CCR7 is necessary to direct dendritic cells (DCs) to secondary lymphoid nodes and to elicit an adaptative immune response. Despite its importance, little is known about the molecular mechanisms used by CCR7 to direct DCs to lymph nodes. In addition to chemotaxis, CCR7 regulates the migratory speed of DCs. We investigated the intracellular pathways that regulate CCR7-dependent chemotaxis and migratory speed. We found that CCR7 induced a Gi-dependent activation of MAPK members ERK1/2, JNK, and p38, with ERK1/2 and p38 controlling JNK. MAPK members regulated chemotaxis, but not the migratory speed, of DCs. CCR7 induced activation of PI3K/Akt; however, these enzymes did not regulate either chemotaxis or the speed of DCs. CCR7 also induced activation of the GTPase Rho, the tyrosine kinase Pyk2, and inactivation of cofilin. Pyk2 activation was independent of Gi and Src and was dependent on Rho. Interference with Rho or Pyk2 inhibited cofilin inactivation and the migratory speed of DCs, but did not affect chemotaxis. Interference with Rho/Pyk2/cofilin inhibited DC migratory speed even in the absence of chemokines, suggesting that this module controls the speed of DCs and that CCR7, by activating its components, induces an increase in migratory speed. Therefore, CCR7 activates two independent signaling modules, one involving Gi and a hierarchy of MAPK family members and another involving Rho/Pyk2/cofilin, which control, respectively, chemotaxis and the migratory speed of DCs. The use of independent signaling modules to control chemotaxis and speed can contribute to regulate the chemotactic effects of CCR7.

CCR7 was described initially as a potent leukocyte chemotactic receptor that was later shown to be responsible of directing the migration of dendritic cells (DCs) to the lymph nodes where these cells play an important role in the initiation of the immune response. Recently, a variety of reports have indicated that, apart from chemotaxis, CCR7 controls the cytoarchitecture, the rate of endocytosis, the survival, the migratory speed, and the maturation of the DCs. Some of these functions of CCR7 and additional ones also have been described in other cell types. Herein we discuss how this receptor may contribute to modulate the immune response by regulating different functions in DCs. Finally, we also suggest a possible mechanism whereby CCR7 may control its multiple tasks in these cells.

Acquisition of CCR7 expression is an important phenotype change during dendritic cell (DC) maturation that endows these cells with the capability to migrate to lymph nodes. We have analyzed the possible role of CCR7 on the regulation of the survival of DCs. Stimulation with CCR7 ligands CCL19 and CCL21 inhibits apoptotic hallmarks of serum-deprived DCs, including membrane phosphatidylserine exposure, loss of mitochondria membrane potential, increased membrane blebs, and nuclear changes. Both chemokines induced a rapid activation of phosphatidylinositol 3-kinase/Akt1 (PI3K/Akt1), with a prolonged and persistent activation of Akt1. Interference with PI3K, Gi, or G protein ␤␥ subunits abrogated the effects of the chemokines on Akt1 activation and on survival. In contrast, inhibition of extracellular signal-related kinase 1/2 (Erk1/2), p38, or c-Jun N-terminal kinase (JNK) was ineffective. Nuclear factor-B (NFB) was involved in the antiapoptotic effects of chemokines because inhibition of NFB blunted the effects of CCL19 and CCL21 on survival. Furthermore, chemokines induced down-regulation of the NFB inhibitor IB, an increase of NFB DNA-binding capability, and translocation of the NFB subunit p65 to the nucleus. In summary, in addition to its well-established role in chemotaxis, we show that CCR7 also induces antiapoptotic signaling in mature DCs. IntroductionApoptosis, or programmed cell death, is a physiologic process involved in the normal development and maintenance of tissue homeostasis. 1 The final stage of this process that leads to the demise of the cell is executed by proteases that degrade vital molecular components of the cell. 1 Hallmarks of cells undergoing apoptosis include disruption of mitochondria transmembrane potential, apparition of numerous blebs on the membrane, increased nuclear condensation, and increased appearance of phosphatidylserine (PS) in the outer leaflet of the cell membrane.Apoptosis is a programmed process that is regulated through a complex mechanism that involves multiple molecular intermediates. Surface receptors may inhibit apoptosis by relaying intracellular signals that either repress proapoptotic molecules and/or stimulate antiapoptotic ones. 1 Multiple pathways that inhibit apoptosis use as a common signaling intermediate phosphatidylinositol 3Ј-kinase (PI3K) and its downstream effector Akt1. 1-3 Akt1 phosphorylates and inhibits a variety of proapoptotic regulators and also regulates proteins that promote cell survival. [1][2][3] In this regard, it has been shown that Akt1 may activate IB kinase, which induces phosphorylation and subsequent degradation of IB, a molecule that binds and retains transcription factor nuclear factor-B (NFB) in the cytoplasm. 1-3 Upon IB degradation, NFB translocates to the nucleus and stimulates transcription from a variety of antiapoptotic genes. 2,4 Apart from PI3K/Akt1, in some cell settings, mitogen-activated protein kinase (MAPK) family members have also been shown to play an important role as regulators of apoptosis. [5][6][7] Dendritic ...