Nitric oxide and cGMP protein kinase (cGK) regulate dendritic-cell migration toward the lymph-node–directing chemokine CCL19

Abstract

Dendritic-cell (DC) migration to secondary lymphoid organs is crucial for the initiation of adaptive immune responses. Although LPS up-regulates CCR7 on DCs, a second signal is required to enable them to migrate toward the chemokine CCL19 (MIP-3␤). We found that the nitric oxide (NO) donor NOR4 provides a signal allowing LPS-stimulated DCs to migrate toward CCL19. NO affects DC migration through both the initial activation of the cGMP/cGMP kinase (cGMP/cGK) pathway and a long-term effect that reduced cGK activity via negative feedback. Indeed, migration of DCs toward CCL19, unlike migration toward CXCL12 (SDF-1␣), required inhibition of cGK. LPS increased both cGK expression and cGK activity as measured by phosphorylation of the key cGK target vasodilator-stimulated phosphoprotein (VASP). Because cGK phosphorylation of VASP can disrupt focal adhesions and inhibit cell migration, LPSinduced VASP phosphorylation may prevent DCs from migrating without a second signal. Long-term NOR4 treatment inhibited the increase in cGK-dependent VASP phosphorylation, releasing this brake so that DCs can migrate. NO has been implicated in the regulation of autoimmunity through its effect on T cells. Our results suggest that NO regulation of DC migration and cytokine production may contribute to the protective effects of NO in autoimmune disorders. IntroductionDendritic cells (DCs) activate naive T cells in peripheral lymphoid tissues and play a pivotal role in initiating and instructing adaptive immune responses. 1,2 At the site of infection where they take up antigens, DCs also contribute to innate immunity: They recognize and respond to common pathogen-associated molecular patterns (PAMPs) by releasing proinflammatory products that regulate other inflammatory cells. 3 In a later phase, recognition of PAMPs triggers a complex maturation program that results in the increase in DC antigen-presenting ability and responsiveness to chemokines like CCL19/MIP-3␤, which promote DC migration from peripheral tissues to secondary lymphoid organs. 4,5 The outcome of an immune response depends not only on the pathogen that activates DCs but also on various inflammationassociated factors that modulate DC maturation and determine whether DCs polarize T-cell development into T helper 1 (Th1)-, Th2-, or regulatory T-cell subsets. 6 Prostaglandin E2 (PGE2) and other inflammatory products that act through the cAMP/cAMP kinase (cAMP/cAK) signaling pathway can affect DC maturation and drive them toward a Th2-inducing program. [7][8][9] These agents also regulate DC chemokine and chemokines receptor expression; they down-regulate receptors for inflammatory chemokines like CCR5 while increasing CCR7 or CXCR4 receptors for CCL19/ MIP-3␤ and CXCL12/SDF-1␣, respectively. [10][11][12] Interestingly, inflammatory agents are required for mature DCs to be able to migrate toward certain chemokines. Even after monocyte-derived immature DCs (iDCs) are induced to mature and up-regulate CCR7, they remain unresponsive to CCL19 and do not migrate unless they are e...

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