Towards antigen-specific Tregs for type 1 diabetes: Construction and functional assessment of pancreatic endocrine marker, HPi2-based chimeric antigen receptor.

Type 1 Diabetes (T1D) is an autoimmune disease marked by direct elimination of insulin-producing ß cells by autoreactive T effectors. Recent T1D clinical trials utilizing autologous Tregs transfers to restore immune balance and improve disease has prompted us to design a novel Tregs-based antigen-specific T1D immunotherapy. We engineered a Chimeric Antigen Receptor (CAR) expressing a single-chain Fv recognizing the human pancreatic endocrine marker, HPi2. Human T cells, transduced with the resultant HPi2-CAR, proliferated and amplified Granzyme B accumulation when co-cultured with human, but not mouse ß cells. Furthermore, following exposure of HPi2-CAR transduced cells to islets, CD8+ lymphocytes demonstrated enhanced CD107a (LAMP-1) expression, while CD4+ cells produced increased levels of IL-2. HPi2-CAR Tregs failed to maintain expansion due to a persistent tonic signaling from the CAR engagement to unexpectantly HPi2 antigen present on Tregs. Overall, we show lack of functionality of HPi2-CAR and highlight the importance of careful selection of CAR recognition driver for the sustainable activity and expandability of engineered T cells.

Overexpression of tissue-nonspecific alkaline phosphatase (TNAP) in endothelial cells accelerates coronary artery disease in a mouse model of familial hypercholesterolemia.

OBJECTIVE: Overexpression of tissue-nonspecific alkaline phosphatase (TNAP) in endothelium leads to arterial calcification in mice. The purpose of this study was to examine the effect of elevated endothelial TNAP on coronary atherosclerosis. In addition, we aimed to examine endogenous TNAP activity in human myocardium. APPROACH AND RESULTS: A vascular pattern of TNAP activity was observed in human non-failing, ischemic, and idiopathic dilated hearts (5 per group); no differences were noted between groups in this study. Endothelial overexpression of TNAP was achieved in mice harboring a homozygous recessive mutation in the low density lipoprotein receptor (whc allele) utilizing a Tie2-cre recombinase (WHC-eTNAP mice). WHC-eTNAP developed significant coronary artery calcification at baseline compared WHC controls (4312 vs 0µm2 alizarin red area, p<0.001). Eight weeks after induction of atherosclerosis, lipid deposition in the coronary arteries of WHC-eTNAP was increased compared to WHC controls (121633 vs 9330µm2 oil red O area, p<0.05). Coronary lesions in WHC-eTNAP mice exhibited intimal thickening, calcifications, foam cells, and necrotic cores. This was accompanied by the reduction in body weight and left ventricular ejection fraction (19.5 vs. 23.6g, p<0.01; 35% vs. 47%, p<0.05). In a placebo-controlled experiment under atherogenic conditions, pharmacological inhibition of TNAP in WHC-eTNAP mice by a specific inhibitor SBI-425 (30mg*kg-1*d-1, for 5 weeks) reduced coronary calcium (78838 vs.144622µm2) and lipids (30754 vs. 77317µm2); improved body weight (22.4 vs.18.8g) and ejection fraction (59 vs. 47%). The effects of SBI-425 were significant in the direct comparisons with placebo but disappeared after TNAP-negative placebo-treated group was included in the models as healthy controls. CONCLUSIONS: Endogenous TNAP activity is present in human cardiac tissues. TNAP overexpression in vascular endothelium in mice leads to an unusual course of coronary atherosclerosis, in which calcification precedes lipid deposition. The prevalence and significance of this mechanism in human atherosclerosis requires further investigations.

Transgenic Overexpression of Tissue-Nonspecific Alkaline Phosphatase (TNAP) in Vascular Endothelium Results in Generalized Arterial Calcification.

BACKGROUND: Ectopic 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 RESULTS: We 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. CONCLUSIONS: This study presented a novel genetic model demonstrating the osteogenic potential of TNAP-positive endothelial cells in promoting pathophysiological vascular calcification.

Engineering a leucine zipper-TRAIL homotrimer with improved cytotoxicity in tumor cells.

Successful cancer therapies aim to induce selective apoptosis in neoplastic cells. The current suboptimal efficiency and selectivity drugs have therapeutic limitations and induce concomitant side effects. Recently, novel cancer therapies based on the use of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) have emerged. TRAIL, a key component of the natural antitumor immune response, selectively kills many tumor cell types. Earlier studies with recombinant TRAIL, however, revealed its many shortcomings including a short half-life, off-target toxicity, and existence of TRAIL-resistant tumor cells. We improved the efficacy of recombinant TRAIL by redesigning its structure and the expression and purification procedures. The result is a highly stable leucine zipper (LZ)-TRAIL chimera that is simple to produce and purify. This chimera functions as a trimer in a manner that is similar to natural TRAIL. The formulation of the recombinant LZ-TRAIL we have developed has displayed high specific activity in both cell-based assays in vitro and animal tests in vivo. Our results have shown that the half-life of LZ-TRAIL is improved and now exceeds 1 h in mice compared with a half-life of only minutes reported earlier for recombinant TRAIL. We have concluded that our LZ-TRAIL construct will serve as a foundation for a new generation of fully human LZ-TRAIL proteins suitable for use in preclinical and clinical studies and for effective combination therapies to overcome tumor resistance to TRAIL.

Human beta-cell precursors mature into functional insulin-producing cells in an immunoisolation device: implications for diabetes cell therapies.

BACKGROUND: Islet transplantation is limited by the need for chronic immunosuppression and the paucity of donor tissue. As new sources of human beta-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 beta-cells and their progenitors and (2) the engraftment of encapsulated murine beta-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 beta-cells ameliorated diabetes without stimulating a detectable T-cell response. CONCLUSIONS: We demonstrate for the first time that human beta-cells function is compatible with encapsulation in a durable, immunoprotective device. Moreover, our study suggests that encapsulation of beta-cells before terminal differentiation will be a successful approach for new cell-based therapies for diabetes, such as those derived from stem cells.

Matrix metalloproteinases, T cell homing and beta-cell mass in type 1 diabetes.

The pathogenesis of type 1 diabetes begins with the activation of autoimmune T killer cells and is followed by their homing into the pancreatic islets. After penetrating the pancreatic islets, T cells directly contact and destroy insulin-producing beta cells. This review provides an overview of the dynamic interactions which link T cell membrane type-1 matrix metalloproteinase (MT1-MMP) and the signaling adhesion CD44 receptor with T cell transendothelial migration and the subsequent homing of the transmigrated cells to the pancreatic islets. MT1-MMP regulates the functionality of CD44 in diabetogenic T cells. By regulating the functionality of T cell CD44, MT1-MMP mediates the transition of T cell adhesion to endothelial cells to the transendothelial migration of T cells, thus, controlling the rate at which T cells home into the pancreatic islets. As a result, the T cell MT1-MMP-CD44 axis controls the severity of the disease. Inhibition of MT1-MMP proteolysis of CD44 using highly specific and potent synthetic inhibitors, which have been clinically tested in cancer patients, reduces the rate of transendothelial migration and the homing of T cells. Result is a decrease in the net diabetogenic efficiency of T cells and a restoration of beta cell mass and insulin production in NOD mice. The latter is a reliable and widely used model of type I diabetes in humans. Overall, existing experimental evidence suggests that there is a sound mechanistic rationale for clinical trials of the inhibitors of T cell MT1-MMP in human type 1 diabetes patients.

Matrix metalloproteinase proteolysis of the myelin basic protein isoforms is a source of immunogenic peptides in autoimmune multiple sclerosis.

BACKGROUND: Matrix metalloproteinases (MMPs) play a significant role in the fragmentation of myelin basic protein (MBP) and demyelination leading to autoimmune multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). The classic MBP isoforms are predominantly expressed in the oligodendrocytes of the CNS. The splice variants of the single MBP gene (Golli-MBP BG21 and J37) are widely expressed in the neurons and also in the immune cells. The relative contribution of the individual MMPs to the MBP cleavage is not known. METHODOLOGY/PRINCIPAL FINDINGS: To elucidate which MMP plays the primary role in cleaving MBP, we determined the efficiency of MMP-2, MMP-8, MMP-9, MMP-10, MMP-12, MT1-MMP, MT2-MMP, MT3-MMP, MT4-MMP, MT5-MMP and MT6-MMP in the cleavage of the MBP, BG21 and J37 isoforms in the in vitro cleavage reactions followed by mass-spectroscopy analysis of the cleavage fragments. As a result, we identified the MMP cleavage sites and the sequence of the resulting fragments. We determined that MBP, BG21 and J37 are highly sensitive to redundant MMP proteolysis. MT6-MMP (initially called leukolysin), however, was superior over all of the other MMPs in cleaving the MBP isoforms. Using the mixed lymphocyte culture assay, we demonstrated that MT6-MMP proteolysis of the MBP isoforms readily generated, with a near quantitative yield, the immunogenic N-terminal 1-15 MBP peptide. This peptide selectively stimulated the proliferation of the PGPR7.5 T cell clone isolated from mice with EAE and specific for the 1-15 MBP fragment presented in the MHC H-2(U) context. CONCLUSIONS/SIGNIFICANCE: In sum, our biochemical observations led us to hypothesize that MT6-MMP, which is activated by furin and associated with the lipid rafts, plays an important role in MS pathology and that MT6-MMP is a novel and promising drug target in MS especially when compared with other individual MMPs.

Molecular signature of MT1-MMP: transactivation of the downstream universal gene network in cancer.

Invasion-promoting MT1-MMP is directly linked to tumorigenesis and metastasis. Our studies led us to identify those genes, the expression of which is universally linked to MT1-MMP in multiple tumor types. Genome-wide expression profiling of MT1-MMP-overexpressing versus MT1-MMP-silenced cancer cells and a further data mining analysis of the preexisting expression database of 190 human tumors of 14 cancer types led us to identify 11 genes, the expression of which correlated firmly and universally with that of MT1-MMP (P < 0.00001). These genes included regulators of energy metabolism (NNT), trafficking and membrane fusion (SLCO2A1 and ANXA7), signaling and transcription (NR3C1, JAG1, PI3K delta, and CK2 alpha), chromatin rearrangement (SMARCA1), cell division (STK38/NDR1), apoptosis (DAPK1), and mRNA splicing (SNRPB2). Our subsequent extensive analysis of cultured cells, tumor xenografts, and cancer patient biopsies supported our data mining. Our results suggest that transcriptional reprogramming of the specific downstream genes, which themselves are associated with tumorigenesis, represents a distinctive "molecular signature" of the proteolytically active MT1-MMP. We suggest that the transactivation activity of MT1-MMP contributes to the promigratory cell phenotype, which is induced by this tumorigenic proteinase. The activated downstream gene network then begins functioning in unison with MT1-MMP to rework the signaling, transport, cell division, energy metabolism, and other critical cell functions and to commit the cell to migration, invasion, and, consequently, tumorigenesis.

Targeting host cell furin proprotein convertases as a therapeutic strategy against bacterial toxins and viral pathogens.

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 TPQRERRRKKR downward arrowGL 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.

Defining the roles of T cell membrane proteinase and CD44 in type 1 diabetes.

Membrane type-1 matrix metalloproteinase (MT1-MMP) shedding of the signaling and adhesion CD44 receptor plays a significant role in stimulating cancer cells locomotion. Similarly, and unexpectedly, MT1-MMP-dependent shedding of CD44 plays an equally significant role in regulating the adhesion to the pancreatic vasculature and also in the concomitant transendothelial migration and intra-islet homing of the diabetogenic, cytotoxic, T cells. Inactivation of the T cell MT1-MMP functionality by clinically tested, synthetic inhibitors leads to an extended immobilization of the T killer cells on the pancreatic vasculature and, subsequently, to immunosuppression because of the cessation of the T cell transmigration and homing. Injections of insulin jointly with an MT1-MMP inhibitor stimulated the regeneration of functional, insulin-producing, beta-cells in acutely diseased non-obese diabetic (NOD) mice. After insulin injections were suspended and inhibitor injections continued, diabetic NOD mice maintained mild hyperglycemia and did not require further insulin injections for survival. Overall, these data provide a substantive mechanistic rationale for clinical trials of the inhibitors of MT1-MMP in human type 1 diabetes.

Mechanistic insights into targeting T cell membrane proteinase to promote islet beta-cell rejuvenation in type 1 diabetes.

It has been well established that invasion-promoting membrane type-1 matrix metalloproteinase (MT1-MMP), a multifunctional membrane-tethered enzyme, functions in cancer cells as a mediator of pericellular proteolysis and directly cleaves several cell surface receptors, including CD44. In this report, we confirm that adhesion of diabetogenic T cells promotes the activation of endogenous MT1-MMP. Activated protease then cleaves CD44 in adherent T cells. We have validated that the T cell CD44 receptor is critical for the adhesion of diabetogenic insulin-specific, CD8-positive, K(d)-restricted cells to the matrix as well as for the subsequent transmigration of the adherent T cells through the endothelium and homing of the transmigrated T cells into the pancreatic islets. We have determined that the inhibition of MT1-MMP by low dosages of AG3340 (a subnanomolar range hydroxamate inhibitor of MMPs that has been widely tested in cancer patients) inhibited both T cell MT1-MMP activity and MT1-MMP-dependent shedding of CD44, immobilized T cells on the endothelium, repressed the homing of diabetogenic T cells into the pancreatic islets, reduced insulitis and mononuclear cell infiltration, and promoted either the recovery or the rejuvenation of the functional insulin-producing beta cells in diabetic NOD mice with freshly developed type I diabetes (IDDM). We believe our data constitute a mechanistic and substantive rationale for clinical trials of selected MT1-MMP inhibitors in the therapy of IDDM in humans.

Interference with the complement system by tumor cell membrane type-1 matrix metalloproteinase plays a significant role in promoting metastasis in mice.

Neoplasms have developed strategies to protect themselves against the complement-mediated host immunity. Invasion- and metastasis-promoting membrane type-1 (MT1) matrix metalloproteinase (MMP) is strongly associated with many metastatic cancer types. The relative importance of the individual functions of MT1-MMP in metastasis was, however, unknown. We have now determined that the expression of murine MT1-MMP in murine melanoma B16F1 cells strongly increased the number of metastatic loci in the lungs of syngeneic C57BL/6 mice. In contrast, MT1-MMP did not affect the number of metastatic loci in complement-deficient C57BL/6-C3-/- mice. Our results indicated, for the first time, that the anticomplement activity of MT1-MMP played a significant role in promoting metastasis in vivo and determined the relative importance of the anticomplement activity in the total metastatic effect of this multifunctional proteolytic enzyme. We believe that our results shed additional light on the functions of MT1-MMP in cancer and clearly make this protease a promising drug target in metastatic malignancies.

O-glycosylation regulates autolysis of cellular membrane type-1 matrix metalloproteinase (MT1-MMP).

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.

Matrix metalloproteinase 26 proteolysis of the NH2-terminal domain of the estrogen receptor beta correlates with the survival of breast cancer patients.

Estrogens have many cellular functions, including their interactions with estrogen receptors alpha and beta (ERalpha and ERbeta). Earlier, we determined that the estrogen-ER complex stimulates the transcriptional activity of the matrix metalloproteinase 26 (MMP-26) gene promoter. We then determined that ERbeta is susceptible to MMP-26 proteolysis whereas ERalpha is resistant to the protease. MMP-26 targets the NH(2)-terminal region of ERbeta coding for the divergent NH(2)-terminal A/B domain that is responsible for the ligand-independent transactivation function. As a result, MMP-26 proteolysis generates the COOH-terminal fragments of ERbeta. Immunohistochemical analysis of tissue microarrays derived from 121 cancer patients corroborated these data and revealed an inverse correlation between the ERalpha-dependent expression of MMP-26 and the levels of the intact ERbeta in breast carcinomas. MMP-26 is not expressed in normal mammary epithelium. The levels of MMP-26 are strongly up-regulated in ductal carcinoma in situ (DCIS). In the course of further disease progression through stages I to III, the expression of MMP-26 decreases. In contrast to many tumor-promoting MMPs, the expression of MMP-26 in DCIS correlated with a longer patient survival. Our data suggest the existence of an MMP-26-mediated intracellular pathway that targets ERbeta and that MMP-26, a novel and valuable cancer marker, contributes favorably to the survival of the ERalpha/beta-positive cohort of breast cancer patients.

Inhibition of membrane type-1 matrix metalloproteinase by cancer drugs interferes with the homing of diabetogenic T cells into the pancreas.

We have discovered that clinically tested inhibitors of matrix metalloproteinases can control the functional activity of T cell membrane type-1 matrix metalloproteinase (MT1-MMP) and the onset of disease in a rodent model of type 1 diabetes in non-obese diabetic mice. We determined that MT1-MMP proteolysis of the T cell surface CD44 adhesion receptor affects the homing of T cells into the pancreas. We also determined that both the induction of the intrinsic T cell MT1-MMP activity and the shedding of cellular CD44 follow the adhesion of insulin-specific, CD8-positive, Kd-restricted T cells to the matrix. Conversely, inhibition of these events by AG3340 (a potent hydroxamate inhibitor that was widely used in clinical trials in cancer patents) impedes the transmigration of diabetogenic T cells into the pancreas and protects non-obese diabetic mice from diabetes onset. Overall, our studies have divulged a previously unknown function of MT1-MMP and identified a promising novel drug target in type I diabetes.

Membrane type-1 matrix metalloproteinase (MT1-MMP) exhibits an important intracellular cleavage function and causes chromosome instability.

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 non-malignant 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 metalloproteinase-26 is associated with estrogen-dependent malignancies and targets alpha1-antitrypsin serpin.

Proteases exert control over cell behavior and affect many biological processes by making proteolytic modification of regulatory proteins. The purpose of this paper is to describe novel, important functions of matrix metalloproteinase (MMP)-26. alpha1-Antitrypsin (AAT) is a serpin, the primary function of which is to regulate the activity of neutrophil/leukocyte elastase. Insufficient antiprotease activity because of AAT deficiency in the lungs is a contributing factor to early-onset emphysema. We recently discovered that AAT is efficiently cleaved by a novel metalloproteinase, MMP-26, which exhibits an unconventional PH(81)CGVPD Cys switch motif and is autocatalytically activated in cells and tissues. An elevated expression of MMP-26 in macrophages and polymorphonuclear leukocytes supports the functional role of MMP-26 in the AAT cleavage and inflammation. We have demonstrated a direct functional link of MMP-26 expression with an estrogen dependency and confirmed the presence of the estrogen-response element in the MMP-26 promoter. Immunostaining of tumor cell lines and biopsy specimen microarrays confirmed the existence of the inverse correlations of MMP-26 and AAT in cells/tissues. An expression of MMP-26 in the estrogen-dependent neoplasms is likely to contribute to the inactivation of AAT, to the follow-up liberation of the Ser protease activity, and because of these biochemical events, to promote matrix destruction and malignant progression. In summary, we hypothesize that MMP-26, by cleaving and inactivating the AAT serpin, operates as a unique functional link that regulates a coordinated interplay between Ser and metalloproteinases in estrogen-dependent neoplasms.

Cellular membrane type-1 matrix metalloproteinase (MT1-MMP) cleaves C3b, an essential component of the complement system.

Neoplasms have developed numerous strategies to protect themselves against the host immune system. Membrane type-1 matrix metalloproteinase (MT1-MMP) is strongly associated with many cancer types and is up-regulated in the aggressive, metastatic neoplasms. During the past few years, there has been an increasing appreciation of the important, albeit incompletely understood, role of MT1-MMP in cancer. We have discovered, using cell-free and cell-based assays in vitro, that MT1-MMP proteolysis specifically targets C3b, an essential component of the complement propagation pathway. MT1-MMP proteolysis liberates the deposited C3 activation fragments from the cell surface. The shedding of these cell-deposited opsonins by MT1-MMP inhibits the complement cascade and protects breast carcinoma MCF7 cells from direct complement-mediated injury in the in vitro tests. The functional link associating MT1-MMP with the host immune system, heretofore unrecognized, may empower tumors with an escape mechanism that contributes to the protection against the host anti-tumor immunity as well as to the survival of invading and metastatic malignant cells in the bloodstream.

Presentation of antigen by endothelial cells and chemoattraction are required for homing of insulin-specific CD8+ T cells.

Activated insulin-specific CD8(+) T cells (IS-CD8(+) cells) home to the pancreas, destroy beta 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 beta 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.

Contribution of Fas to diabetes development.

Fas (Tnfrsf6, Apo-1, CD95) is a death receptor involved in apoptosis induced in many cell types. Fas have been shown to be expressed by insulin-producing beta cells in mice and humans. However, the importance of Fas in the development of autoimmune diabetes remains controversial. To further evaluate the importance of Fas in pathogenesis of diabetes, we generated NOD mice (nonobese diabetic mice developing spontaneous autoimmune diabetes) with beta cell-specific expression of a dominant-negative point mutation in a death domain of Fas, known as lpr(cg) or Fas(cg). Spontaneous diabetes was significantly delayed in NOD mice expressing Fas(cg), and the effect depended on the expression level of the transgene. However, Fas(cg)-bearing mice were still sensitive to diabetes transferred by splenocytes from overtly diabetic NOD mice. At the same time, Fas(cg) expression did neutralize the accelerating effect of transgenic Fas-ligand expressed by the same beta cells. Thus, both Fas-dependent and -independent mechanisms are involved in beta cell destruction, but interference with the Fas pathway early in disease development may retard or prevent diabetes progression.