Functional analysis of Ran/TC4 as a protein regulating T-cell costimulation.
Antigen (Ag)-triggered activation of T cells requires engagement of both the T-cell Ag receptor and a costimulatory receptor, for which CD28 can function as a prototypical example. CD80 and CD86 represent ligands for this receptor, and although they are present on professional Ag-presenting cells, these molecules are absent from most tumors. Yet some tumors are still able to costimulate a T-cell response, while others cannot. Therefore, a key question concerns the molecular basis for the costimulation of T cells by those tumor cells not expressing the CD28 ligands CD80 and CD86. Upon screening a cDNA library of such a tumor cell line in a transient COS cell transfection assay for costimulatory activity, we identified Ran/TC4 as a protein whose overexpression results in costimulatory activity. Ran/TC4 is a ubiquitously expressed member of the Ras gene superfamily of small guanosine triphosphate-binding proteins and is involved in nuclear transport; Ran/TC4 cDNA-transfected COS cells specifically costimulate CD8 T cells and not CD4 T cells. Transfection of Ran/TC4 into the costimulation-deficient murine RMA lymphoma cell line introduced costimulatory capacity for CD8 T cells and resulted in markedly elevated levels of nuclear Ran/TC4 protein expression. In addition, in vivo priming of mice with Ran/TC4-transfected RMA cells induced protection against wild-type (wt) RMA tumor cells. Ran/TC4-transfected RMA cells and wt RMA tumor cells exhibit comparable in vivo growth rates in mice lacking T and B cells, and Ran/TC4-mediated tumor rejection thus involves B and/or T cells. This possibility is substantiated by the observation that T cells from normal mice challenged with Ran/TC4-transfected RMA cells can mount a cytotoxic T-cell response not only against the Ran/TC4-transfected tumor cells but also against wt RMA tumor cells. Based on these results, we conclude that gene transfer-mediated elevations in Ran/TC4 can confer costimulatory function for CD8 T cells to tumor cells. This finding suggests a novel application of Ran/TC4 as a protein capable of regulating costimulation in tumor cells.
Nieland
J D
JD
Division of Immunology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Huis, Amsterdam.
Haks
M C
MC
Kremers
B L
BL
Leupers
T J
TJ
Bakker
A Q
AQ
Offringa
R
R
Kruisbeek
A M
AM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism*; D019556:COS Cells / Q000378:metabolism; D015197:Carcinogenicity Tests; D003001:Cloning, Molecular; D015972:Gene Expression Regulation, Neoplastic; D016399:Lymphoma, T-Cell / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D020931:ran GTP-Binding Protein
D009687:Nuclear Proteins; D020931:ran GTP-Binding Protein