Involvement of plasmin-mediated extracellular activation of progalanin in angiogenesis

Detection of galanin receptors in the spinal cord in experimental autoimmune encephalomyelitis

AIMS

The neuropeptide galanin is a widely distributed neurotransmitter/neuromodulator that regulates a variety of physiological processes and also participates in the regulation of stress responses. The aims of the present study were to investigate the expression of galanin receptors (GalR1, GalR2, GalR3) in the spinal cords in a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE) using qPCR analysis and to determine GalR1 cellular localization (oligodendrocytes, microglia, astrocytes, ependymal cells, and endothelial cells in the capillaries) by immunohistochemistry.

METHODS

Twelve samples from the EAE group and 14 samples from the control group were analyzed. Spinal cords samples were obtained at the peak of the EAE disease.

RESULTS

The GalR1 mRNA level was significantly decreased in the EAE mice compared with the controls (P=0.016), whereas the mRNA levels of GalR2 and GalR3 were not significantly different for the EAE and the control mice. No significant correlations were found between the severity of the EAE disease and the mRNA levels of GalR1, GalR2 and GalR3. Immunochemical detection of the GalR1 revealed its expression in the ependymal and endothelial cells. Additionally, a weak GalR1 immunoreactivity was occasionally detected in the oligodendrocytes.

CONCLUSION

This study provides additional evidence of galanin involvement in EAE pathophysiology, but this has to be further investigated.

The Plasminogen-Activator Plasmin System in Physiological and Pathophysiological Angiogenesis

Angiogenesis is a process associated with the migration and proliferation of endothelial cells (EC) to form new blood vessels. It is involved in various physiological and pathophysiological conditions and is controlled by a wide range of proangiogenic and antiangiogenic molecules. The plasminogen activator–plasmin system plays a major role in the extracellular matrix remodeling process necessary for angiogenesis. Urokinase/tissue-type plasminogen activators (uPA/tPA) convert plasminogen into the active enzyme plasmin, which in turn activates matrix metalloproteinases and degrades the extracellular matrix releasing growth factors and proangiogenic molecules such as the vascular endothelial growth factor (VEGF-A). The plasminogen activator inhibitor-1 (PAI-1) is the main inhibitor of uPA and tPA, thereby an inhibitor of pericellular proteolysis and intravascular fibrinolysis, respectively. Paradoxically, PAI-1, which is expressed by EC during angiogenesis, is elevated in several cancers and is found to promote angiogenesis by regulating plasmin-mediated proteolysis and by promoting cellular migration through vitronectin. The urokinase-type plasminogen activator receptor (uPAR) also induces EC cellular migration during angiogenesis via interacting with signaling partners. Understanding the molecular functions of the plasminogen activator plasmin system and targeting angiogenesis via blocking serine proteases or their interactions with other molecules is one of the major therapeutic strategies scientists have been attracted to in controlling tumor growth and other pathological conditions characterized by neovascularization.

Matrix metalloproteinases participation in the metastatic process and their diagnostic and therapeutic applications in cancer

Matrix metalloproteinases (MMPs) participate from the initial phases of cancer onset to the settlement of a metastatic niche in a second organ. Their role in cancer progression is related to their involvement in the extracellular matrix (ECM) degradation and in the regulation and processing of adhesion and cytoskeletal proteins, growth factors, chemokines and cytokines. MMPs participation in cancer progression makes them an attractive target for cancer therapy. MMPs have also been used for theranostic purposes in the detection of primary tumor and metastatic tissue in which a particular MMP is overexpressed, to follow up on therapy responses, and in the activation of cancer cytotoxic pro-drugs as part of nano-delivery-systems that increase drug concentration in a specific tumor target. Herein, we review MMPs molecular characteristics, their synthesis regulation and enzymatic activity, their participation in the metastatic process, and how their functions have been used to improve cancer treatment.

Expression of a urokinase-type plasminogen activator during tumor growth leads to angiogenesis via galanin activation in tumor-bearing mice

Small-cell lung carcinoma releases progalanin. The released progalanin is activated via a nonclassical processing pathway, being processed into an active form of galanin (1-20) by plasmin in extracellular components. Plasmin is produced from plasminogen activators. To clarify the regulation of progalanin via plasminogen activation by urokinase and tissue-plasminogen activator (t-PA), we investigated the regulation mechanism for urokinase and t-PA expression and their effect on galanin activation. Additionally, we studied the effect of activated galanin on angiogenesis. To determine the effect of cell density, we measured the expression levels of urokinase and t-PA using real-time PCR and plasminogen/gelatin zymography in a cell culture. The urokinase expression increased under both high cell density and presence of cell membrane fractions. However, urokinase increments induced by conditioned medium were low. These results indicate that expression of plasminogen activators is regulated by cell membrane factors. We used tumor-bearing mice to clarify the expression of plasminogen activators and galanin activation. Real-time PCR showed that urokinase was substantially higher in the central parts of tumors compared to the periphery, and this was confirmed by plasminogen/gelatin zymography. To evaluate the biological effect of plasminogen activators on tumor growth, we used tranexamic acid as a plasminogen inhibitor. Tranexamic acid decreased galanin (1-20) and the hemoglobin content of tumors and suppressed tumor growth. Additionally, galanin had no effect on the hemoglobin content of tumors derived from cells lacking GALR2. These results demonstrate the regulation of urokinase expression in tumors through progalanin activation in extracellular compartments, and confirm that galanin plays a role in angiogenesis.

Identification of Protease Specificity Using Biotin-Labeled Substrates

BACKGROUND

Proteolysis constitutes a major post-translational modification. For example, proteases regulate the activation or inactivation of various proteins, such as enzymes, growth factors, and peptide hormones. Proteases have substrate specificity, and protease expression regulates the specific and regional activation or inactivation of several functional proteins.

METHODS

We demonstrate a novel method for determining protease specificity through the use of MALDI-TOF mass spectrometry with biotin-labeled substrates.

RESULTS

This method was able to determine the specificity of TPCK-trypsin, V8 protease, elastase and cyanogen bromide cleavage, and the results were similar to previous reports. In addition, the method can be used to measure crude samples, such as tumor extracts.

CONCLUSION

We demonstrated that this method could identify protease specificity after simple processing, even for crude samples.

Melanin production through novel processing of proopiomelanocortin in the extracellular compartment of the auricular skin of C57BL/6 mice after UV-irradiation

The production of melanin is regulated by α-melanocyte-stimulating hormone (α-MSH), which is produced from proopiomelanocortin (POMC). Keratinocytes release POMC along with lower levels of α-MSH and ACTH. To clarify the mechanism of melanogenesis after ultraviolet (UV)-irradiation, this study focused on the expression of POMC and POMC-derived peptides after UV-irradiation. Western blot analysis and immunoassays indicated that both POMC and α-MSH-like immunoreactivity (α-MSH-LI) increased after UV-irradiation. However, other POMC-derived products were very low. In hypophysectomized mice, α-MSH-LI increased to the same level as in control mice after UV-irradiation. Structural analysis revealed that the major α-MSH-LI product was ACTH(1–8). Furthermore, ACTH(1–8) competed with [¹²⁵I]-α-MSH for receptor binding and increased melanin production via a melanocortin-1 receptor. These results suggested that melanin was produced through ACTH(1–8) after UV-irradiation. Trypsin-like enzymatic activity, which is responsible for POMC activation, increased after UV-irradiation and was identified as tryptase. In mast cell-deficient mice, which do not produce tryptase, α-MSH-LI levels were unchanged after UV-irradiation. The present study demonstrates the production of ACTH(1–8) from POMC by tryptase, which is a novel peptide-processing mechanism in the extracellular compartment of the skin.

The G protein-coupled receptor GALR2 promotes angiogenesis in head and neck cancer

Squamous cell carcinoma of the head and neck (SCCHN) is an aggressive disease with poor patient survival. Galanin receptor 2 (GALR2) is a G protein-coupled receptor that induces aggressive tumor growth in SCCHN. The objective of this study was to investigate the mechanism by which GALR2 promotes angiogenesis, a critical oncogenic phenotype required for tumor growth. The impact of GALR2 expression on secretion of proangiogenic cytokines in multiple SCCHN cell lines was investigated by ELISA and in vitro angiogenesis assays. Chemical inhibitor and genetic knockdown strategies were used to understand the key regulators. The in vivo impact of GALR2 on angiogenesis was investigated in mouse xenograft, chick chorioallantoic membrane, and the clinically relevant mouse orthotopic floor-of-mouth models. GALR2 induced angiogenesis via p38-MAPK-mediated secretion of proangiogenic cytokines, VEGF, and interleukin-6 (IL-6). Moreover, GALR2 activated small-GTP-protein, RAP1B, thereby inducing p38-mediated inactivation of tristetraprolin (TTP), which functions to destabilize cytokine transcripts. This resulted in enhanced secretion of proangiogenic cytokines and angiogenesis in vitro and in vivo. In SCCHN cells overexpressing GALR2, inactivation of TTP increased secretion of IL-6 and VEGF, whereas inhibition of p38 activated TTP and decreased cytokine secretion. Here, we report that GALR2 stimulates tumor angiogenesis in SCCHN via p38-mediated inhibition of TTP with resultant enhanced cytokine secretion. Given that p38 inhibitors are in clinical use for inflammatory disorders, GALR2/p38-mediated cytokine secretion may be an excellent target for new adjuvant therapy in SCCHN.