Investigation of the mechanisms of tissue factor-mediated evasion of tumour cells from cellular cytotoxicity.
OBJECTIVE
We previously reported that overexpression of tissue factor (TF) protected HT29 tumour cells from cellular cytotoxicity through a mechanism requiring the presence of the cytoplasmic domain of TF. In this investigation the mechanism of TF-mediated immune evasion has been examined.


METHODS
The influence of alanine-substitution at Ser253 and Ser258 of TF (TF(Ala253) and TF( Ala258)) on the induction of cytotoxic evasion, as well as expression of vascular cell adhesion molecule-1 and intra-cellular adhesion molecule-1 (VCAM-1 and ICAM-1) was investigated. Moreover, we examined the effect of transfection of four 20-mer peptides, corresponding to the C-terminal residues of TF, with different phosphorylation states, on promotion of evasion from cell cytotoxicity.


RESULTS
Cells overexpressing TF(Ala258) and to a lesser extent overexpressing TF(Ala253,) exhibited a reduced ability to evade cellular cytotoxicity compared to cells overexpressing the wild-type TF. Furthermore, the increase in protection acquired was greatest on transfection of Ser258-phosphsorylated form of the cytoplasmic peptide, lower in double-phosphorylated and Ser253-phosphorylated peptides respectively, and lowest in the unphosphorylated form. Finally, the expression of VCAM-1 mRNA as well as surface antigen was reduced on overexpression of TF(wt) but was partially reverted in the cells transfected to overexpress TF(Ala253) or TF(Ala258).


CONCLUSIONS
These data show that the phosphorylation of TF at Ser258 and to a lesser extent Ser253, plays an essential role in the protective influence of TF on immune evasion by tumour cells, and that the mechanism could involve the downregulation of key surface antigens, such as adhesion proteins, involved in cell:cell interaction.
Li
Chao
C
Biomedical Section, Department of Biological Sciences, University of Hull, Cottingham Road, Hull, HU6 7RX, UK.
Collier
Mary E W
ME
Frentzou
G Alkisitis
GA
Greenman
John
J
Ettelaie
Camille
C
D000409:Alanine / Q000737:chemistry; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007107:Immune System; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D009362:Neoplasm Metastasis; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D012694:Serine / Q000737:chemistry; D013925:Thromboplastin / Q000378:metabolism*; D014162:Transfection; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D010455:Peptides; D019010:Vascular Cell Adhesion Molecule-1; D012694:Serine; D013925:Thromboplastin; D000409:Alanine