Functional processing of fertilin: evidence for a critical role of proteolysis in sperm maturation and activation.
(57/1953)
Fertilin is a sperm surface protein with an essential role in fertilization. It is required for the migration of spermatozoa through the oviduct, for binding to the zona pellucida, and for efficient binding to the egg plasma membrane. Fertilin consists of two subunits, fertilin alpha and beta, both of which belong to the metalloprotease-disintegrin protein family (ADAMs). Fertilin alpha and beta are made as larger precursors that are processed proteolytically at different stages of sperm maturation in the testis and epididymis. Fertilin alpha is processed first, most likely by a pro-protein convertase in the secretory pathway of testicular cells. Fertilin beta is processed later, while spermatozoa are in transit through the epididymis. The processing of fertilin beta in the epididymis correlates with the acquisition of fertilization competence in spermatozoa, exposes an epitope that has a role in sperm-egg interactions, and triggers the relocalization of fertilin from the whole sperm head to the posterior head. These findings indicate that the proteolytic processing of fertilin and perhaps also other sperm proteins plays an important role in sperm maturation and activation in the epididymis. Further evaluation of the functional significance of proteolysis for sperm maturation should lead to new and exciting insights into the mechanism of sperm maturation, and may also uncover the cause of certain types of male infertility. The identification of the responsible proteases could provide novel targets for contraceptive drugs. (+info)
A novel proteolytic cleavage involved in Notch signaling: the role of the disintegrin-metalloprotease TACE.
(58/1953)
The Notch1 receptor is presented at the cell membrane as a heterodimer after constitutive processing by a furin-like convertase. Ligand binding induces the proteolytic release of Notch intracellular domain by a gamma-secretase-like activity. This domain translocates to the nucleus and interacts with the DNA-binding protein CSL, resulting in transcriptional activation of target genes. Here we show that an additional processing event occurs in the extracellular part of the receptor, preceding cleavage by the gamma-secretase-like activity. Purification of the activity accounting for this cleavage in vitro shows that it is due to TACE (TNFalpha-converting enzyme), a member of the ADAM (a disintegrin and metalloprotease domain) family of metalloproteases. Furthermore, experiments carried out on TACE-/- bone marrow-derived monocytic precursor cells suggest that this metalloprotease plays a prominent role in the activation of the Notch pathway. (+info)
Molecular cloning and characterization of a human metalloprotease disintegrin--a novel marker for dendritic cell differentiation.
(59/1953)
The 1alpha,25-dihydroxyvitamin D(3) (1,25- [OH](2)VD(3)) modulates the differentiation of monocytic cell lines and monocytes (MOs) in vitro. Up to now several target genes of 1,25(OH)(2)VD(3) have been described in monocytic cell lines; however, little is known about target genes in primary MOs. With the Differential Display technique, we found a transcript up-regulated by 1,25(OH)(2)VD(3) in short-term cultured human blood MOs, which we called MADDAM (metalloprotease and disintegrin dendritic antigen marker; EMBL/GenBank/DDBJ accession no. Y13786). Northern blot analysis confirmed this result and revealed a signal of MADDAM messenger RNA (mRNA) at about 7.5 kilobases (kb). Long-term culture (more than 20 hours) of MOs during macrophage (MAC) differentiation led to a rapid and complete down-regulation of MADDAM expression. In contrast, MADDAM expression was maintained in MOs differentiated along the dendritic cell (DC) pathway and induced in CD34(+)-derived DCs. In addition, in situ hybridization revealed signals of MADDAM mRNA in follicles of human lymph nodes and MADDAM mRNA was detected in freshly isolated human blood-DCs by reverse transcription-polymerase chain reaction (RT-PCR). By means of a database search, we found that MADDAM is a member of the ADAM (a metalloprotease and disintegrin) family, the human homologue to murine meltrin-beta (ADAM 19). From these data, we conclude that MADDAM is an important marker for the differentiation and characterization of DCs and the distinction between MACs and DCs. (Blood. 2000;96:732-739) (+info)
TNF-Induced shedding of TNF receptors in human polymorphonuclear leukocytes: role of the 55-kDa TNF receptor and involvement of a membrane-bound and non-matrix metalloproteinase.
(60/1953)
A down-modulation of both the 55-kDa (TNF-R55) and the 75-kDa (TNF-R75) TNF receptors is observed in neutrophils exposed to a variety of stimuli. Proteolytic cleavage of the extracellular region of both receptors (shedding) and, with TNF, internalization of TNF-R55 and shedding of TNF-R75 are the proposed mechanisms. We have characterized the TNF-induced shedding of TNF receptors in neutrophils and determined the nature of the involved proteinase. Neutrophils exposed to TNF release both TNF receptors. A release of TNF receptors comparable to that observed with TNF was induced with TNF-R55-specific reagents (mAbs and a mutant of TNF) but not with the corresponding TNF-R75-specific reagents. A hydroxamic acid compound (KB8301) almost completely inhibited shedding of TNF-R55 and to a lesser degree shedding of TNF-R75. KB8301 also inhibited FMLP-induced shedding to a similar extent. Shedding was also inhibited by 1,10-phenanthroline, but this effect was considered nonspecific as the compound, at variance with KB8301, almost completely inhibited TNF and FMLP-induced PMN activation. Diisopropylfluorophosphate partially inhibited shedding of TNF-R75, suggesting the contribution of a serine proteinase to the release of this receptor. Shedding activity was not affected by matrix metalloproteinases inhibitors nor was it released in the supernatants of FMLP-stimulated neutrophils. These results suggest that TNF induces release of its receptors, that such a release is mediated via TNF-R55, and that a membrane-bound and non-matrix metalloproteinase is involved in the process. The possibility that ADAM-17, which we show to be expressed in neutrophils, might be the involved proteinase is discussed. (+info)
ADAMTS-1 cleaves a cartilage proteoglycan, aggrecan.
(61/1953)
A disintegrin-like and metalloproteinase with thrombospondin type I motifs-1 (ADAMTS-1) is an extracellular matrix-anchored metalloproteinase. In this study we have demonstrated that ADAMTS-1 is able to cleave a major cartilage proteoglycan, aggrecan. N-terminal sequencing analysis of the cleavage product revealed that ADAMTS-1 cleaves the Glu(1871)-Leu(1872) bond within the chondroitin sulfate attachment domain of aggrecan. In addition, deletional analysis demonstrated that the C-terminal spacer region of ADAMTS-1 is necessary to degrade aggrecan. These results suggest that ADAMTS-1 may be involved in the turnover of aggrecan in vivo. (+info)
Antibody from mice immunized with DNA encoding the carboxyl-disintegrin and cysteine-rich domain (JD9) of the haemorrhagic metalloprotease, Jararhagin, inhibits the main lethal component of viper venom.
(62/1953)
Envenoming by the Brazilian pit viper, Bothrops jararaca, induces extensive local and systemic haemorrhage in humans. The severe and occasionally lethal outcome of envenoming is prevented only by administration of antivenom which is conventionally prepared by hyperimmunization of large animals with an individual venom or a range of venoms. Since snake venoms typically consist of numerous molecules, only some of which are toxic, antivenoms are antigenically crude preparations whose therapeutic value would theoretically be enhanced by restricting antibody specificity to toxic venom molecules. We report here that high-titre IgG antibody from mice immunized by the GeneGun with DNA encoding the carboxy-terminal JD9 domain of Jararhagin, a haemorrhage-inducing metalloprotease in B. jararaca venom, extensively neutralized the main lethal component of B. jararaca venom. This is to our knowledge the first study to apply DNA-based methods to preparation of antivenom; it represents a novel approach with greater immunological specificity and fewer hazards than conventional systems of antivenom production. (+info)
Notch1 signaling promotes the maturation of CD4 and CD8 SP thymocytes.
(63/1953)
Notch proteins regulate many developmental processes. Notch1 is highly expressed on thymocytes, but its role in regulating their development is not known. We show that activation of Notch1 signaling in CD4+CD8+ double positive thymocytes promotes the maturation of both CD4+ and CD8+ single positive thymocytes and that this occurs in the absence of interactions between the T cell receptor and MHC molecules expressed on thymic epithelial cells. We have also identified several genes that are transcriptionally regulated by Notch1 in T cells and show that they are upregulated during maturation into both single positive lineages. These observations suggest that Notch1 signaling plays a role in promoting maturation into both the CD4 and CD8 T cell lineages. (+info)
RGD-independent binding of integrin alpha9beta1 to the ADAM-12 and -15 disintegrin domains mediates cell-cell interaction.
(64/1953)
ADAMs (a disintegrin and metalloproteases) mediate several important processes (e.g. tumor necrosis factor-alpha release, fertilization, and myoblast fusion). The ADAM disintegrin domains generally lack RGD motifs, and their receptors are virtually unknown. Here we show that integrin alpha(9)beta(1) specifically interacts with the recombinant ADAMs-12 and -15 disintegrin domains in an RGD-independent manner. We also show that interaction between ADAM-12 or -15 and alpha(9)beta(1) supports cell-cell interaction. Interestingly, the cation requirement and integrin activation status required for alpha(9)beta(1)/ADAM-mediated cell adhesion and cell-cell interaction is similar to those required for known integrin-extracellular matrix interaction. These results are quite different from recent reports that ADAM-2/alpha(6)beta(1) interaction during sperm/egg fusion requires an integrin activation status distinct from that for extracellular matrix interaction. These results suggest that alpha(9)beta(1) may be a major receptor for ADAMs that lack RGD motifs, and that, considering a wide distribution of ADAMs and alpha(9)beta(1), this interaction may be of potential biological and pathological significance. (+info)