TRAIL is a tumor necrosis factor-related ligand that induces apoptosis upon binding to its death domaincontaining receptors, DR4 and DR5. Two additional TRAIL receptors, TRID/DcR1 and DcR2, lack functional death domains and function as decoy receptors for TRAIL. We have identified a fifth TRAIL receptor, namely osteoprotegerin (OPG), a secreted tumor necrosis factor receptor homologue that inhibits osteoclastogenesis and increases bone density in vivo. OPG-Fc binds TRAIL with an affinity of 3.0 nM, which is slightly weaker than the interaction of TRID-Fc or DR5-Fc with TRAIL. OPG inhibits TRAIL-induced apoptosis of Jurkat cells. Conversely, TRAIL blocks the anti-osteoclastogenic activity of OPG. These data suggest potential cross-regulatory mechanisms by OPG and TRAIL.

The early events in legume nodulation by Rhizobium spp. involve a conserved gene cluster known as the common nod region. A broad-host-range plasmid (pEA2-21) containing a Bradyrhizobium japonicum nodDABC-acZ translational fusion was constructed and used to monitor nod gene expression in response to soybean root extract. Two inducing compounds were isolated and identified. Analysis using ultraviolet absorption spectra, proton nuclear magnetic resonance, and mass spectrometry showed that the two inducers were 4',7-dihydroxyisoflavone (daidzein) and 4',5,7-trihydroxyisoflavone (genistein). Induction was also seen with some, but not all, of the flavonoid compounds that induce nod genes in fast-growing Rhizobium strains that nodulate clover, alfalfa, or peas. When pEA2-21 was introduced into Rhizobium trifohii, it was inducible by flavones but not by daidzein and genistein. In Rhizobium fredii, pEA2-21 was induced by isoflavones and flavones. Thus, the specificity of induction appears to be influenced by the host-strain genome.Members of the bacterial genus Rhizobium form symbiotic associations with leguminous plants that result in the formation of nitrogen-fixing root nodules. In three agronomically important Rhizobium/legume associations, R. trifolii/clover, R. meliloti/alfalfa, and R. leguminosarum/pea, important bacterial nodulation genes (1-4) and plant compounds that induce them (5-7) have been identified. In these associations flavones (5-7) or flavanones (7) have been found to induce the nodABC genes, as well as other nod genes involved in host specificity (1). Isoflavones have been found to inhibit the induction of nodABC in R. leguminosarum (7).The Bradyrhizobium japonicum/soybean symbiosis is of considerable agricultural importance. In contrast to Rhizobium spp., Bradyrhizobium species are slow-growing (8), nitrogen-fixation and nodulation genes are located on the chromosome (9) and not on plasmids (10)(11)(12), and less is known about the genetic requirements for nodulation (13)(14)(15). In particular, the compounds produced by the soybean host that interact with the common nod genes have not been characterized.In this study, a nodABC-lacZ translational fusion was used to monitor nod gene expression in B. japonicum in response to soybean root extract. Two major components from soybeans (Glycine max cv. Williams) were isolated that induced the expression of the nodABC-lacZ fusion when it was present in the soybean-nodulating bacteria B. japonicum and Rhizobium fredii, but not when it was present in R. trifolii. MATERIALS AND METHODSStrains and Plasmids. Standard procedures (16) were used for DNA manipulations. A HindIII fragment containing the nod region of B. japonicum USDA 123 was cloned in both orientations into the single HindIII site of plC19R (17). BamHI-Bgl II fragments containing the nod genes and flanking polylinker sequences were then cloned into the BamHI site of the broad-host-range vector pGD926 (18) resulting in pEA2-21 and pEA4-10 (Fig. 1) (19) agar and germinated for 3 days in the d...

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Eotaxin has been found to bind exclusively to a single chemokine receptor, CCR3. Using expression sequence tag screening of an activated monocyte library, a second chemokine has been identified; it was expressed and purified from a Drosophila cell culture system and appears to only activate CCR3. Eotaxin-2, MPIF-2, or CKbeta-6, is a human CC chemokine with low amino acid sequence identity to other chemokines. Eotaxin-2 promotes chemotaxis and Ca2+ mobilization in human eosinophils but not in neutrophils or monocytes. Cross-desensitization calcium mobilization experiments using purified eosinophils indicate that eotaxin and MCP-4, but not RANTES, MIP-1alpha, or MCP-3, can completely cross-desensitize the calcium response to eotaxin-2 on these cells, indicating that eotaxin-2 shares the same receptor used by eotaxin and MCP-4. Eotaxin-2 was the most potent eosinophil chemoattractant of all the chemokines tested. Eotaxin-2 also displaced 125I-eotaxin bound to the cloned CCR3 stably expressed in CHO cells (CHO-CCR3) and to freshly isolated human eosinophils with affinities similar to eotaxin and MCP-4. 125I-Eotaxin-2 binds with high affinity to eosinophils and both eotaxin and cold eotaxin-2 displace the ligand with equal affinity. Eotaxin and eotaxin-2 promote a Ca2+ transient in RBL-2H3 cells stably transfected with CCR3 (RBL-2H3-CCR3) and both ligands cross-desensitized the response of the other but not the response to LTD4. The data indicate that eotaxin-2 is a potent eosinophil chemotactic chemokine exerting its activity solely through the CCR3 receptor.

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