CCL21 mediates CD4+ T-cell costimulation via a DOCK2/Rac-dependent pathway.
CD4(+) T cells use the chemokine receptor CCR7 to home to and migrate within lymphoid tissue, where T-cell activation takes place. Using primary T-cell receptor (TCR)-transgenic (tg) CD4(+) T cells, we explored the effect of CCR7 ligands, in particular CCL21, on T-cell activation. We found that the presence of CCL21 during early time points strongly increased in vitro T-cell proliferation after TCR stimulation, correlating with increased expression of early activation markers. CCL21 costimulation resulted in increased Ras- and Rac-GTP formation and enhanced phosphorylation of Akt, MEK, and ERK but not p38 or JNK. Kinase-dead PI3Kdelta(D910A/D910A) or PI3Kgamma-deficient TCR-tg CD4(+) T cells showed similar responsiveness to CCL21 costimulation as control CD4(+) T cells. Conversely, deficiency in the Rac guanine exchange factor DOCK2 significantly impaired CCL21-mediated costimulation in TCR-tg CD4(+) T cells, concomitant with impaired Rac- but not Ras-GTP formation. Using lymph node slices for live monitoring of T-cell behavior and activation, we found that G protein-coupled receptor signaling was required for early CD69 expression but not for Ca(2+) signaling. Our data suggest that the presence of CCL21 during early TCR signaling lowers the activation threshold through Ras- and Rac-dependent pathways leading to increased ERK phosphorylation.
Gollmer
Kathrin
K
Theodor Kocher Institute, University of Bern, Freiestrasse 1, Bern, Switzerland.
Asperti-Boursin
François
F
Tanaka
Yoshihiko
Y
Okkenhaug
Klaus
K
Vanhaesebroeck
Bart
B
Peterson
Jeffrey R
JR
Fukui
Yoshinori
Y
Donnadieu
Emmanuel
E
Stein
Jens V
JV
D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000502:physiology*; D049109:Cell Proliferation; D054421:Chemokine CCL21 / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D008198:Lymph Nodes; D008213:Lymphocyte Activation; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D015398:Signal Transduction; D020744:rac GTP-Binding Proteins / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism
D054421:Chemokine CCL21; C471356:DOCK2 protein, mouse; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D048049:Extracellular Signal-Regulated MAP Kinases; D020744:rac GTP-Binding Proteins; D018631:ras Proteins