 lymphoblast cell lines. To assess the cytotoxic activity against tumour cells over-expressing TF, a novel method was used, based on the direct measurement of fluorescently labelled HT29 or K562 target cells.


RESULTS
Upon challenge with peripheral blood mononuclear cells (PBMC), tumour cells expressing TF partially evaded cellular cytotoxicity (Delta=15-40% reduction in cytotoxicity). Moreover, the influence of TF was not primarily dependent on its procoagulant function, although the inclusion of 20% (v/v) plasma did lower the rate of cytotoxicity against untransfected cells. However, expression of a truncated form of TF, devoid of the cytoplasmic domain, did not mediate any degree of inhibition of cytotoxicity, suggesting that the protective function of TF is principally due to this domain.


CONCLUSIONS
We conclude that TF can promote immune evasion in tumour cells expressing this protein leading to increased survival and therefore metastatic rate in such cells.
Li
Chao
C
Biomedical Section, Department of Biological Sciences, University of Hull, Cottingham Road, HU6 7RX, Hull, UK.
Colman
Lucy M
LM
Collier
Mary E W
ME
Dyer
Charlotte E
CE
Greenman
John
J
Ettelaie
Camille
C
D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000473:pathology; D003593:Cytoplasm / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020014:K562 Cells; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism*; D009362:Neoplasm Metastasis; D017434:Protein Structure, Tertiary; D011517:Prothrombin Time; D013925:Thromboplastin / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
D013925:Thromboplastin