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Src-dependent Syk activation controls CD69-mediated signaling and function on human NK cells
Simona Pisegna1, Alessandra Zingoni, Gianluca Pirozzi
1Department of Experimental Medicine and Pathology, Istituto Pasteur-Fondazione Cenci Bolognetti, University La Sapienza, Rome, Italy.
Abstract:
CD69 C-type lectin receptor represents a functional triggering molecule on activated NK cells, capable of directing their natural killing function. The receptor-proximal signaling pathways activated by CD69 cross-linking and involved in CD69-mediated cytotoxic activity are still poorly understood. Here we show that CD69 engagement leads to the rapid and selective activation of the tyrosine kinase Syk, but not of the closely related member of the same family, ZAP70, in IL-2-activated human NK cells. Our results indicate the requirement for Src family kinases in the CD69-triggered activation of Syk and suggest a role for Lck in this event. We also demonstrate that Syk and Src family tyrosine kinases control the CD69-triggered tyrosine phosphorylation and activation of phospholipase Cgamma2 and the Rho family-specific exchange factor Vav1 and are responsible for CD69-triggered cytotoxicity of activated NK cells. The same CD69-activated signaling pathways are also observed in an RBL transfectant clone, constitutively expressing the receptor. These data demonstrate for the first time that the CD69 receptor functionally couples to the activation of Src family tyrosine kinases, which, by inducing Syk activation, initiate downstream signaling pathways and regulate CD69-triggered functions on human NK cells.
Insights
CD69 engagement activates the tyrosine kinase Syk, not ZAP70, in human NK cells. This pathway, involving Src family kinases, controls CD69-mediated cytotoxicity.
Area of Science:
- Immunology
- Cell Signaling
Background:
- CD69 is a C-type lectin receptor on activated NK cells that triggers cytotoxic activity.
- The precise signaling pathways downstream of CD69 remain incompletely understood.
Purpose of the Study:
- To elucidate the proximal signaling events initiated by CD69 engagement in human NK cells.
- To identify the key kinases and downstream effectors involved in CD69-mediated cytotoxicity.
Main Methods:
- Utilized IL-2-activated human NK cells and an RBL transfectant clone expressing CD69.
- Investigated tyrosine kinase activation (Syk, ZAP70, Src family kinases) upon CD69 cross-linking.
- Assessed activation of phospholipase Cgamma2 and Vav1, and measured CD69-triggered cytotoxicity.
Main Results:
- CD69 engagement rapidly and selectively activated Syk, but not ZAP70.
- Src family kinases, including Lck, were required for CD69-induced Syk activation.
- Syk and Src family kinases mediated CD69-triggered phosphorylation and activation of phospholipase Cgamma2 and Vav1, leading to cytotoxicity.
Conclusions:
- CD69 functionally couples to Src family tyrosine kinases, initiating Syk activation.
- This signaling cascade is crucial for regulating CD69-triggered cytotoxicity in human NK cells.