Activated insulin-specific CD8+ T cells (IS-CD8+ cells) home to the pancreas, destroy β cells, and cause rapid diabetes upon transfer into diabetes-prone NOD mice. Surprisingly, they also cause diabetes in mouse strains that are free of preexistent inflammation. Thus, we hypothesized that islet-specific homing may be in part dependent on IS-CD8+ cells' recognition of the cognate major histocompatibility complex (MHC)/peptide complexes presented by pancreatic endothelial cells, which acquire the antigen (insulin) from β cells. In fact, islet-specific homing was abrogated in mice that lack MHC class I expression, or presentation of the specific peptide, or have impaired insulin secretion. Moreover, we found that IS-CD8+ cells directly recognized pancreatic endothelial cells in islet organ cultures. Triggering of IS-CD8+ cells' T cell receptor (TCR) led to activation of integrins expressed by these cells. In addition, chemokines, particularly SLC (CCL21), were also required for IS-CD8+ cells' adhesion to endothelial monolayers and for successful homing in vivo. Thus, signaling through TCR and chemokine receptors work in concert to assure firm adhesion of T cells to the pancreatic endothelium. The antigen cross-presentation ability of endothelia may therefore contribute to the specificity of homing of activated T lymphocytes to the tissues where antigens are generated by other cell types.

Inhalation anthrax is a deadly disease for which there is currently no effective treatment. Bacillus anthracis lethal factor (LF) metalloproteinase is an integral component of the tripartite anthrax lethal toxin that is essential for the onset and progression of anthrax. We report here on a fragment-based approach that allowed us to develop inhibitors of LF. The small-molecule inhibitors we have designed, synthesized, and tested are highly potent and selective against LF in both in vitro tests and cell-based assays. These inhibitors do not affect the prototype human metalloproteinases that are structurally similar to LF. Initial in vivo evaluation of postexposure efficacy of our inhibitors combined with antibiotic ciprofloxican against B. anthracis resulted in significant protection. Our data strongly indicate that the scaffold of inhibitors we have identified is the foundation for the development of novel, safe, and effective emergency therapy of postexposure inhalation anthrax.

Pathogens or their toxins, including influenza virus, Pseudomonas, and anthrax toxins, require processing by host proprotein convertases (PCs) to enter host cells and to cause disease. Conversely, inhibiting PCs is likely to protect host cells from multiple furin-dependent, but otherwise unrelated, pathogens. To determine if this concept is correct, we designed specific nanomolar inhibitors of PCs modeled from the extended cleavage motif TPQRERRRKKR2GL of the avian influenza H5N1 hemagglutinin. We then confirmed the efficacy of the inhibitory peptides in vitro against the fluorescent peptide, anthrax protective antigen (PA83), and influenza hemagglutinin substrates and also in mice in vivo against two unrelated toxins, anthrax and Pseudomonas exotoxin. Peptides with Phe/Tyr at P1 were more selective for furin. Peptides with P1 Thr were potent against multiple PCs. Our strategy of basing the peptide sequence on a furin cleavage motif known for an avian flu virus shows the power of starting inhibitor design with a known substrate. Our results confirm that inhibiting furin-like PCs protects the host from the distinct furin-dependent infections and lay a foundation for novel, host cell-focused therapies against acute diseases.

IFN-γ is a cytokine with pleiotropic functions that participates in immune and autoimmune responses. The lack of IFN-γ is known to delay the development of autoimmune diabetes in nonobese diabetic (NOD) mice. Splenocytes from diabetic NOD and IFN-γ knockout (KO) NOD mice transfer diabetes into NOD recipients equally well. However, adoptive transfer of diabetogenic T cells from NOD mice into NOD.IFN-γ-KO or NOD mice lacking β-chain of IFN-γ receptor (NOD.IFN-γRβ-KO) appeared to be much less efficient. We found that IFN-γ influences the ability of diabetogenic cells to penetrate pancreatic islets. Tracing in vivo of insulin-specific CD8+ T cells has shown that homing of these cells to the islets of Langerhans was affected by the lack of IFN-γ. While adhesion of insulin-specific CD8+ cells to microvasculature was normal, the diapedesis was significantly impaired. This effect was reversible by treatment of the animals with rIFN-γ. Thus, IFN-γ may, among other effects, influence immune and autoimmune responses by supporting the homing of activated T cells.

Elevated expression of membrane type-1 matrix metalloproteinase (MT1-MMP) is closely associated with malignancies. There is a consensus among scientists that cell surface-associated MT1-MMP is a key player in pericellular proteolytic events. Now we have identified an intracellular, hitherto unknown, function of MT1-MMP. We demonstrated that MT1-MMP is trafficked along the tubulin cytoskeleton. A fraction of cellular MT1-MMP accumulates in the centrosomal compartment. MT1-MMP targets an integral centrosomal protein, pericentrin. Pericentrin is known to be essential to the normal functioning of centrosomes and to mitotic spindle formation. Expression of MT1-MMP stimulates mitotic spindle aberrations and aneuploidy in nonmalignant cells. Volumes of data indicate that chromosome instability is an early event of carcinogenesis. In agreement, the presence of MT1-MMP activity correlates with degraded pericentrin in tumor biopsies, whereas normal tissues exhibit intact pericentrin. We believe that our data show a novel proteolytic pathway to chromatin instability and elucidate the close association of MT1-MMP with malignant transformation. Matrix metalloproteinases (MMP(s))1 are a comprehensive family of zinc-enzymes that degrade the extracellular matrix and cell surface molecules (1). Understanding the function of these enzymes in carcinogenesis is critical for the design of anti-cancer pharmaceuticals (2). MT1-MMP is a prototypic member of the membrane-tethered MMP subfamily (3). A transmembrane domain and a cytoplasmic tail (CT) of MT1-MMP associate this abundant membrane-tethered protease with discrete regions of the plasma membrane and the intracellular milieu, respectively. Although MT1-MMP is present in normal tissues, its enhanced expression, unlike of any other of the 23 known human MMPs, is closely associated with aggressive, invasive malignancies (1, 3-5). MT1-MMP transgenic mice displayed mammary gland abnormalities and tumor promotion in mammary gland (6).MT1-MMP functions as one of the main mediators of proteolytic events on the cell surface, and it is directly involved in the pericellular proteolysis of the extracellular matrix, cell surface adhesion, and signaling receptors and in the activation pathway of soluble secretory MMPs (5, 7-9) Cell surface-associated MT1-MMP acts as a growth factor in malignant cells and assumes tumor growth control (4). The conditional expression of MT1-MMP can, by itself, confer tumorigenicity on nonmalignant epithelial cells and cause the formation of invasive tumors (10). MT1-MMP also plays an important role in normal development; MT1-MMP knock-out mice are dwarfs, and they die prematurely (8,11). A loss of the structurally similar primordial At2-MMP induces dwarfism in Arabidopsis plants (12). There is no extracellular matrix in plants, however, that is similar to the collagenous extracellular matrix of mammals. This datum alone is enough to suggest that the protease plays a role in certain functionally relevant intracellular events in addition to its role in pericellular...

BackgroundEctopic vascular calcification is a common condition associated with aging, atherosclerosis, diabetes, and/or chronic kidney disease. Smooth muscle cells are the best characterized source of osteogenic progenitors in the vasculature; however, recent studies suggest that cells of endothelial origin can also promote calcification. To test this, we sought to increase the osteogenic potential of endothelial cells by overexpressing tissue‐nonspecific alkaline phosphatase (TNAP), a key enzyme that regulates biomineralization, and to determine the pathophysiological effect of endothelial TNAP on vascular calcification and cardiovascular function.Methods and ResultsWe demonstrated previously that mice transgenic for ALPL (gene encoding human TNAP) develop severe arterial medial calcification and reduced viability when TNAP is overexpressed in smooth muscle cells. In this study, we expressed the ALPL transgene in endothelial cells following endothelial‐specific Tie2‐Cre recombination. Mice with endothelial TNAP overexpression survived well into adulthood and displayed generalized arterial calcification. Genes associated with osteochondrogenesis (Runx2, Bglap, Spp1, Opg, and Col2a1) were upregulated in the aortas of endothelial TNAP animals compared with controls. Lesions in coronary arteries of endothelial TNAP mice showed immunoreactivity to Runx2, osteocalcin, osteopontin, and collagen II as well as increased deposition of sialoproteins revealed by lectin staining. By 23 weeks of age, endothelial TNAP mice developed elevated blood pressure and compensatory left ventricular hypertrophy with preserved ejection fraction.ConclusionsThis study presented a novel genetic model demonstrating the osteogenic potential of TNAP‐positive endothelial cells in promoting pathophysiological vascular calcification.

Background Islet transplantation is limited by the need for chronic immunosuppression and the paucity of donor tissue. As new sources of human β-cells are developed (e.g., stem cell-derived tissue), transplanting them in a durable device could obviate the need for immunosuppression, while also protecting the patient from any risk of tumorigenicity. Here, we studied (1) the survival and function of encapsulated human β-cells and their progenitors and (2) the engraftment of encapsulated murine β-cells in allo- and autoimmune settings. Methods Human islets and human fetal pancreatic islet-like cell clusters were encapsulated in polytetrafluorethylene devices (TheraCyte) and transplanted into immunodeficient mice. Graft survival and function was measured by immunohistochemistry, circulating human C-peptide levels, and blood glucose levels. Bioluminescent imaging was used to monitor encapsulated neonatal murine islets. Results Encapsulated human islet-like cell clusters survived, replicated, and acquired a level of glucose responsive insulin secretion sufficient to ameliorate hyperglycemia in diabetic mice. Bioluminescent imaging of encapsulated murine neonatal islets revealed a dynamic process of cell death followed by regrowth, resulting in robust long-term allograft survival. Further, in the non-obese diabetic (NOD) mouse model of type I diabetes, encapsulated primary β-cells ameliorated diabetes without stimulating a detectable T-cell response. Conclusions We demonstrate for the first time that human β-cells function is compatible with encapsulation in a durable, immunoprotective device. Moreover, our study suggests that encapsulation of β-cells before terminal differentiation will be a successful approach for new cell-based therapies for diabetes, such as those derived from stem cells.

MT1-MMP is a key enzyme in cancer cell invasion and metastasis. The activity of cellular MT1-MMP is regulated by furin-like proprotein convertases, TIMPs, shedding, autoproteolysis, dimerization, exocytosis, endocytosis, and recycling. Our data demonstrate that, in addition to these already known mechanisms, MT1-MMP is regulated by O-glycosylation of its hinge region. Insignificant autolytic degradation is characteristic for naturally expressed, glycosylated, MT1-MMP. In turn, extensive autolytic degradation, which leads to the inactivation of the protease and the generation of its C-terminal membrane-tethered degraded species, is a feature of overexpressed MT1-MMP. We have determined that incomplete glycosylation stimulates extensive autocatalytic degradation and self-inactivation of MT1-MMP. Self-proteolysis commences during the secretory process of MT1-MMP through the cell compartment to the plasma membrane. The strongly negatively charged sialic acid is the most important functional moiety of the glycopart of MT1-MMP. We hypothesize that sialic acid of the O-glycosylation cassette restricts the access of the catalytic domain to the hinge region and to the autolytic cleavage site and protects MT1-MMP from autolysis. Overall, our results point out that there is a delicate balance between glycosylation and self-proteolysis of MT1-MMP in cancer cells and that when this balance is upset the catalytically potent MT1-MMP pool is self-proteolyzed.Membrane-tethered MT1-MMP, 2 the most abundant member of the membrane-type (MT) matrix metalloproteinase subfamily, is distinguished from soluble MMPs by a short transmembrane domain and a cytoplasmic tail (1, 2). MT1-MMP functions in cancer cells as an important mediator of proteolytic events on the cell surface (3, 4), and it is directly engaged in the cleavage of cell surface receptors and the pericellular proteolysis of the extracellular matrix components (5-7). MT1-MMP expression is associated with a variety of pathophysiological conditions and especially with cell locomotion, tumor growth, and metastasis (4, 5, 8 -11).MT1-MMP and related membrane-tethered MMPs are regulated, both as proteinases and as membrane proteins, at the transcriptional and post-transcriptional levels by multifaceted coordinated mechanisms (12-22). The trafficking and the internalization of MT1-MMP have been identified as two additional mechanisms that regulate its biological functions. Both clathrin-coated pits and caveolae are involved in the internalization of 19,[23][24][25][26][27][28].To exercise its proteolytic activity, MT1-MMP requires the proteolytic removal of its N-terminal prodomain sequence (29). Because the prodomain part of MT1-MMP has the furin-cleavage motif, furin and related proprotein convertases (PCs) are the physiological activators of latent MT1-MMP (13, 30 -32). Proteolytic processing by the PCs leads to the activation of the latent MT1-MMP zymogen, which occurs primarily in the trans-Golgi network during the secretory passage of MT1-MMP (30, 33). The levels of expressio...