Calcium mobilization and phosphoinositide turnover as measure of chemokine receptor function in lymphocytes

Pharmacological and signaling analysis of human chemokine receptor CCR-7 stably expressed in HEK-293 cells: high-affinity binding of recombinant ligands MIP-3beta and SLC stimulates multiple signaling cascades

The chemokine receptor CCR-7 is expressed in T, NK, and dendritic cells in a time-ordered and stimulus-dependent manner. Thorough analyses of the pharmacological profiles of the recombinant ligands for CCR-7, MIP-3beta/ELC/CK-beta 11, and SLC/Exodus-2/TCA4/6C-kine, using CCR-7-expressing HEK-293E transfectants determine that ligands both bind with a K(d) in the 100 pM range-10- to 100-fold greater affinities than published K(d) values. High-affinity binding of each ligand is associated with rapid mobilization of intracellular calcium and cell migration as predicted for chemokine GPCRs, and in keeping with more recent evidence, robust activation of mitogen-activated protein kinase (MAPK).

Endothelins activate Ca(2+)-gated K(+) channels via endothelin B receptors in CD-1 mouse erythrocytes

Cell dehydration mediated by Ca(2+)-activated K(+) channels plays an important role in the pathogenesis of sickle cell disease. CD-1 mouse erythrocytes possess a Ca(2+)-activated K(+) channel (Gardos channel) with maximal velocity (V(max)) of 0.154 +/- 0.02 mmol. l cells(-1). min(-1) and an affinity constant (K(0.5)) for Ca(2+) of 286 +/- 83 nM in the presence of A-23187. Cells pretreated with 500 nM endothelin-1 (ET-1) increased their V(max) by 88 +/- 9% (n = 8) and decreased their K(0.5) for Ca(2+) to 139 +/- 63 nM (P < 0.05; n = 4). Activation of the Gardos channel resulted in an EC(50) of 75 +/- 20 nM for ET-1 and 374 +/- 97 nM for ET-3. Analysis of the affinity of unlabeled ET-1 for its receptor showed two classes of binding sites with apparent dissociation constants of 167 +/- 51 and 785 +/- 143 nM and with capacity of binding sites of 298 +/- 38 and 1,568 +/- 211 sites/cell, respectively. The Gardos channel was activated by the endothelin B (ET(B)) receptor agonist IRL 1620 and inhibited by BQ-788, demonstrating the involvement of ET(B) receptors. Calphostin C inhibited 73% of ET-1-induced Gardos activation and 84% of the ET-1-induced membrane protein kinase C activity. Thus endothelins regulate erythrocyte Gardos channels via ET(B) receptors and a calphostin-sensitive mechanism.

Azodicarbonamide inhibits T-cell responses in vitro and in vivo

Azodicarbonamide was recently identified as a new anti-HIV agent that targets the zinc finger domains of the HIV-1 NCp7 nucleocapsid protein. Here, we demonstrate that azodicarbonamide inhibits in a dose-dependent manner the responses of purified human CD4+ T lymphocytes stimulated either by monoclonal antibodies against CD3 and CD28 or by allogeneic dendritic cells. These suppressive effects involve a direct action on the calcium mobilization machinery, as azodicarbonamide strongly inhibited the calcium influx induced either by antibodies against CD3 and CD28 or the chemokine RANTES, as well as by thapsigargin, an activator of depletion-activated calcium channels. In vivo, administration of azodicarbonamide into mice blunted their response to polyclonal T-cell activation induced by the injection of monoclonal antibody against CD3 and resulted in delayed rejection of skin allografts. In addition to its anti-HIV properties, azodicarbonamide is a new immunosuppressive agent that might have therapeutic applications in T cell-mediated inflammatory disorders.