Bone morphogenetic proteins (BMPs), including the fly homologue Decapentaplegic (DPP), are important regulators of early vertebrate and invertebrate dorsal-ventral development. An evolutionarily conserved BMP regulatory mechanism operates from fly to fish, frog and mouse to control the dorsal-ventral axis determination. Several secreted factors, including the BMP antagonist chordin/Short gastrulation (SOG), modulate the activity of BMPs. In Drosophila, Twisted gastrulation (TSG) is also involved in dorsal-ventral patterning, yet the mechanism of its function is unclear. Here we report the characterization of the vertebrate Tsg homologues. We show that Tsg can block BMP function in Xenopus embryonic explants and inhibits several ventral markers in whole-frog embryos. Tsg binds directly to BMPs and forms a ternary complex with chordin and BMPs. Coexpression of Tsg with chordin leads to a more efficient inhibition of the BMP activity in ectodermal explants. Unlike other known BMP antagonists, however, Tsg also reduces several anterior markers at late developmental stages. Our data suggest that Tsg can function as a BMP inhibitor in Xenopus; furthermore, Tsg may have additional functions during frog embryogenesis.

TheIt is well established that ligand binding and cell-surface clustering of integrins can lead to the assembly of large multicomponent intracellular signaling complexes (1-4). More recently, integrins have also been found to associate with other cell-surface molecules. For example, the CD47/IAP molecule associates with integrin ␣ V ␤ 3 (5, 6), and glycosylphosphatidylinositol-linked receptors such as CD87/uPAR, CD16b/ Fc␥RIIIB, and CD14 show functionally relevant interactions with ␤ 1 (7) and ␤ 2 (8, 9) integrins. In addition, proteins from the tetraspan or transmembrane-4 superfamily (TM4SF), 1 including CD9, CD53, CD63, CD81, and CD82, interact with several integrins, including ␣

Transmembrane-4 superfamily (TM4SF) proteins form complexes with integrins and other cell-surface proteins. To further characterize the major proteins present in a typical TM4SF protein complex, we raised monoclonal antibodies against proteins co-immunoprecipitated with CD81 from MDA-MB-435 breast cancer cells. Only two types of cell-surface proteins were recognized by our 35 selected antibodies. These included an integrin (alpha6beta1) and three different TM4SF proteins (CD9, CD63, and NAG-2). The protein NAG-2 (novel antigen-2) is a previously unknown 30-kDa cell-surface protein. Using an expression cloning protocol, cDNA encoding NAG-2 was isolated. When aligned with other TM4SF proteins, the deduced amino acid sequence of NAG-2 showed most identity (34%) to CD53. Flow cytometry, Northern blotting, and immunohistochemistry showed that NAG-2 is widely present in multiple tissues and cell types but is absent from brain, lymphoid cells, and platelets. Within various tissues, strongest staining was seen on fibroblasts, endothelial cells, follicular dendritic cells, and mesothelial cells. In nonstringent detergent, NAG-2 protein was co-immunoprecipitated with other TM4SF members (CD9 and CD81) and integrins (alpha3beta1 and alpha6beta1). Also, two-color immunofluorescence showed that NAG-2 was co-localized with CD81 on the surface of spread HT1080 cells. These results confirm the presence of NAG-2 in specific TM4SF.TM4SF and TM4SF-integrin complexes.

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The engagement of antigen receptor can initiate apoptosis of T lymphocytes through the induced expression of Fas ligand (FasL). Forskolin, an activator of the cAMP/PKA pathway, results in antagonism of Fas‐dependent, activation‐induced cell death (AICD) by suppressed expression of the FasL. We report that forskolin‐mediated induction of inducible cAMP early repressor (ICER) correlates with transcriptional attenuation of FasL expression in the AICD model 2B4 T cell hybridoma. ICER is inducible in human peripheral blood CD3+ T cells, but in CD19+ B cells, its induction is less responsive to forskolin treatment. Increased expression of ICER correlates with decreased FasL expression in both T and NK cells. ICER binds specifically to the proximal DNA binding siteof the nuclear factor of activated T cells (NFAT) in the FasL promoter and in the presence of the minimal NFAT DNA‐binding domain, the proximal NFAT motif allows ICER and NFAT to form an NFAT/ICER ternary complex in vitro. Moreover, in the activated 2B4 T cell hybridoma, the proximal NFAT motif participates in the down‐regulation of the FasL promoter mediated by ICER. These findings provide further insight into the mechanism involved in cAMP‐mediated transcriptional attenuation of FasL expression in T and NK lymphocytes.

Here, we have utilized six new anti-human beta 5 monoclonal antibodies to perform a detailed investigation of the structure, function and distribution of beta 5 integrins. Monoclonal anti-beta 5 specificity was confirmed by reactivity with beta 5-transfected CHO cells, by direct binding to the beta 5 subunit (immunoblotting), and by immunodepletion experiments using polyclonal anti-beta 5 serum. The beta 5 subunit was predominantly associated with the alpha v subunit, although on some cell lines, the level of beta 5 exceeded that of alpha v for unknown reasons. Cell adhesion studies showed that the adhesive function of beta 5 could be stimulated, inhibited or unaltered by different anti-beta 5 monoclonal antibodies. The beta 5 subunit was involved in adhesion to both vitronectin and fibronectin and, at least for K562 cells, fibronectin appeared to be the preferred ligand. Flow-cytometry studies showed that the beta 5 subunit was expressed at moderate to high levels on all adherent cell lines examined, was absent from all lymphoid cell lines, and was only weakly expressed on myeloid cell lines. Staining of thymic sections showed the distribution of beta 5 on blood vessels, Hassal's corpuscles, cortical and medullary stromal cells, and basement membranes. Skin sections showed beta 5 on the basal layer of the epidermis and on some dermal blood vessel walls, and kidney sections showed staining of glomerular regions, juxta glomerular apparatus, proximal convoluted tubules and collecting tubules, and at least one anti-beta 5 antibody also stained epithelial cells of proximal tubules.

Depending on the nature of the costimulation of T lymphocytes, expression of regulatory cytokines and chemokines is either susceptibleor resistant to cyclic AMP (cAMP)-mediated inhibition. Our data showthat cAMP-mediated inhibition of endogenously expressed cytokines, which is characteristic for T helper (Th) 1- and Th 2-like phenotypes, correlates with the induction of a potent transcriptional repressor, inducible cAMP early repressor (ICER), in both subsets of T cellsactivated under conditions of suboptimal interleukin-2 (IL-2)expression. Importantly, Th-specific expression of certain chemokinesis also susceptible to cAMP-mediated transcriptional attenuation. Todetermine whether ICER per se, rather than forskolin-mediated elevationof intracellular cAMP, is responsible for the observed inhibitoryeffect, we generated transgenic mice expressing ICER under the controlof a lymphocyte-specific lck promoter. On stimulation, transgenic thymocytes overexpressing ICER exhibited reduced levels of IL-2 and interferon (IFN)-γ and failed to express the macrophageinflammatory protein (MIP)-1α and MIP-1β genes. Splenic T cellsfrom ICER-transgenic mice showed a defect in proliferation and lacked amixed lymphocyte reaction response, implying that ICER-mediatedinhibition of cytokine and chemokine expression might play an importantrole in T-cell inactivation.

The M. tuberculosis rpoA gene, encoding the a subunit of RNA polymerase, was isolated by a polymerase chain reaction-based strategy using primers directed against regions of a that are highly conserved among Gram-positive and Gram-negative bacteria. The amplified DNA was utilized as a hybridization probe to recover the entire rpoA gene from a cosmid library of genomic DNA from virulent M. tuberculosis strain H37Rv. Nucleotide sequencing indicated that the 1044 bp M. tuberculosis rpoA open reading frame (ORF) encodes a protein of 347 amino acids which shows significant structural similarity to the a subunits of diverse bacterial species. Recombinant M. tuberculosis a subunit was overproduced in soluble form in E. coli as a hexahistidine-tagged fusion protein and purified to homogeneity by affinity chromatography.