Reversible transdifferentiation of blood vascular endothelial cells to a lymphatic-like phenotype in vitro.

Blood vascular cells and lymphatic endothelial cells (BECs and LECs, respectively) form two separate vascular systems and are functionally distinct cell types or lineages with characteristic gene expression profiles. Interconversion between these cell types has not been reported. Here, we show that in conventional in vitro angiogenesis assays, human BECs of fetal or adult origin show altered gene expression that is indicative of transition to a lymphatic-like phenotype. This change occurs in BECs undergoing tubulogenesis in fibrin, collagen or Matrigel assays, but is independent of tube formation per se, because it is not inhibited by a metalloproteinase inhibitor that blocks tubulogenesis. It is also reversible, since cells removed from 3D tubules revert to a BEC expression profile upon monolayer culture. Induction of the lymphatic-like phenotype is partially inhibited by co-culture of HUVECs with perivascular cells. These data reveal an unexpected plasticity in endothelial phenotype, which is regulated by contact with the ECM environment and/or cues from supporting cells.

The activity of a designer tissue inhibitor of metalloproteinases (TIMP)-1 against native membrane type 1 matrix metalloproteinase (MT1-MMP) in a cell-based environment.

The surface-anchored membrane type 1 matrix metalloproteinase (MT1-MMP) degrades a wide range of extracellular matrix components that includes collagens, laminins, fibronectin and the structural proteoglycan aggrecan. The enzyme modulates cell motility and plays an important role in tumour invasion and proliferation. We have previously designed a variant of tissue inhibitor of metalloproteinase (TIMP)-1 bearing a triple mutation (V4A+P6V+T98L, or N-TIMP-1(mt1)) that forms tight binary complex with the soluble catalytic domain of MT1-MMP [M.H. Lee, M. Rapti, G. Murphy, J. Biol. Chem. 278 (2003) 40224-40230]. Here, we report our latest findings on the cellular potency of this mutant against native MT1-MMP in cell-based environment. We show that N-TIMP-1(mt1) is a highly potent inhibitor against the ectodomain form of MT1-MMP (K(i) 9.53nM) with potential for further development as a therapeutic agent. The mutant is devoid of pro-MMP-2-activating capability but is highly effective in blocking MT1-MMP-mediated FITC-labelled collagen and gelatin film degradation in HTC75 fibrosarcoma and MCF7 breast cancer models. Most encouragingly, N-TIMP-1(mt1) is also effective against CD44 shedding in HTC75 cells and able to prevent tubule formation in human umbilical vascular endothelial cells (HUVEC) in a 3D fibrin gel model. We are interested in the development of the TIMPs as therapeutic agents against MT1-MMP related disorders such as cancers. Our findings here indicate the potential for the design of selective TIMPs with refined specificity and possibility for future therapeutic application.

The ADAM metalloproteinases.

The ADAMs (a disintegrin and metalloproteinase) are a fascinating family of transmembrane and secreted proteins with important roles in regulating cell phenotype via their effects on cell adhesion, migration, proteolysis and signalling. Though all ADAMs contain metalloproteinase domains, in humans only 13 of the 21 genes in the family encode functional proteases, indicating that at least for the other eight members, protein-protein interactions are critical aspects of their biological functions. The functional ADAM metalloproteinases are involved in "ectodomain shedding" of diverse growth factors, cytokines, receptors and adhesion molecules. The archetypal activity is shown by ADAM-17 (tumour necrosis factor-alpha convertase, TACE), which is the principal protease involved in the activation of pro-TNF-alpha, but whose sheddase functions cover a broad range of cell surface molecules. In particular, ADAM-17 is required for generation of the active forms of Epidermal Growth Factor Receptor (EGFR) ligands, and its function is essential for the development of epithelial tissues. Several other ADAMs have important sheddase functions in particular tissue contexts. Another major family member, ADAM-10, is a principal player in signalling via the Notch and Eph/ephrin pathways. For a growing number of substrates, foremost among them being Notch, cleavage by ADAM sheddases is essential for their subsequent "regulated intramembrane proteolysis" (RIP), which generates cleaved intracellular domains that translocate to the nucleus and regulate gene transcription. Several ADAMs play roles in spermatogenesis and sperm function, potentially by effecting maturation of sperm and their adhesion and migration in the uterus. Other non-catalytic ADAMs function in the CNS via effects on guidance mechanisms. The ADAM family are thus fundamental to many control processes in development and homeostasis, and unsurprisingly they are also linked to pathological states when their functions are dysregulated, including cancer, cardiovascular disease, asthma, Alzheimer's disease. This review will provide an overview of current knowledge of the human ADAMs, discussing their structure, function, regulation and disease involvement.

Distinct functions of natural ADAM-15 cytoplasmic domain variants in human mammary carcinoma.

Adamalysins [a disintegrin and metalloproteinase (ADAM)] are a family of cell surface transmembrane proteins that have broad biological functions encompassing proteolysis, adhesion, and cell signal regulation. We previously showed that the cytoplasmic domain of ADAM-15 interacts with Src family protein tyrosine kinases and the adaptor protein growth factor receptor binding protein 2 (Grb2). In the present study, we have cloned and characterized four alternatively spliced forms of ADAM-15, which differ only in their cytoplasmic domains. We show that the four ADAM-15 variants were differentially expressed in human mammary carcinoma tissues compared with normal breast. The expression of the individual isoforms did not correlate with age, menopausal status, tumor size or grade, nodal status, Nottingham Prognostic Index, or steroid hormone receptor status. However, higher levels of two isoforms (ADAM-15A and ADAM-5B) were associated with poorer relapse-free survival in node-negative patients, whereas elevated ADAM-15C correlated with better relapse-free survival in node-positive, but not in node-negative, patients. The expression of ADAM-15A and ADAM-15B variants in MDA-MB-435 cells had differential effects on cell morphology, with adhesion, migration, and invasion enhanced by expression of ADAM-15A, whereas ADAM-15B led to reduced adhesion. Using glutathione S-transferase pull-down assays, we showed that the cytoplasmic domains of ADAM-15A, ADAM-15B, and ADAM-15C show equivalent abilities to interact with extracellular signal-regulated kinase and the adaptor molecules Grb2 and Tks5/Fish, but associate in an isoform-specific fashion with Nck and the Src and Brk tyrosine kinases. These data indicate that selective expression of ADAM-15 variants in breast cancers could play an important role in determining tumor aggressiveness by interplay with intracellular signaling pathways.

Intracellular photodynamic therapy with photosensitizer-nanoparticle conjugates: cancer therapy using a 'Trojan horse'.

Phthalocyanine-nanoparticle conjugates have been designed and synthesised for the delivery of hydrophobic photosensitizers for photodynamic therapy (PDT) of cancer. The phthalocyanine photosensitizer stabilized gold nanoparticles have an average diameter of 2-4 nm. The synthetic strategy interdigitates a phase transfer reagent between phthalocyanine molecules on the particle surface that solubilises the hydrophobic photosensitizer in polar solvents enabling delivery of the nanoparticle conjugates to cells. The phthalocyanine is present in the monomeric form on the nanoparticle surface, absorbs radiation maximally at 695 nm and catalytically produces the cytotoxic species singlet oxygen with high efficiency. These properties suggest that the phthalocyanine-nanoparticle conjugates are ideally suited for PDT. In a process that can be considered as cancer therapy using a 'Trojan horse', when the nanoparticle conjugates are incubated with HeLa cells (a cervical cancer cell line), they are taken up thus delivering the phthalocyanine photosensitizer directly into the cell interior. Irradiation of the nanoparticle conjugates within the HeLa cells induced substantial cell mortality through the photodynamic production of singlet oxygen. The PDT efficiency of the nanoparticle conjugates, determined using colorimetric assay, was twice that obtained using the free phthalocyanine derivative. Following PDT with the nanoparticle conjugates, morphological changes to the HeLa cellular structure were indicative of cell mortality via apoptosis. Further evidence of apoptosis was provided through the bioluminescent assay detection of caspase 3/7. Our results suggest that gold nanoparticle conjugates are an excellent vehicle for the delivery of surface bound hydrophobic photosensitizers for efficacious photodynamic therapy of cultured tumour cells.

Metalloproteinases and their inhibitors in tumor angiogenesis.

Angiogenesis is the process by which new blood vessels are formed from preexisting vasculature. It is an essential feature of the female reproductive cycle, embryonic development and wound repair. Angiogenesis has also been identified as a causal or contributing factor in several pathologies, including cancer, where it is a rate-limiting step during tumor progression. Matrix metalloproteinases (MMPs) are a family of soluble and membrane-anchored proteolytic enzymes that can degrade components of the extracellular matrix (ECM) as well as a growing number of modulators of cell function. Several of the MMPs, in particular the gelatinases and membrane-type 1 MMP (MT1-MMP), have been linked to angiogenesis. Potential roles for these proteases during the angiogenic process include degradation of the basement membrane and perivascular ECM components, unmasking of cryptic biologically relevant sites in ECM components, modulation of angiogenic factors and production of endogenous angiogenic inhibitors. This review brings together what is currently known about the functions of the MMPs and the closely related ADAM (a disintegrin and metalloproteinase domain) and ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) families in angiogenesis and considers how this information might be useful in manipulation of the angiogenic process, with a view to constraining tumor progression.

Metalloproteinases and their inhibitors in angiogenesis.

Angiogenesis, the formation of new blood vessels from the pre-existing vasculature, is an integral part of physiological processes such as embryonic development, the female reproductive cycle and wound healing. Angiogenesis is also central to a variety of pathologies including cancer, where it is recognised as being crucial for the growth of solid tumours. Matrix metalloproteinases (MMPs) are a family of soluble and membrane-anchored proteolytic enzymes that can degrade components of the extracellular matrix (ECM) as well as a growing number of modulators of cell function. Several of the MMPs, most notably MMP-2 and -9 and membrane-type-1 MMP (MT1-MMP), have been linked to angiogenesis. Potential roles for these proteases during the angiogenic process include degradation of the basement membrane and perivascular ECM components, liberation of angiogenic factors, production of endogenous angiogenic inhibitors, and the unmasking of cryptic biologically relevant sites in ECM components. This review brings together what is currently known about the functions of the MMPs and the closely related adamalysin metalloproteinase (ADAM) family in angiogenesis, and discusses how this information might be useful in manipulation of the angiogenic process, with a view to controlling aberrant neovascularisation.

Endothelial tubulogenesis within fibrin gels specifically requires the activity of membrane-type-matrix metalloproteinases (MT-MMPs).

Macro- and microvascular endothelial cells (EC) formed tubular structures when cultured within a 3D fibrin matrix, a process that was enhanced by vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF-2), hepatocyte growth factor/scatter factor (HGF/SF) and an angiogenic cocktail composed of nine angiogenic factors. Endothelial tubulogenesis was also increased in co-culture with tumour cells such as U87 glioma cells, but not with non-tumorigenic cell types such as Madin-Darby canine kidney (MDCK) epithelial cells. VEGF/FGF-2-stimulated tube formation was dependent on metalloproteinase function [it is inhibited by the addition of tissue inhibitor of metalloproteinases-2 (TIMP-2)], whereas aprotinin, E64 [trans-epoxysuccinyl-L-leucylamido (4-guanidino)-butane] and pepstatin had no effect. In addition, TIMP-4 also inhibited tubulogenesis, but TIMP-1 or the C-terminal haemopexin domain of matrix metalloproteinase-2 (MMP-2) (PEX) and an anti-MMP-2 function-blocking antibody were unable to block tube formation. This suggests that MMP-2 and other soluble MMPs are not essential for tubulogenesis in fibrin gels, instead TIMP-1-insensitive MMPs, such as members of the membrane type-MMPs (MT-MMP) sub-group (MT1-, MT2-, MT3- or MT5-MMP), are required for this process. Further support for a role for MT1-MMP in endothelial tubulogenesis is that recombinant Y36G N-terminal TIMP-2 mutant protein, which retains an essentially unaltered apparent inhibition constant (K(i)(app)) for several MMPs compared to wild-type N-TIMP-2 but is a 40-fold poorer inhibitor of MT1-MMP, was unable to block tubulogenesis. Furthermore, when EC were cultured within fibrin gels, the mRNA levels of several MMPs (including MT1-MMP, MT2-MMP, MT3-MMP and MMP-2) increased during tubulogenesis. Therefore MT-MMPs and specifically MT1-MMP are likely candidates for involvement during endothelial tubulogenesis within a fibrin matrix, and thus their blockade may be a viable strategy for inhibition of angiogenesis.