A PI-3 kinase-dependent, Stat1-independent signaling pathway regulates interferon-stimulated monocyte adhesion

Type I interferon (IFN)-alpha/beta and type II IFN-gamma induce the expression of early response genes through activation of the Janus tyrosine kinase/signal transducer and activator of transcription (Stat) pathway. Although IFNs regulate a variety of other signaling cascades, little is known about how they contribute to the biological activities of these cytokines. In this study, we demonstrate that IFN-beta or IFN-gamma induces the phosphorylation of the serine/threonine kinase Akt in primary human peripheral blood monocytes. Abrogation of the IFN-stimulated Akt activation by phosphatidylinositol-3 kinase (PI-3K) inhibitors prevents IFN-induced adhesion in these cells, and IFN activation of the Stat1-dependent guanylate-binding protein (GBP) gene is not affected. Importantly, Stat1-deficient bone marrow macrophages displayed a similar level of IFN-gamma-stimulated adhesion compared with macrophages derived from wild-type littermates. These findings demonstrate for the first time that IFN stimulation of a PI-3K signaling cascade modulates the ability of these cytokines to regulate monocyte adhesion, and this process does not require the expression of Stat1, a primary mediator of IFN-gamma signaling.

A novel function for tissue inhibitor of metalloproteinases-3 (TIMP3): inhibition of angiogenesis by blockage of VEGF binding to VEGF receptor-2

Tissue inhibitor of metalloproteinases-3 (TIMP3) is one of four members of a family of proteins that were originally classified according to their ability to inhibit matrix metalloproteinases (MMP). TIMP3, which encodes a potent angiogenesis inhibitor, is mutated in Sorsby fundus dystrophy, a macular degenerative disease with submacular choroidal neovascularization. In this study we demonstrate the ability of TIMP3 to inhibit vascular endothelial factor (VEGF)-mediated angiogenesis and identify the potential mechanism by which this occurs: TIMP3 blocks the binding of VEGF to VEGF receptor-2 and inhibits downstream signaling and angiogenesis. This property seems to be independent of its MMP-inhibitory activity, indicating a new function for this molecule.

Expression of Sorsby's fundus dystrophy mutations in human retinal pigment epithelial cells reduces matrix metalloproteinase inhibition and may promote angiogenesis

Sorsby's fundus dystrophy (SFD) is an autosomal dominant degenerative disease of the macula caused by mutations in the tissue inhibitor of metalloproteinase-3 (TIMP-3) gene. Choroidal neovascularization is a hallmark of this disease, which closely resembles the exudative form of age-related macular degeneration. However, the mechanism by which TIMP-3 mutations induce the disease phenotype in SFD remains unknown. To address this question we established human retinal pigment epithelial cell lines expressing wild type or S156C (Ser(156) changed to cysteine) mutant TIMP-3. S156C TIMP-3 had reduced matrix metalloproteinase (MMP) inhibitory activity in retinal pigment epithelial cells and resulted in increased secretion and activation of gelatinase A and B. The conditioned medium from these cells induced angiogenesis in "in vivo" chick chorioallantoic membrane assays that could be reversed with recombinant wild type TIMP-3. Our data indicate that the choroidal neovascularization in SFD may be a result of increased MMP activity, which could lead to the stimulation of angiogenesis. These results also suggest the potential therapeutic use of TIMP-3 or synthetic MMP inhibitors in this disease.

A direct interaction between oncogenic Ha-Ras and phosphatidylinositol 3-kinase is not required for Ha-Ras-dependent transformation of epithelial cells

Cells expressing oncogenic Ras proteins transmit a complex set of signals that ultimately result in constitutive activation of signaling molecules, culminating in unregulated cellular function. Although the role of oncogenic Ras in a variety of cellular responses including transformation, cell survival, differentiation, and migration is well documented, the direct Ras/effector interactions that contribute to the different Ras biological end points have not been as clearly defined. Observations by other groups in which Ras-dependent transformation can be blocked by expression of either dominant negative forms of Phosphatidylinositol (PI) 3-kinase or PTEN, a 3-phosphoinositide-specific phosphatase, support an essential role for PI 3-kinase and its lipid products in the transformation process. These observations coupled with the in vitro observations that the catalytic subunits of PI 3-kinase, the p110 isoforms, bind directly to Ras-GTP foster the implication that a direct interaction between an oncogenic Ras protein and PI 3-kinase are causal in the oncogenicity of mutant Ras proteins. Using an activated Ha-Ras protein (Y64G/Y71G/F156L) that fails to interact with PI 3-kinase, we demonstrate that oncogenic Ha-Ras does not require a direct interaction with PI 3-kinase to support anchorage-independent growth of IEC-6 epithelial cells. We do find, however, that IEC-6 cells expressing an oncogenic Ha-Ras protein that no longer binds PI 3-kinase are greatly impaired in their ability to migrate toward fibronectin.

Motility and invasion are differentially modulated by Rho family GTPases

Cell migration in vivo often requires invasion through tissue matrices. Currently little is known regarding the signaling pathways that regulate cell invasion through three-dimensional matrices. The small GTPases Cdc42, Rac and Rho are key regulators of actin cytoskeletal and adhesive structures. We now show that expression of dominant negative forms of either Cdc42, Rac or Rho inhibited PDGF-BB-stimulated Rat1 fibroblast invasion into 3D collagen matrices, indicating that the activity of each of these GTPases is necessary for cell invasion. In contrast, only Rac activation was required for PDGF-BB-stimulated locomotion across a planar substrate in the Boyden chamber. Interestingly, PDGF-induced invasion was also strongly inhibited by expression of constitutively active forms of Cdc42 or Rho, and to a lesser extent by constitutively active Rac. We also show that constitutively active V12-Rac significantly stimulated basal Rat1 fibroblast invasion, independent of PI-3-kinase activity, and that this effect was suppressed by the effector mutant V12/H40-Rac. These results suggest that cellular invasion may require an optimal level of activation of Cdc42, Rho and Rac, and that migration and invasion are differentially modulated by Rho family GTPases.

Corticotropin-releasing hormone stimulates angiogenesis and epithelial tumor growth in the skin

The hypothalamic neuropeptide corticotropin-releasing hormone is the major hypothalamic regulator of the endocrine pituitary-adrenal axis. Corticotropin-releasing hormone is also expressed in many peripheral sites, where its functions are unclear. It is also secreted by diverse neoplasms, where it may be associated with malignant behavior. To provide information regarding the function of corticotropin-releasing hormone in peripheral sites and in tumors, we asked whether corticotropin-releasing hormone has angiogenic properties. In vitro, we found that human corticotropin-releasing hormone specifically stimulates endothelial chemotaxis via a corticotropin-releasing hormone receptor-dependent mechanism. In vivo, subcutaneous inoculation of nude mice with human epithelial tumor cells engineered to secrete corticotropin-releasing hormone was associated with significantly enhanced angiogenesis (2.3-fold over control) and tumor growth (5-fold over control). Peripheral corticotropin-releasing hormone may thus enhance local angiogenesis, which may provide clues to its function outside of the nervous system.

Vascular endothelial growth factor-induced migration of vascular smooth muscle cells in vitro

Angiogenesis is a complex process that includes recruitment and proliferation of mural cells-smooth muscle cells (SMC) and pericytes. Vascular endothelial growth factor (VEGF) has been shown to play an important role in angiogenesis and is an endothelial cell chemoattractant. In addition, certain VEGF isoforms have been implicated in the normal formation of smooth muscle cell-surrounded arteries. Because VEGF's role as a mural cell chemoattractant had not been explored, we examined the ability of VEGF to influence vascular SMC migration in vitro. A Boyden chamber migration assay demonstrated that VEGF (0-100 ng/ml) caused a dose-dependent migration of SMC. VEGF did not cause proliferation of SMC. Reverse transcriptase-polymerase chain reaction analysis demonstrated the presence of both KDR and flt mRNA, two known VEGF receptors, in SMC cultures. Western blot analysis of SMC lysates confirmed these data, revealing bands migrating at approximately 200 kDa and slightly below 200 kDa consistent with KDR and flt. These observations demonstrate that VEGF receptors are present on SMC, and that VEGF can act as an SMC chemoattractant.

Endostatin inhibits VEGF-induced endothelial cell migration and tumor growth independently of zinc binding

Endostatin, produced as recombinant protein in human 293-EBNA cells, inhibits the migration of human umbilical vein endothelial cells (HUVECs) in response to vascular endothelial growth factor (VEGF) in a dose-dependent manner and prevents the subcutaneous growth of human renal cell carcinomas in nude mice at concentrations and in doses that are from 1000- to 100 000-fold lower than those previously reported. The inhibition of migration is not affected by mutations which eliminate Zn or heparin binding and inhibition of tumor growth does not depend on Zn binding. The results of the migration assays suggest that endostatin causes a block at one or more steps in VEGF-induced migration, while VEGF in turn can cause a block of the inhibition by endostatin of VEGF-induced migration of HUVECs.

Angiostatin induces endothelial cell apoptosis and activation of focal adhesion kinase independently of the integrin-binding motif RGD

Angiostatin, a fragment of plasminogen, has been identified and characterized as an endogenous inhibitor of neovascularization. We show that angiostatin treatment of endothelial cells in the absence of growth factors results in an increased apoptotic index whereas the proliferation index is unchanged. Angiostatin also inhibits migration and tube formation of endothelial cells. Angiostatin treatment has no effect on growth factor-induced signal transduction but leads to an RGD-independent induction of the kinase activity of focal adhesion kinase, suggesting that the biological effects of angiostatin relate to subversion of adhesion plaque formation in endothelial cells.

Platelet-derived growth factor and fibronectin-stimulated migration are differentially regulated by the Rac and extracellular signal-regulated kinase pathways

Directed cell migration is essential for a variety of important biological processes ranging from development and angiogenesis to metastasis. Ras plays a pivotal role in the signaling cascade that governs chemotaxis of fibroblasts toward platelet-derived growth factor-BB (PDGF-BB). Ras activates multiple downstream pathways, which include the extracellular signal-regulated kinase (ERK), Rac, and Ral signaling cascades. We therefore investigated the role of the Rac and ERK pathways in cell migration. We showed that migration of fibroblasts toward PDGF-BB is inhibited by expression of dominant negative Asn-17 Rac1. Blocking of the ERK pathway by either expression of dominant negative Ala-218/Ala-222-mitogen-activated protein kinase kinase (A218/A222-MEK1) or by a MEK-specific inhibitor did not inhibit migration toward PDGF-BB. In contrast, migration toward soluble fibronectin was suppressed by inhibition of the ERK pathway but not by Asn-17 Rac1 expression. These results indicate that directed cell migration mediated by different receptor classes in response to different ligands differentially utilizes the Rac and ERK pathways and suggest that Rac might play a critical role in pathological processes such as angiogenesis and metastasis.

Inhibition of angiogenesis by tissue inhibitor of metalloproteinase-3

PURPOSE

It has been established that Sorsby's fundus dystrophy, a dominantly inherited form of blindness, is caused by mutations in the tissue inhibitor of metalloproteinase-3 (TIMP-3) gene. Because choroidal neovascularization is a prominent feature of Sorsby's fundus dystrophy, the authors have examined whether TIMP-3 protein plays a role in the regulation of angiogenesis.

METHODS

Chemotaxis of endothelial cells toward vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) was examined using a modified Boyden chamber assay. Endothelial cells placed in the upper chamber were allowed to migrate through a polycarbonate membrane with 8 microns pores toward VEGF or bFGF present in the lower chamber. Next, the ability of TIMP-3 to inhibit chemotaxis was studied by incubating the cells with varying amounts of TIMP-3 during the assay. Finally, an in vitro angiogenesis assay was performed on collagen gels. Endothelial cells were seeded onto three-dimensional collagen gels. Treatment with bFGF and VEGF induced invasion of the gel and the formation of tube-like structures. TIMPs (1, 2, and 3) were added to the cultures to determine their effect on invasion. An in vivo chorioallantoic membrane (CAM) assay was performed using methylcellulose discs containing bFGF with or without TIMP-3. Induction of new blood vessels was observed with a stereomicroscope.

RESULTS

TIMP-3 inhibits chemotaxis of vascular endothelial cells toward VEGF and bFGF, inhibits collagen gel invasion and capillary morphogenesis in vitro, and inhibits bFGF-induced angiogenesis in the CAM assay in vivo.

CONCLUSIONS

TIMP-3 has the potential to inhibit angiogenesis. These results allow us to speculate on a possible mechanism by which mutant TIMP-3 protein might contribute to the Sorsby fundus dystrophy phenotype.

Signaling mechanisms in growth factor-stimulated cell motility

Most mammalian cells have the capacity to migrate. When placed into culture, cells will generally display a set rate of basal, unstimulated locomotion. The cells will begin to move in one direction and, after some time, change directions resulting in a random walk. External stimuli can influence cell motility in several ways to either enhance or retard the rate of migration (chemokinesis), to change the average amount of cell migration observed before the cell turns (persistence), or to increase the directionality of movement by limiting the number of turns made by the cells. Several factors have been identified that stimulate cell movement, but the signaling mechanisms that mediate this induced cell movement have only recently begun to be studied. In this review, we discuss the signals that support the directional movement of fibroblasts and epithelial cells in response to chemoattractant gradients. The work will emphasize studies carried out by our laboratory and others on the stimulation of cell motility by the PDGF. These results indicate that at least two sets of signaling molecules cooperate to regulate cell motility in vivo. These include phospholipase C-gamma, phosphoinositide-3' kinase and the Ras-GTPase activating protein Ras-GAP. The first set are those which bind to the intracellular domain of the receptor tyrosine kinase and bring about the phosphorylation and/or activation of intracellular effectors proximal to the receptor. The second is a set of down-stream effectors that regulate either the rate of cell movement or the directionality of that movement depending on the cell type. These include Ras and the Ras-related GTPase Rac along with free phosphoinositides and calcium ions that regulate the actin polymerization machinery. Signals that mediate nuclear changes leading to cell proliferation, such as elements of the MAP kinase pathway, do not appear to play a role in PDGF-stimulated cell migration. Current work thus suggests that a coordinated spatial regulation of signaling elements that interact with the cell membrane and cytoskeleton but not necessarily with nuclear elements is the controlling mediator of directional cell motility.

Thymosin beta 15: a novel regulator of tumor cell motility upregulated in metastatic prostate cancer

The Dunning rat prostatic carcinoma is a model system where cell motility closely correlates with the metastatic phenotype. We have identified a novel gene, upregulated in the highly motile and metastatic Dunning cancer cell lines, that represents a new member of the thymosin-beta family, thymosin beta 15. Transfection of antisense thymosin beta 15 constructs into rat prostatic carcinoma cells demonstrates that this molecule positively regulates cell motility, a critical component of the metastatic pathway. Thymosin beta 15 levels are elevated in human prostate cancer and correlate positively with the Gleason tumor grade. Thymosin beta 15 may represent a potential new biochemical marker for human prostate cancer progression.

New activity of spironolactone. Inhibition of angiogenesis in vitro and in vivo

BACKGROUND

The formation of new blood vessels (angiogenesis) is a critical component in a variety of pathological settings, including solid tumor growth, macular degeneration, and atherosclerosis.

METHODS AND RESULTS

We have found that orally administered spironolactone inhibited the area of angiogenesis induced by basic fibroblast growth factor (bFGF) in a rabbit corneal micropocket assay. Additionally, spironolactone inhibited bFGF- and vascular endothelial growth factor-stimulated capillary endothelial cell proliferation in vitro, inhibited bFGF-stimulated capillary endothelial cell chemotaxis in vitro, and caused avascular zones when placed on the chick chorioallantoic membrane. Experiments analyzing spironolactone metabolites revealed that the major human metabolites 6 beta-hydroxy-7 alpha-thiomethyl spironolactone and canrenoic acid retained antiangiogenic activity. The antiangiogenic activity appears to be unrelated to the antiandrogenic and antimineralocorticoid effects of spironolactone.

CONCLUSIONS

These experiments hold promise for the potential use of spironolactone as an orally administered drug for the treatment of many diverse diseases dependent on angiogenesis.

Heterodimers of placenta growth factor/vascular endothelial growth factor. Endothelial activity, tumor cell expression, and high affinity binding to Flk-1/KDR

Here we show that the Escherichia coli expressed monomers of placenta growth factor (PLGF)129 and vascular endothelial growth factor (VEGF)165 can be re-folded in vitro to form PLGF/VEGF heterodimers. The purified recombinant PLGF/VEGF heterodimers and VEGF homodimers have potent mitogenic and chemotactic effects on endothelial cells. However, PLGF/VEGF heterodimers display 20-50-fold less mitogenic activity than VEGF165 homodimers. In contrast, PLGF129 homodimers have little or no effect in these in vitro assays. We also demonstrate the presence of natural PLGF/VEGF heterodimers in the conditioned media of various human tumor cell lines. While PLGF/VEGF heterodimers bind with high affinity to a soluble Flk-1/KDR receptor, PLGF129 homodimers fail to bind to this receptor. Cross-linking of 125I-ligands to human umbilical vein endothelial cells reveals that PLGF/VEGF heterodimers and VEGF165 homodimers, but not PLGF129 homodimers, form complexes with membrane receptors. VEGF165 homodimers and PLGF/VEGF heterodimers stimulate tyrosine phosphorylation of a 220-kDa protein, the expected size for the KDR receptor in human umbilical vein endothelial cells, whereas PLGF129 homodimers are unable to induce tyrosine phosphorylation of this protein. These data indicate that PLGF may modulate VEGF-induced angiogenesis by the formation of PLGF/VEGF heterodimers in cells producing both factors.

A review of tissue inhibitor of metalloproteinases-3 (TIMP-3) and experimental analysis of its effect on primary tumor growth

The family of tissue inhibitors of metalloproteinases (TIMPs) presently numbers four distinct gene products that are specific inhibitors of the matrix metalloproteinases (MMPs). The local balance between MMPs and TIMPs is believed to play a major role in extracellular matrix (ECM) remodeling during development and in diseases such as cancer and arthritis. Unlike the other TIMPs, which are soluble. TIMP-3 is unique in being a component of ECM. Mutations in the human TIMP-3 gene cause a dominantly inherited, adult-onset blindness (Sorsby's fundus dystrophy or SFD). In this article, we summarize what is currently known about TIMP-3, discuss possible mechanisms leading up to SFD, and investigate the effect of TIMP-3 on tumor growth. Breast carcinoma and malignant melanoma cell lines were transfected with TIMP-3 expression plasmids and injected subcutaneously into nude mice. Growth curves of the resulting tumors over a period of 6 to 8 weeks demonstrated that increased expression of TIMP-3 resulted in a statistically significant suppression of tumor growth. Deposition of TIMP-3 in the surrounding ECM by tumor cells may inhibit tumor growth by preventing local expansion of tumor, retarding the release of growth factors sequestered in ECM, or inhibiting angiogenesis. TIMP-3 over-expression had no effect on the growth of the two tumor cell lines in vitro. Because recombinant TIMP-3 inhibits endothelial cell migration and tube formation in response to angiogenic factors, we believe that the effect of TIMP-3 on tumor growth seen in this study may be a consequence of its angiostatic action.

Differential endothelial migration and proliferation to basic fibroblast growth factor and vascular endothelial growth factor

Neovascularization is a feature of a variety of pathological processes. We compared the characteristics of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) on migration and proliferation of human umbilical vein endothelium (HUVEC). Both VEGF and bFGF induced endothelial cell migration at similar concentrations (1/2 max. VEGF = approximately 1.0 ng/ml, bFGF = approximately 5.0 ng/ml). However, VEGF-stimulated migration was two-fold greater than bFGF at 1 and 10 ng/ml (p < 0.05). In contrast, bFGF induced proliferation four-fold more effectively than VEGF (1/2 max. 1 ng/ml and 1.4 ng/ml respectively). Checkerboard migration assays for bFGF showed a predominantly chemokinetic pattern, whereas VEGF was predominantly chemotactic. VEGF and bFGF were not synergistic in monolayer proliferation and migration assays. Three angiogenesis inhibitors, alpha-interferon, TNP-470, and platelet factor-4, inhibited VEGF and bFGF induced cell migration. These results indicate that VEGF and bFGF are chemoattractants that stimulate endothelial migration by different mechanisms and that both can be inhibited by known angiogenesis inhibitors.

The chemotactic response to PDGF-BB: evidence of a role for Ras

The PDGF receptor-beta mediates both mitogenic and chemotactic responses to PDGF-BB. Although the role of Ras in tyrosine kinase-mediated mitogenesis has been characterized extensively, its role in PDGF-stimulated chemotaxis has not been defined. Using cells expressing a dominant-negative ras, we find that Ras inhibition suppresses migration toward PDGF-BB. Overexpression of either Ras-GTPase activating protein (Ras-GAP) or a Ras guanine releasing factor (GRF) also inhibited PDGF-stimulated chemotaxis. In addition, cells producing excess constitutively active Ras failed to migrate toward PDGF-BB, consistent with the observation that either excess ligand or excess signaling intermediate can suppress the chemotactic response. These results suggest that Ras can function in normal cells to support chemotaxis toward PDGF-BB and that either too little or too much Ras activity can abrogate the chemotactic response. In contrast to Ras overexpression, cells producing excess constitutively active Raf, a downstream effector of Ras, did migrate toward PDGF-BB. Cells expressing dominant-negative Ras were able to migrate toward soluble fibronectin demonstrating that these cells retained the ability to migrate. These results suggest that Ras is an intermediate in PDGF-stimulated chemotaxis but may not be required for fibronectin-stimulated cell motility.