Hypoxia-Inducible Factor α Subunits Regulate Tie2-Expressing Macrophages That Influence Tumor Oxygen and Perfusion in Murine Breast Cancer

Tie2-expressing monocytes/macrophages (TEMs) are a distinct subset of proangiogenic monocytes selectively recruited to tumors in breast cancer. Because of the hypoxic nature of solid tumors, we investigated if oxygen, via hypoxia-inducible transcription factors HIF-1α and HIF-2α, regulates TEM function in the hypoxic tumor microenvironment. We orthotopically implanted PyMT breast tumor cells into the mammary fat pads of syngeneic LysMcre, HIF-1α fl/fl /LysMcre, or HIF-2α fl/fl /LysMcre mice and evaluated the tumor TEM population. There was no difference in the percentage of tumor macrophages among the mouse groups. In contrast, HIF-1α fl/fl /LysMcre mice had a significantly smaller percentage of tumor TEMs compared with control and HIF-2α fl/fl /LysMcre mice. Proangiogenic TEMs in macrophage HIF-2α-deficient tumors presented significantly more CD31+ microvessel density but exacerbated hypoxia and tissue necrosis. Reduced numbers of proangiogenic TEMs in macrophage HIF-1α-deficient tumors presented significantly less microvessel density but tumor vessels that were more functional as lectin injection revealed more perfusion, and functional electron paramagnetic resonance analysis revealed more oxygen in those tumors. Macrophage HIF-1α-deficient tumors also responded significantly to chemotherapy. These data introduce a previously undescribed and counterintuitive prohypoxia role for proangiogenic TEMs in breast cancer which is, in part, suppressed by HIF-2α.

Macrophage colony-stimulating factor augments Tie2-expressing monocyte differentiation, angiogenic function, and recruitment in a mouse model of breast cancer

Reports demonstrate the role of M-CSF (CSF1) in tumor progression in mouse models as well as the prognostic value of macrophage numbers in breast cancer patients. Recently, a subset of CD14+ monocytes expressing the Tie2 receptor, once thought to be predominantly expressed on endothelial cells, has been characterized. We hypothesized that increased levels of CSF1 in breast tumors can regulate differentiation of Tie2- monocytes to a Tie2+ phenotype. We treated CD14+ human monocytes with CSF1 and found a significant increase in CD14+/Tie2+ positivity. To understand if CSF1-induced Tie2 expression on these cells improved their migratory ability, we pre-treated CD14+ monocytes with CSF1 and used Boyden chemotaxis chambers to observe enhanced response to angiopoietin-2 (ANG2), the chemotactic ligand for the Tie2 receptor. We found that CSF1 pre-treatment significantly augmented chemotaxis and that Tie2 receptor upregulation was responsible as siRNA targeting Tie2 receptor abrogated this effect. To understand any augmented angiogenic effect produced by treating these cells with CSF1, we cultured human umbilical vein endothelial cells (HUVECs) with conditioned supernatants from CSF1-pre-treated CD14+ monocytes for a tube formation assay. While supernatants from CSF1-pre-treated TEMs increased HUVEC branching, a neutralizing antibody against the CSF1R abrogated this activity, as did siRNA against the Tie2 receptor. To test our hypothesis in vivo, we treated PyMT tumor-bearing mice with CSF1 and observed an expansion in the TEM population relative to total F4/80+ cells, which resulted in increased angiogenesis. Investigation into the mechanism of Tie2 receptor upregulation on CD14+ monocytes by CSF1 revealed a synergistic contribution from the PI3 kinase and HIF pathways as the PI3 kinase inhibitor LY294002, as well as HIF-1α-deficient macrophages differentiated from the bone marrow of HIF-1αfl/fl/LysMcre mice, diminished CSF1-stimulated Tie2 receptor expression.

IL-8 inhibits isoproterenol-stimulated ciliary beat frequency in bovine bronchial epithelial cells

Mucociliary clearance is a critical host defense that protects the lung. The mechanisms by which mucociliary function is altered by inflammation are poorly defined. Chronic exposure to cigarette smoke decreases ciliary beating and interferes with proper airway clearance. Bronchoalveolar lavage (BAL) fluid from smokers and ex-smokers has increased amounts of IL-8, which has played a critical role in airway inflammation. We hypothesized that IL-8 might interfere with stimulated ciliary beating in airway epithelium. To test this hypothesis, we stimulated bovine ciliated bronchial epithelial cells (BBECs) with a known activator of ciliary beat frequency (CBF), isoproterenol (ISO; 100 microM), in the presence or absence of IL-8 (100 pg/mL). We measured CBF digitally using the Sisson-Ammons Video Analysis (SAVA) system. CBF increased in untreated cells exposed to ISO (approximately 3 Hz) over baseline. In contrast, cells pre-incubated with IL-8 failed to respond to ISO. Pretreatment with IL-8 also blocked ISO-stimulated cAMP-dependent kinase (PKA) activation, which is known to control ISO-stimulated CBF. In addition, IL-8 pretreated cells revealed a marked decrease in PKA activity when cells were stimulated with forskolin (FSK; 10 microM). Cells were assayed specifically for cAMP-phosphodiesterase (PDE) activity. ISO-stimulated cells demonstrated an increase in PDE activity as compared to control. Pretreatment with IL-8 had no effect on ISO-stimulated PDE activity. Collectively, these data suggest that IL-8 appears to mediate its effect at the level of adenylyl cyclase. It is also possible that IL-8 may not only act as a chemotactic agent, but also as a potential autocrine/paracrine inhibitor of PKA-mediated stimulation of ciliary motility. In conclusion, IL-8 inhibits beta-agonist dependent ciliostimulation and such inhibition of stimulated ciliary activity may contribute to the impaired mucociliary clearance seen in airway diseases. Furthermore, since IL-8 levels are increased in the airway of cigarette smokers, it is likely they may be more resistant to the cilio and muco-ciliostimulating effects of beta-agonists.

The differential effect of VIP and PACAP on guinea pig gallbladder in vitro

OBJECTIVES

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a recently identified member of the secretin/glucagon/vasoactive intestinal peptide (VIP) family. Like VIP, PACAP is largely inhibitory in the gastrointestinal tract. The aim of our work was to characterize the effects of PACAP on both contraction and relaxation of guinea pig gallbladder (GPGB) muscle.

METHODS

Gallbladder muscle strips were obtained from male Dunkin-Hartley guinea pigs (250-350 g). Isometric tension was measured in strips suspended in gassed (95% O2, 5% CO2) Krebs' solution at 37 degrees C and equilibrated for 60 min. Cumulative additions of VIP or PACAP (10(-9)-10(-6) mol/l) were performed with strips at basal tone or with strips pre-contracted with cholecystokinin-octapeptide (CCK-8).

RESULTS

VIP had no effect on basal tone, in contrast with PACAP which produced concentration-dependent contraction to a maximum of 57.9 +/- 24.3% of control (CCK 3 x 10(-7) mol/l). The highest concentration (10(-6) mol/l) of VIP produced a 32 +/- 6% relaxation of 3 x 10(-9) mol/l CCK-8-contracted GPGB. With 3 x 10(-8) mol/l CCK-contracted GPGB strips, VIP produced a 26.7 +/- 6.6% relaxation. PACAP produced a further concentration-dependent contraction of 3 x 10(-9) mol/l CCK-contracted strips which reached 17.5 +/- 9.9% at the maximal concentration used (10(-6) mol/l). PACAP produced a concentration-dependent relaxation of 3 x 10(-8) mol/l CCK-contracted strips which reached a maximum relaxation of 19 +/- 5% of the control.

CONCLUSIONS

PACAP has a dual effect on guinea pig gallbladder motility in vitro, producing contraction in the basal state, and both contraction and relaxation in the CCK-contracted state. This is in contrast to the effects of VIP, a closely related peptide.

Physiological roles of matrix metalloproteinases: implications for tumor growth and metastasis

Physiological processes involving remodelling of the extracellular matrix, such as wound healing, embryogenesis, angiogenesis, and the female reproductive cycle, require the activity of matrix metalloproteinases (MMPs). This group of proteases degrades basal membranes and connective tissues and plays an essential role in the homeostasis of the extracellular matrix. An imbalance in the expression or activity of MMPs can have important consequences in diseases such as multiple sclerosis, Alzheimer's disease, or the development of cancers. Because of the pathophysiological importance of MMPs, their activity is highly controlled in order to confine them to specific areas. An activation cascade, initiated by the proteolysis of plasminogen, cleaves proMMPs, and every step is controlled by specific activators or inhibitors. MMPs destabilize the organization of the extracellular matrix and influence the development of cancer by contributing to cell migration, tumor cell proliferation, and angiogenesis. Accordingly, these proteases possess an important role in cell-matrix interactions by affecting fundamental processes such as cell differentiation and proliferation. Therefore, the characterization of MMPs involved in specific types and stages of tumors will significantly improve the diagnosis and treatment of these cancers in humans.

Biological and molecular analyses of structurally reduced analogues of endothelin-1

Structurally reduced analogues of endothelin-1 (ET-1) were synthesized through linking with an aliphatic spacer [aminocaproic acid (Aca)], segment 3-11 of ET-1 to carboxyl-terminal fragments of various lengths (16-21, 17-21,...,21). The peptides were prepared in their linear or cyclic form, and a formyl group was or was not introduced on the Trp21 side chain. Pharmacological studies were carried out with the guinea pig lung parenchyma paradigm and the rat thoracic aorta bioassay. In the rat aorta, an ET(A) receptor preparation, all of the analogues were inactive. However, in the lung parenchyma, we observed that among the linear formylated derivatives, [Cys(Acm)3,11,Trp(For)21]-(3-11)-Aca-(17-21)ET was a partial agonist. In this series, the presence of His16, as in [Cys(Acm)3,11,Trp(For)21]-(3-11)-Aca-(16-21)ET, caused a decrease in contractile activity, suggesting that the imidazole group disfavors the proper interaction of the linear molecule with the ETB receptors of the lung parenchyma. The loss of biological activity of the deformylated linear analogues strongly suggested that the formyl group played a stabilizing role in the structure of the linear molecules. Interestingly, molecular modeling studies indicated the adoption of different conformations by the formylated and the nonformylated analogues. In contrast, the stabilizing effect of the formyl group was not observed with the cyclic compounds. Furthermore, the presence of His16 favored the contractile activity of the cyclic peptides. Finally, the results demonstrated that the carboxyl-terminal residues 18-21 are required for the activity in the guinea pig lung parenchyma ETB receptors.

Potential roles for endothelins in systemic inflammatory response syndrome with a particular relationship to cytokines

Endothelins (ETs) are multifunctional isopeptides and their role in several pathophysiologies is slowly emerging. They are possible therapeutic targets in sepsis and other systemic inflammatory response syndromes (SIRS). In such conditions, elevated concentrations of ETs have been reported, together with other proinflammatory markers such as several cytokines. Some of the cytokines even modulate the expression, production, and release of ETs from cells and also the biological responsiveness of ETs into the circulation. Here, we systematically review the literature and discuss the role of these peptides in affecting vascular and inflammatory responses in SIRS. This review also intends to provide a better understanding of the mechanisms of ETs and their interrelationships to other mediators, mainly cytokines, in SIRS. There is no doubt that ETs are useful markers of vascular injury in SIRS. From experimental evidence in animals, endothelins, as potent vasoconstrictors, play a beneficial central compensatory role against the loss of vascular tone associated with SIRS. Conversely, endothelins compromise the circulation in several vascular beds and exacerbate conditions in which inadequate perfusion already exists during the early stages of SIRS. Since no single magic solution has been found for complex diseases related to SIRS, we should look toward a group of mediators, such as cytokines and endothelins, acting as team players.