Induction of SPARC by VEGF in Human Vascular Endothelial Cells

Abstract

SPARC/osteonectin/BM-40 is a matricellular protein that is thought to be involved in angiogenesis and endothelial barrier function. Previously, we have detected high levels of SPARC expression in endothelial cells (ECs) adjacent to carcinomas of kidney and tongue. Although SPARC-derived peptide showed an angiogenic effect, intact SPARC itself inhibited the mitogenic activity of vascular endothelial growth factor (VEGF) for ECs by the inhibiting phosphorylation of flt-1 (VEGF receptor 1) and subsequent ERK activation. Thus, the role of SPARC in tumor angiogenesis, stimulation or inhibition, is still unclear. To clarify the role of SPARC in tumor growth and progression, we determined the effect of VEGF on the expression of SPARC in human microvascular EC line, HMEC-1, and human umbilical vein ECs. VEGF increased the levels of SPARC protein and steady-state levels of SPARC mRNA in serum-starved HMEC-1 cells. Inhibitors (SB202190 and SB203580) of p38, a mitogen-activated protein (MAP) kinase, attenuated VEGF-stimulated SPARC production in ECs. Since intact SPARC inhibits phosphorylation ERK MAP kinase in VEGF signaling, it was suggested that SPARC plays a dual role in the VEGF functions, tumor angiogenesis, and extravasation of tumors mediated by the increased permeability of endothelial barrier function.Key Words: endothelial cells; SPARC/osteonectin/ BM-40; angiogenesis; VEGF; MAP kinase. SPARC/osteonectin/BM-40 is a matricellular protein with a molecular mass of 43 kDa and is known to have a variety of functions. For example, SPARC inhibits the formation of focal adhesion (1) and the production of basement membrane components (2, 3), increases the permeability of endothelial barriers (4), and induces the production and activation of matrix metallo-proteinases (5, 6). In addition, SPARC promotes the motility of tumor cells such as renal cell carcinoma (7) and malignant prostatic cancer cell lines (8). A high level of SPARC expression has been frequently observed in variety of malignant tumors (9-15), and its fragment, the (K)GHK motif, induces angiogenesis in vivo (16). These data suggest that SPARC contributes tumor progression.Angiogenesis is an essential process for tumor growth, and an increase in it raises the risk of tumor metastasis incidence. Since vascular endothelial growth factor (VEGF), which is a potent angiogenic factor, effectively stimulates tube/cord formation by vascular endothelial cells (ECs), a high productive ability for VEGF secretion is thought to be an important malignant phenotype of tumors. Paley et al. (17) determined the localization of VEGF and SPARC in clinical specimens of malignant ovarian carcinomas, and showed that VEGF and SPARC were expressed in the tumor cells and adjacent stromal cells, respectively. We also detected SPARC expression in ECs adjacent to carcinomas of the kidney (18) and tongue (Kato et al. unpublished data) which were producing VEGF. Although SPARC-derived (K)GHK peptide induces angiogenesis in vivo, SPARC was reported to inhibit the mitogenic activ...

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“…19 The exact role of SPARC in tumor angiogenesis is still unclear but may include a role in VEGF (vascular endothelial growth factor) functions and in extravasation of tumors cells mediated by increased permeability of the endothelial barrier. 17 SPARC overexpression has previously been associated with human tumors. 20 Porte et al 21 identified an association of SPARC with colorectal carcinoma, where neoplastic progression was associated with overexpression of the stromelysin-3 and SPARC genes.…”

“…15,16 SPARC increases the production of collagenase, stromelysin, gelatinase, fibronectin and laminin in fibroblasts. 17 This causes degradation of both interstitial and basement membrane matrices 18 and increases endothelial permeability with the appearance of intercellular gaps, which provide a pathway for extravasation of tumor cells. 19 The exact role of SPARC in tumor angiogenesis is still unclear but may include a role in VEGF (vascular endothelial growth factor) functions and in extravasation of tumors cells mediated by increased permeability of the endothelial barrier.…”

Acidic Extracellular pH Induces Matrix Metalloproteinase-9 Expression in Mouse Metastatic Melanoma Cells through the Phospholipase D-Mitogen-activated Protein Kinase Signaling

“…Preparation of Conditioned Medium (CM) for Zymography-Proteins in CM were precipitated with 3 volumes of ethanol for at least 3 h at Ϫ80°C and collected by centrifugation at 15,000 ϫ g for 30 min at 4°C (29). After drying at room temperature, the precipitates were dissolved in PBS or mixed directly with SDS sample buffer (0.5 mM Tris-HCl (pH 6.8), 1% SDS, 0.2% glycerol).…”

Vascular Endothelial Growth Factor Receptor 3 Signaling Contributes to Angioobliterative Pulmonary Hypertension

“…1 J ). Kupprion et al 52 have shown that SPARC inhibits the mitogenic effect of VEGF in microvascular endothelial cells, and there are multiple interactions between SPARC and VEGF signaling; 53,54 SPARC is induced by VEGF in vascular endothelial cells 55 and affects wound healing in a cell type-specific fashion. 56 Treatment of SuHx rats with the VEGFR3 inhibitor MAZ51 ameliorates the severity of pulmonary hypertension and partially prevents lumen obliteration Treatment of SuHx rats with every-other-day dosing of MAZ51 reduced right ventricular systolic pressure (RVSP) without affecting RV hypertrophy (Fig.…”