L-selectin activates the Ras pathway via the tyrosine kinase p56lck.
Selectins mediate rolling, the initial step of leukocyte adhesion to endothelial cells [Springer, T. A. (1995) Annu. Rev. Physiol. 57, 827-872 and Butcher, E. C. (1991) Cell 67, 1033-1036]. In this study we show that L-selectin triggering of Jurkat cells using different antibodies or glycomimetics resulted in activation of the src-tyrosine kinase p56lck; tyrosine phosphorylation of intracellular proteins, in particular mitogen-activating protein kinase and L-selectin; and association of Grb2/Sos with L-selectin. This association correlated with an activation of p21Ras, mitogen-activating protein kinase, Rac2, and a transient increase of 2-O synthesis. Stimulation of the Ras pathway by L-selectin requires functional p56lck, since p56lck-deficient Jurkat cells (JCaM1.6) do not show tyrosine phosphorylation, association of L-selectin with Grb2/Sos, and activation of Ras upon L-selectin triggering. Transfection of JCaM1.6 cells with p56lck reconstitutes the observed signaling events. Genetic inhibition of Ras or Rac2 prevented Rac2 stimulation and 2-O synthesis, respectively. The specificity and the physiological significance of the observed signaling cascade is indicated by stimulation of L-selectin-transfected P815, L-selectin-positive CEM or peripheral blood lymphocytes resulting in the same activation events as in Jurkat cells. Our results point to a signaling cascade from L-selectin via p56lck, Grb2/Sos, Ras, and Rac2 to 2-O.
Brenner
B
B
Department of Pediatrics, University of Heidelberg, Germany.
Gulbins
E
E
Schlottmann
K
K
Koppenhoefer
U
U
Busch
G L
GL
Walzog
B
B
Steinhausen
M
M
Coggeshall
K M
KM
Linderkamp
O
O
Lang
F
F
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006801:Humans; D019041:L-Selectin / Q000096:biosynthesis / Q000378:metabolism*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D012515:Mast-Cell Sarcoma; D051379:Mice; D019000:Phosphotyrosine / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013481:Superoxides / Q000378:metabolism; D013601:T-Lymphocytes; D014162:Transfection; D020744:rac GTP-Binding Proteins; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
D020690:GTPase-Activating Proteins; D011506:Proteins; D011994:Recombinant Proteins; D020703:ras GTPase-Activating Proteins; D013481:Superoxides; D019041:L-Selectin; D019000:Phosphotyrosine; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D019061:src-Family Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; D018631:ras Proteins