Search

The local environment of neurosecretory cells contains the major components of the plasminogen activation system, including the plasminogen activators, tissue plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), as well as binding sites for t-PA, the receptor for u-PA (uPAR), and also the plasminogen activator inhibitor, PAI-1. Furthermore, these cells express specific binding sites for plasminogen, which is available in the circulation and in interstitial fluid. Colocalization of plasminogen and its activators on cell surfaces provides a mechanism for promoting local plasminogen activation. Plasmin is retained on the cell surface where it is protected from its inhibitor, α2-antiplasmin. In neurosecretory cells, localized plasmin activity provides amechanism for extracellular processing of secreted hormones. Neurotransmitter release fromcatecholaminergic cells is negatively regulated by cleavage products formed by plasmin-mediated proteolysis. Recently, we have identified a major plasminogen receptor, Plg-RKT. We have found that Plg-RKT is highly expressed in chromaffin cells of the adrenal medulla as well as in other catecholaminergic cells and tissues. Plg-RKT-dependent plasminogen activation plays a key role in regulating catecholaminergic neurosecretory cell function. [ABSTRACT FROM AUTHOR]

The local environment of neurosecretory cells contains the major components of the plasminogen activation system, including the plasminogen activators, tissue plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), as well as binding sites for t-PA, the receptor for u-PA (uPAR), and also the plasminogen activator inhibitor, PAI-1. Furthermore, these cells express specific binding sites for plasminogen, which is available in the circulation and in interstitial fluid. Colocalization of plasminogen and its activators on cell surfaces provides a mechanism for promoting local plasminogen activation. Plasmin is retained on the cell surface where it is protected from its inhibitor, α2-antiplasmin. In neurosecretory cells, localized plasmin activity provides amechanism for extracellular processing of secreted hormones. Neurotransmitter release fromcatecholaminergic cells is negatively regulated by cleavage products formed by plasmin-mediated proteolysis. Recently, we have identified a major plasminogen receptor, Plg-RKT. We have found that Plg-RKT is highly expressed in chromaffin cells of the adrenal medulla as well as in other catecholaminergic cells and tissues. Plg-RKT-dependent plasminogen activation plays a key role in regulating catecholaminergic neurosecretory cell function. [ABSTRACT FROM AUTHOR]

The orthopoxviruses ectromelia virus (ECTV) and vaccinia virus (VACV) express secreted gamma interferon binding proteins (IFN-γBPs) with homology to the ligand binding domains of the host's IFN- receptor (IFN-γR1). Homology between these proteins is limited to the extracellular portions of the IFN-γR1 and the first 200 amino acids of the IFN-γBPs. The remaining 60 amino acids at the C termini of the IFN-γBPs contain a single cysteine residue shown to be important in covalent dimerization of the secreted proteins. The function of the remaining C-terminal domain (CTD) has remained elusive, yet this region is conserved within all orthopoxvirus IFN-γBPs. Using a series of C-terminal deletion constructs, we have determined that the CTD is essential for IFN-γ binding despite having no predicted homology to the IFN-γR1. Truncation of the ECTV IFN-γBP by more than two amino acid residues results in a complete loss of binding activity for both murine IFN-γ and human IFN-γ (hIFN-γ), as measured by surface plasmon resonance (SPR) and bioassay. Equivalent truncation of the VACV IFN-γBP resulted in comparable loss of hIFN-γ binding activity by SPR. Full-length IFN-γBPs were observed to form higher-ordered structures larger than the previously reported dimers. Mutants that were unable to bind IFN-γ with high affinity in SPR experiments failed to assemble into these higher-ordered structures and migrated as dimers. We conclude that the unique CTD of orthopoxvirus IFN-γBPs is important for the assembly of covalent homodimers as well as the assembly of higher-ordered structures essential for IFN-γ binding. [ABSTRACT FROM AUTHOR]

Proteins of the plasminogen activation system are broadly expressed throughout the nervous system, and key roles for these proteins in neuronal function have been demonstrated. Recent reports have established that plasminogen is synthesized in neuroendocrine tissues, making this protein and the proteolytic activity of the product of its activation, plasmin, available at sites separated anatomically from circulating, hepatocyte-derived plasminogen. Results with plasminogen-deficient humans and mice suggest a role for plasminogen in neuritogenesis. To elucidate the role of the plasminogen activation system in these processes, the function of plasminogen during neuritogenesis and neurite outgrowth was studied. It is shown here that plasminogen participates in neuritogenesis, as plasmin inhibitors reduced both neurite outgrowth and neurite length in PC-12 cells. The addition of exogenous plasminogen enhanced neurite outgrowth and neurite length in both PC-12 cells and primary cortical neurons. The proteolytic activity of plasmin was required, since mutation of the catalytic serine residue completely abolished the stimulatory activity. Furthermore, mutation of the lysine binding site within kringle 5 of the plasminogen molecule also reduced the neuritogenic activity of plasminogen. Additionally, we demonstrate that plasminogen specifically bound to laminin-1, the interaction resulted in increased plasminogen activation by tissue-type plasminogen activator, and was dependent on a functional lysine binding site within plasminogen kringle 5. Moreover, during NGF-induced neuritogenesis, laminin-1 was degraded, and this cleavage was catalyzed by plasmin. This study provides the first direct evidence that plasminogen participates in neurite outgrowth and also suggests that laminin-1 degradation by plasmin contributes to the process of neuritogenesis. [ABSTRACT FROM AUTHOR]

Ectromelia virus (ECTV), a natural mouse pathogen and the causative agent of mousepox, is closely related to variola virus (VARV), which causes smallpox in humans. Mousepox is an excellent surrogate small-animal model for smallpox. Both ECTV and VARV encode a multitude of host response modifiers that target components of the immune system and that are thought to contribute to the high mortality rates associated with infection. Like VARV, ECTV encodes a protein homologous to the ectodomain of the host gamma interferon (IFN-γ) receptor 1. We generated an IFN-γ binding protein (IFN-γbp) deletion mutant of ECTV to study the role of viral IFN-γbp (vIFN-γbp) in host-virus interaction and also to elucidate the contribution of this molecule to the outcome of infection. Our data show that the absence of vIFN-γbp does not affect virus replication per se but does have a profound effect on virus replication and pathogenesis in mice. BALB/c mice, which are normally susceptible to infection with ECTV, were able to control replication of the mutant virus and survive infection. Absence of vIFN-γbp from ECTV allowed the generation of an effective host immune response that was otherwise diminished by this viral protein. Mice infected with a vIFN-γbp deletion mutant virus, designated ECTV-IFN-γbpδ, produced increased levels of IFN-γ and generated robust cell-mediated and antibody responses. Using several strains of mice that exhibit differential degrees of resistance to mousepox, we show that recovery or death from ECTV infection is determined by a balance between the host's ability to produce IFN-γ and the virus' ability to dampen its effects. [ABSTRACT FROM AUTHOR]